ADS1261BIRHBR

Order Now Product Folder Support & Community Tools & Software Technical Documents ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 ADS126x Precision, 5-channel and 10-channel, 40-kSPS, 24-bit, delta-sigma ADCs with PGA and monitors 1 Features 3 Description • The ADS1260 and ADS1261 (ADS126x) are precision, 40-kSPS, delta-sigma (ΔΣ) analog-to-digital converters (ADCs) that include a programmable gain amplifier (PGA). The devices also include a precision voltage reference and internal fault monitors. The sensor-ready ADCs give a high-accuracy, single-chip solution for the most demanding measurements, for example, weigh scales and resistance temperature detectors (RTDs). 1 • • • • • • • • • • • • • • • 24-bit, high-precision ADCs – Offset drift: 1 nV/°C – Gain drift: 0.5 ppm/°C – Noise: 30 nVRMS (20 SPS, gain = 128) – Linearity: 2 ppm CMOS PGA gain: 1 to 128 Wide input voltage range: ±7 mV to ±5 V Data rate: 2.5 SPS to 40 kSPS 2.5-V reference: 2 ppm/°C Simultaneous 50-Hz and 60-Hz rejection mode Single-cycle settling mode Signal and reference monitors 5-V or ±2.5-V power supply Internal temperature sensor Cyclic redundancy check (CRC) Excitation current sources Sensor burn-out current sources Four general-purpose inputs/outputs (ADS1261) AC excitation for bridge sensors (ADS1261) 5-mm × 5-mm VQFN package The ADCs contain an input signal multiplexer, a lownoise PGA (with gains from 1 to 128), a 24-bit ΔΣ modulator, a precision voltage reference, and a programmable digital filter. The high-impedance PGA inputs (1 GΩ) decrease measurement error due to sensor loading. The ADS1260 supports three differential or five singleended inputs. The ADS1261 supports five differential or ten single-ended inputs. The integrated current sources simplify the measurement of RTDs. The flexible digital filter is programmable for singlecycle settled conversions, while supplying simultaneous 50-Hz and 60-Hz line cycle rejection. Signal and reference monitors, a temperature sensor, and CRC data verification make data reliability better. The ADS126x are pin compatible devices given in a 5-mm × 5-mm VQFN package and are specified across the –40°C to +125°C temperature range. 2 Applications • • • • • PLC analog input modules Weigh scales and strain-gauge digitizers Temperature, pressure measurement Lab instrumentation Process analytics Device Information(1) PART NUMBER ADS126x PACKAGE VQFN (32) BODY SIZE (NOM) 5.0 mm × 5.0 mm (1) For all available packages, see the package option addendum at the end of the data sheet. Block Diagram REFOUT 5 V (A) 2.5-V Ref ADS1260 ADS1261 Ref Mux 3 V ± 5 V (D) START AIN0 Sensor Excitation AIN1 AIN2 Sensor Test AIN3 Control Ref Monitor RESET PWDN DRDY Buf AIN4 AINCOM Input Mux Level Shift PGA AIN5 Digital Filter Serial Interface and CRC Verification Signal Monitor AIN6 AIN7 CS DIN DOUT/DRDY SCLK Temp Sensor AIN8 AIN9 ADS1261 24-Bit û ADC Supply Monitor GPIO AC-Exc (A) Internal Oscillator Clock Mux CLKIN (D) 1 An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications, intellectual property matters and other important disclaimers. PRODUCTION DATA. ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Table of Contents 1 2 3 4 5 6 7 Features .................................................................. Applications ........................................................... Description ............................................................. Revision History..................................................... Device Comparison Table..................................... Pin Configuration and Functions ......................... Specifications......................................................... 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 1 1 1 2 4 4 6 Absolute Maximum Ratings ...................................... 6 ESD Ratings.............................................................. 6 Recommended Operating Conditions....................... 7 Thermal Information .................................................. 7 Electrical Characteristics........................................... 8 Timing Requirements .............................................. 11 Switching Characteristics ........................................ 12 Typical Characteristics ............................................ 15 8 Parameter Measurement Information ................ 22 9 Detailed Description ............................................ 26 8.1 Noise Performance ................................................. 22 9.1 9.2 9.3 9.4 Overview ................................................................. Functional Block Diagram ....................................... Feature Description................................................. Device Functional Modes........................................ 26 27 28 43 9.5 Programming........................................................... 50 9.6 Register Map........................................................... 59 10 Application and Implementation........................ 72 10.1 Application Information.......................................... 72 10.2 Typical Application ................................................ 76 10.3 Initialization Setup ................................................. 79 11 Power Supply Recommendations ..................... 80 11.1 Power-Supply Decoupling..................................... 80 11.2 Analog Power-Supply Clamp ................................ 80 11.3 Power-Supply Sequencing.................................... 80 12 Layout................................................................... 81 12.1 Layout Guidelines ................................................. 81 12.2 Layout Example .................................................... 81 13 Device and Documentation Support ................. 83 13.1 13.2 13.3 13.4 13.5 13.6 13.7 Documentation Support ........................................ Related Links ........................................................ Receiving Notification of Documentation Updates Community Resources.......................................... Trademarks ........................................................... Electrostatic Discharge Caution ............................ Glossary ................................................................ 83 83 83 83 83 83 83 14 Mechanical, Packaging, and Orderable Information ........................................................... 83 4 Revision History Changes from Revision B (October 2018) to Revision C Page • Changed Figure 14, Offset Voltage Long-Term Drift to include 2000-hour data ................................................................ 15 • Changed Figure 31, Voltage Reference Long-Term Drift to include 2000-hour data ......................................................... 17 • Changed CRC polynomial to correct listing error: changed CRC-8-ATM (HEC): X8 + X2 + X0 + 1 to CRC-8-ATM (HEC): X8 + X2 + X1 + 1 ........................................................................................................................................................ 52 Changes from Revision A (May 2018) to Revision B Page • Added ADS1261 device to data sheet ................................................................................................................................... 1 • Changed ADS1260 device from preview to production data (active)..................................................................................... 1 • Added connection options to NC pins .................................................................................................................................... 5 • Added differential input current specification for gain = 128 in Electrical Characteristics ..................................................... 8 • Added no missing codes specification in Electrical Characteristics ...................................................................................... 8 • Changed integral nonlinearity specification for gain 64 and 128 in Electrical Characteristics ............................................... 8 • Changed integral nonlinearity specification for 40 kSPS mode in Electrical Characteristics ................................................ 8 • Added offset voltage long-term drift in Electrical Characteristics .......................................................................................... 8 • Added note for PSRR calculation in Electrical Characteristics ............................................................................................. 8 • Changed voltage reference inputs specification in Electrical Characteristics based on updated characteristics .................. 9 • Added voltage reference initial error specification for ADS1260B and ADS1261B in Electrical Characteristics .................. 9 • Added voltage reference temperature drift specification for ADS1260B and ADS1261B in Electrical Characteristics ........ 9 • Added voltage reference long-term drift in Electrical Characteristics .................................................................................... 9 • Added voltage reference thermal hysteresis in Electrical Characteristics ............................................................................. 9 • Changed th(SCDO2) specification in Switching Characteristics ............................................................................................... 12 2 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 • Changed tp(SCDO2) specification in Switching Characteristics................................................................................................ 12 • Added Figure 14, Offset Voltage Long-Term Drift................................................................................................................ 15 • Changed Figure 24, Conversion Data Histogram (gain = 4) to 8192 data points ................................................................ 16 • Changed Figure 25, Conversion Data Histogram (gain = 128) to 8192 data points ........................................................... 16 • Changed Figure 27, Integral Nonlinearity vs Temperature based on updated characteristics ........................................... 17 • Changed Figure 28, Integral Nonlinearity Distribution to add gain = 128 ........................................................................... 17 • Changed Figure 29, Integral Nonlinearity vs Reference Voltage to add gain = 64 and 128 ............................................... 17 • Added Figure 30, Voltage Reference vs Temperature for ADS1260B, ADS1261B ............................................................ 17 • Added Figure 31, Voltage Reference Long-Term Drift......................................................................................................... 17 • Changed Figure 32, Reference Input Current vs Reference Voltage based on updated characteristics ............................ 17 • Added Figure 39, CMRR vs Frequency .............................................................................................................................. 19 • Added Figure 40, PSRR vs Frequency ............................................................................................................................... 19 • Added text for Table 2, Effective Resolution (Noise-Free Resolution)................................................................................. 22 • Changed Table 2, Effective Resolution (Noise-Free Resolution) based on updated characteristics................................... 24 Changes from Original (March 2018) to Revision A • Page Changed ADS1261 device from advanced information to production data (active)............................................................... 1 Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 3 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 5 Device Comparison Table CHANNELS (1) PART NUMBER SINGLE-ENDED DIFFERENTIAL ADS1260B (2) 5 ADS1261B ADS1261 (1) (2) VOLTAGE REFERENCE GRADE REFERENCE INPUTS GPIO AC EXCITATION 3 12 ppm/°C max 1 — 10 5 12 ppm/°C max 2 4 10 5 40 ppm/°C max 2 4 Reference inputs, GPIOs, and AC-excitation outputs are multiplexed with the analog input channels. The ADS1260 is available in B grade only. 6 Pin Configuration and Functions RHB Package: ADS1260 VQFN-32 Top View AIN3 AIN4 AIN5 AIN6 AIN7 28 27 26 25 NC 25 29 NC 26 AIN2 NC 27 30 AIN4 28 AIN1 AIN3 29 31 AIN2 30 AIN0 AIN1 31 32 AIN0 32 RHB Package: ADS1261 VQFN-32 Top View AINCOM 1 24 NC AINCOM 1 24 AIN8 CAPP 2 23 NC CAPP 2 23 AIN9 CAPN 3 22 NC CAPN 3 22 NC AVDD 4 21 NC AVDD 4 21 NC AVSS 5 20 NC AVSS 5 20 NC REFOUT 6 19 NC REFOUT 6 19 NC PWDN 7 18 CLKIN PWDN 7 18 CLKIN RESET 8 17 DVDD RESET 8 17 DVDD 4 12 13 14 15 16 DIN DRDY DOUT/DRDY BYPASS DGND 16 DGND 11 15 BYPASS SCLK 14 DOUT/DRDY 10 13 DRDY Not to scale CS 12 DIN 9 11 SCLK Submit Documentation Feedback Thermal Pad START 10 CS START 9 Thermal Pad Not to scale Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Pin Functions PIN NO. TYPE DESCRIPTION ADS1260 ADS1261 1 AINCOM AINCOM Analog input/output 2 CAPP CAPP Analog output PGA output P; connect a 4.7-nF C0G dielectric capacitor across CAPP and CAPN 3 CAPN CAPN Analog output PGA output N; connect a 4.7-nF C0G dielectric capacitor across CAPP and CAPN 4 AVDD AVDD Analog Positive analog power supply 5 AVSS AVSS Analog Negative analog power supply REFOUT Analog output Internal 2.5-V reference output; connect a 10-µF capacitor to AVSS 6 REFOUT Analog input common, IDAC1, IDAC2, VBIAS 7 PWDN PWDN Digital input Power down, active low 8 RESET RESET Digital input Reset, active low 9 START START Digital input Start conversion control, active high 10 CS CS Digital input Serial interface chip select, active low 11 SCLK SCLK Digital Input Serial interface shift clock 12 DIN DIN Digital Input Serial interface data input DRDY DRDY 13 14 DOUT/DRDY DOUT/DRDY Digital output Data ready indicator, active low Digital output Dual function serial interface data output and active-low data ready indicator 15 BYPASS BYPASS Analog output Internal subregulator bypass; connect a 1-µF capacitor to DGND 16 DGND DGND Digital Digital ground 17 DVDD DVDD Digital Digital power supply 18 CLKIN CLKIN Digital input NC NC — ADS1260: No connection. Electrically float or connect to DGND ADS1261: Analog input 9, IDAC1, IDAC2 19-22 1) Internal oscillator: connect to DGND 2) External clock: connect clock input No connection. Electrically float or connect to DGND 23 NC AIN9 Analog input/output 24 NC AIN8 Analog input/output ADS1260: No connection. Electrically float or connect to DGND ADS1261: Analog input 8, IDAC1, IDAC2 25 NC AIN7 Analog input/output ADS1260: No connection. Electrically float or connect to DGND ADS1261: Analog input 7, IDAC1, IDAC2 26 NC AIN6 Analog input/output ADS1260: No connection. Electrically float or connect to DGND ADS1261: Analog input 6, IDAC1, IDAC2 27 NC AIN5 Analog input/output ADS1260: No connection. Electrically float or connect to DGND ADS1261: Analog input 5, IDAC1, IDAC2, GPIO3, ACX2 28 AIN4 AIN4 Analog input/output ADS1260: Analog input 4, IDAC1, IDAC2 ADS1261: Analog input 4, IDAC1, IDAC2, GPIO2, ACX1 29 AIN3 AIN3 Analog input/output ADS1260: Analog input 3, IDAC1, IDAC2 ADS1261: Analog input 3, IDAC1, IDAC2, REFN1, GPIO1, ACX2 30 AIN2 AIN2 Analog input/output ADS1260: Analog input 2, IDAC1, IDAC2 ADS1261: Analog input 2, IDAC1, IDAC2, REFP1, GPIO0, ACX1 31 AIN1 AIN1 Analog input/output Analog input 1, IDAC1, IDAC2, REFN0 32 AIN0 AIN0 Analog input/output Analog input 0, IDAC1, IDAC2, REFP0 Thermal Pad Pad Pad — Exposed thermal pad; Connect to AVSS. Pad must be soldered for mechanical integrity. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 5 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 7 Specifications 7.1 Absolute Maximum Ratings see (1) MIN MAX –0.3 7 AVSS to DGND –3 0.3 DVDD to DGND –0.3 7 AVDD + 0.3 AVDD to AVSS Power-supply voltage Analog input voltage AINx AVSS – 0.3 Digital input voltage CS, SCLK, DIN, DOUT/DRDY, DRDY, START, RESET, PWDN, CLKIN DGND – 0.3 DVDD + 0.3 Input current Continuous, all pins except power-supply pins (2) Temperature (1) (2) –10 Junction, TJ Storage, Tstg –60 UNIT V V V 10 mA 150 °C 150 °C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. Input and output pins are diode-clamped to the internal power supplies. Limit the input current to 10 mA in the event the analog input voltage exceeds AVDD + 0.3 V or AVSS – 0.3 V, or if the digital input voltage exceeds DVDD + 0.3 V or DGND – 0.3 V. 7.2 ESD Ratings VALUE V(ESD) (1) (2) 6 Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) ±2000 Charged-device model (CDM), per JEDEC specification JESD22-C101 (2) ±500 UNIT V JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process. Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 7.3 Recommended Operating Conditions MIN NOM MAX AVDD to AVSS 4.75 5 5.25 AVSS to DGND –2.6 0 DVDD to DGND 2.7 5.25 UNIT POWER SUPPLY Analog power supply Digital power supply V V ANALOG INPUTS V(AINx) Absolute input voltage VIN Differential input voltage PGA mode PGA bypassed See Equation 5 AVSS – 0.1 VIN = VAINp – VAINn V AVDD + 0.1 ±VREF / Gain See (1) V VOLTAGE REFERENCE INPUTS VREF Differential reference voltage 0.9 AVDD – AVSS V V(REFNx) Negative reference voltage VREF = V(REFPx) – V(REFNx) AVSS – 0.05 V(REFPx) – 0.9 V V(REFPx) Positive reference voltage V(REFNx) + 0.9 AVDD + 0.05 V EXTERNAL CLOCK fCLK Frequency 2.5 SPS to 25.6 kSPS 1 7.3728 8 40 kSPS 1 10.24 10.75 Duty cycle MHz 40% 60% AVSS AVDD V DGND DVDD V –45 125 °C GENERAL-PURPOSE INPUTS/OUTPUTS (GPIOs) Input voltage DIGITAL INPUTS (Other Than GPIOs) Input voltage TEMPERATURE TA (1) Operating ambient temperature In PGA mode, the maximum differential input voltage is ±(AVDD – AVSS – 0.6 V) / Gain, when operating with VREF ≥ AVDD – AVSS – 0.6 V. 7.4 Thermal Information ADS126x THERMAL METRIC (1) RHB (VQFN) UNIT 32 PINS RθJA Junction-to-ambient thermal resistance 28.6 °C/W RθJC(top) Junction-to-case (top) thermal resistance 17.0 °C/W RθJB Junction-to-board thermal resistance 9.7 °C/W ψJT Junction-to-top characterization parameter 0.2 °C/W ψJB Junction-to-board characterization parameter 9.7 °C/W RθJC(bot) Junction-to-case (bottom) thermal resistance 0.7 °C/W (1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application report. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 7 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 7.5 Electrical Characteristics minimum and maximum specifications apply from TA = –40°C to +125°C; typical specifications are at TA = 25°C; all specifications are at AVDD = 5 V, AVSS = 0 V, DVDD = 3.3 V, VREF = 2.5 V, fCLK = 7.3728 MHz, PGA mode, gain = 1, and data rate = 20 SPS (unless otherwise noted) PARAMETER TEST CONDITIONS MIN TYP MAX 4 6 UNIT ANALOG INPUTS Absolute input current PGA mode, V(AINx) = 2.5 V PGA bypass 200 Absolute input current drift 0.01 PGA mode, VIN = 19 mV Differential input current nA/°C ±0.1 PGA mode, VIN = 2.5 V –3 PGA mode, chop mode (1) ±1 3 ±5 PGA bypass, VIN = 2.5 V nA ±40 Differential input current drift Differential input impedance nA 0.05 PGA mode PGA bypass Crosstalk nA/°C 1 GΩ 50 MΩ 0.1 µV/V PGA Gain settings Antialias filter frequency 1, 2, 4, 8, 16, 32, 64, 128 CCAPP, CAPN = 4.7 nF V/V 60 kHz PERFORMANCE Resolution DR No missing codes 24 Data rate Noise performance INL Integral nonlinearity Offset voltage ±2 10 Gain = 32 to 128 –12 ±3 12 Gain = 1 to 32 (40 kSPS) –15 ±5 15 –175 / gain – 5 ±50 / gain 175 / gain + 5 –0.5 / gain – 0.05 ±0.2 / gain 0.5 / gain + 0.05 TA = 25°C, chop mode Gain = 16 to 128 Chop mode, gain = 1 to 128 GE Gain error Gain drift NMRR Normal-mode rejection ratio (2) CMRR Common-mode rejection ratio (3) PSRR Power-supply rejection ratio (4) Gain = 1, 1000 hr TA = 25°C, gain = 1 to 128 ppmFSR µV On the level of noise Gain = 1 to 8 Offset voltage long-term drift SPS See Table 1 –10 After calibration Offset voltage drift 40000 Gain = 1 to 16 TA = 25°C VOS Bits 2.5 100 / gain 350 / gain 10 50 1 5 ±0.1 –0.5% After calibration ±0.05% nV/°C µV 0.5% On the level of noise Gain = 1 to 128 0.5 4 ppm/°C See Table 7 Data rate = 20 SPS 130 Data rate = 400 SPS AVDD and AVSS DVDD 105 115 85 100 100 120 dB dB INTERNAL OSCILLATOR fCLK Frequency 2.5 SPS to 25.6 kSPS 7.3728 40 kSPS Accuracy (1) (2) (3) (4) 8 MHz 10.24 –2% ±0.5% 2% Chop-mode input current scales with data rate. Normal-mode rejection ratio performance depends on the digital filter configuration. Common-mode rejection ratio is specified at 60 Hz. Power-supply rejection ratio specified at dc. PSRR (dB) = 20 Log (Δ power supply voltage / Δ offset voltage). Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Electrical Characteristics (continued) minimum and maximum specifications apply from TA = –40°C to +125°C; typical specifications are at TA = 25°C; all specifications are at AVDD = 5 V, AVSS = 0 V, DVDD = 3.3 V, VREF = 2.5 V, fCLK = 7.3728 MHz, PGA mode, gain = 1, and data rate = 20 SPS (unless otherwise noted) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT VOLTAGE REFERENCE INPUTS Absolute input current ±250 Input current vs voltage Input current drift Input impedance Differential nA 15 nA/V 0.2 nA/°C 30 MΩ INTERNAL VOLTAGE REFERENCE (5) Voltage Initial error Temperature drift 2.5 TA = 25°C, ADS1260B, ADS1261B ±0.1% TA = 25°C, ADS1261 ±0.2% TA = 0°C to +85°C, ADS1260B, ADS1261B 2 9 TA = –40°C to +125°C, ADS1260B, ADS1261B 4 12 10 40 TA = –40°C to +125°C, ADS1261 Long-term drift Thermal hysteresis (6) 1000 hr ±25 First temperature cycle ±70 Second temperature cycle ±20 Output current Settling time to ±0.001% of final value ppm/°C ppm ppm –10 Load regulation Start-up time V ±0.2% 10 mA 50 µV/mA 100 ms EXCITATION CURRENT SOURCES (IDACS) 50, 100, 250, 500, 750, 1000, 1500, 2000, 2500, 3000 Current settings Compliance range AVSS Accuracy Match error Temperature drift Same current magnitudes µA AVDD – 1.1 –4% ±0.7% 4% –1% ±0.1% 1% Different current magnitudes V ±1% Absolute 50 Match drift, IIDAC1 = IIDAC2 5 25 ppm/°C LEVEL-SHIFT VOLTAGE (VBIAS) Voltage (AVDD + AVSS) / 2 V 100 Ω Output impedance BURN-OUT CURRENT SOURCES Current settings Sink and source Accuracy 0.05-µA range 0.05, 0.2, 1, 10 0.025 0.05 µA 0.075 µA TEMPERATURE SENSOR Sensor voltage TA = 25°C Temperature coefficient 122.4 mV 420 µV/°C MONITORS PGA output Reference voltage (5) (6) Low AVSS + 0.2 High AVDD – 0.2 Low 0.4 V 0.6 V Soldered to PCB using recommended PCB layout pattern and using reflow profile per JEDEC standard J-STD-020D.1 Voltage reference hysteresis measured by operating the device at 25°C cycling the device to 0°C and 105°C and returning the device to 25°C. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 9 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Electrical Characteristics (continued) minimum and maximum specifications apply from TA = –40°C to +125°C; typical specifications are at TA = 25°C; all specifications are at AVDD = 5 V, AVSS = 0 V, DVDD = 3.3 V, VREF = 2.5 V, fCLK = 7.3728 MHz, PGA mode, gain = 1, and data rate = 20 SPS (unless otherwise noted) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT GENERAL-PURPOSE INPUTS/OUTPUTS (GPIOs) (7) VOL Low-level output voltage IOL = –1 mA VOH High-level output voltage IOH = 1 mA VIL Low-level input voltage VIH High-level input voltage 0.2 · AVDD 0.8 · AVDD V 0.3 · AVDD 0.7 · AVDD Input hysteresis V V V 0.5 V DIGITAL INPUTS/OUTPUTS (Other Than GPIOs) VOL Low-level output voltage VOH High-level output voltage VIL Low-level input voltage VIH High-level input voltage IOL = –1 mA 0.2 · DVDD IOL = –8 mA IOH = 1 mA 0.2 · DVDD 0.8 · DVDD IOH = 8 mA Input leakage V 0.75 · DVDD 0.3 · DVDD 0.7 · DVDD Input hysteresis V V 0.1 VIH or VIL V –10 V 10 µA POWER SUPPLY IAVDD, IAVSS Analog supply current PGA bypass 2.7 4.5 PGA mode, gain = 1 to 32 3.8 6 PGA mode, gain = 64 or 128 4.3 6.5 2 8 Power-down mode IAVDD, IAVSS Analog supply current (by function) Voltage reference 0.2 40-kSPS mode 0.5 Current sources IDVDD PD Digital supply current Power dissipation (7) (8) GPIO voltage with respect to AVSS. CLKIN input stopped. 10 Submit Documentation Feedback mA µA mA As programmed 20 SPS 0.4 0.65 40 kSPS 0.6 0.85 Power-down mode (8) 30 50 PGA mode 20 32 Power-down mode 0.1 0.2 mA µA mW Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 7.6 Timing Requirements over operating ambient temperature range, DVDD = 2.7 V to 5.25 V, and DOUT/DRDY load: 20 pF || 100 kΩ to DGND (unless otherwise noted); see Figure 8 MIN MAX UNIT SERIAL INTERFACE td(CSSC) Delay time, first SCLK rising edge after CS falling edge (1) 50 ns tsu(DI) Setup time, DIN valid before SCLK falling edge 25 ns th(DI) Hold time, DIN valid after SCLK falling edge 25 tc(SC) SCLK period (2) 97 tw(SCH), tw(SCL) Pulse duration, SCLK high or low 40 ns td(SCCS) Delay time, last SCLK falling edge before CS rising edge 50 ns tw(CSH) Pulse duration, CS high to reset interface 25 td(SCIR) Delay time, SCLK high or low to force interface auto-reset ns 106 ns ns 65540 1/fCLK RESET tw(RSTL) Pulse duration, RESET low 4 1/fCLK CONVERSION CONTROL tw(STH) Pulse duration, START high 4 1/fCLK tw(STL) Pulse duration, START low 4 1/fCLK tsu(DRST) Setup time, START low or STOP command after DRDY low to stop next conversion (continuous mode) th(DRSP) Hold time, START low or STOP command after DRDY low to continue next conversion (continuous mode) (1) (2) . 100 150 1/fCLK 1/fCLK CS can be tied low. Serial interface time-out mode: minimum SCLK frequency = 1 kHz. Otherwise, no minimum SCLK frequency. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 11 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 7.7 Switching Characteristics over operating ambient temperature range, DVDD = 2.7 V to 5.25 V, and DOUT/DRDY load: 20 pF || 100 kΩ to DGND (unless otherwise noted); see Figure 8 PARAMETER MIN TYP MAX UNIT tw(DRH) Pulse duration, DRDY high 16 tp(CSDO) Propagation delay time, CS falling edge to DOUT/DRDY driven tp(SCDO1) Propagation delay time, SCLK rising edge to valid DOUT/DRDY th(SCDO1) Hold time, SCLK rising edge to invalid data on DOUT/DRDY th(SCDO2) Hold time, last SCLK falling edge of operation to invalid data on DOUT/DRDY tp(SCDO2) Propagation delay time, last SCLK falling edge to valid data ready function on DOUT/DRDY 110 ns tp(CSDOZ) Propagation delay time, CS rising edge to DOUT/DRDY high impedance 50 ns SERIAL INTERFACE 1/fCLK 0 50 ns 40 ns 0 ns 15 ns RESET tp(RSCN) Propagation delay time, RESET rising edge or RESET command to start of conversion tp(PRCM) Propagation delay time, power-on threshold voltage to ADC communication tp(CMCN) Propagation delay time, ADC communication to conversion start 512 1/fCLK 216 1/fCLK 512 1/fCLK AC EXCITATION td(ACX) Delay time, phase-to-phase blanking period tc(ACX) ACX period 8 1/fCLK 2 tSTDR CONVERSION CONTROL tp(STDR) Propagation delay time, START high or START command to DRDY high 2 1/fCLK tw(CSH) CS td(CSSC) tc(SC) td(SCCS) tw(SCH) SCLK th(DI) tsu(DI) tw(SCL) DIN Figure 1. Serial Interface Timing Requirements 12 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 tw(DRH) DRDY CS SCLK tp(SCDO2) tp(SCDO1) tp(CSDO) DRDY DOUT/DRDY (1) tp(CSDOZ) (1) (1) DATA DRDY th(SCDO1) th(SCDO2) Before the first SCLK rising edge and after the last SCLK falling edge of a command, the function of DOUT/DRDY is data ready. Figure 2. Serial Interface Switching Characteristics Serial Interface Auto-Reset td(SCIR) Next byte transaction b7 SCLK b6 b5 b4 b3 b2 b1 b0 Figure 3. Serial Interface Auto-Reset Characteristics tw(STH) START tw(STL) Serial Command START STOP tp(STDR) STOP tsu(DRST) DRDY th(DRSP) Figure 4. Conversion Control Timing Requirements Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 13 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com DVDD 1 V (typ) VBYPASS 1 V (typ) AVDD - AVSS 3.5 V (typ) All supplies reach thresholds DRDY DOUT/DRDY Begin ADC Communication tp(PRCM) tp(CMCN) Conversion Status Start of 1st Conversion Figure 5. Power-Up Characteristics tw(RSTL) RESET Reset Command tp(RSCN) Conversion Status Reset Start Figure 6. RESET pin and RESET Command Timing Requirements tc(ACX) td(ACX) td(ACX) ACX1 ACX1 ACX2 ACX2 Figure 7. AC-Excitation Timing Characteristics DVDD ½ DVDD 50% DGND td, th, tp, tw,tc Figure 8. Timing Voltage-Level Reference 14 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 7.8 Typical Characteristics at TA = 25°C, AVDD = 5 V, AVSS = 0 V, DVDD = 3.3 V, VREF = 2.5 V, data rate = 20 SPS, fCLK = 7.3728 MHz (fCLK = 10.24 MHz for data rate = 40 kSPS), and gain = 1 (unless otherwise noted) 10 0.5 PGA Bypass Gain = 1 Gain = 2 8 Gain = 32 Gain = 64 Gain = 128 PGA Bypass Gain = 1 Gain = 2 0.4 0.3 Offset Voltage (PV) 4 2 0 -2 -4 -6 -8 0.1 0 -0.1 -0.2 -0.4 -20 0 20 40 60 Temperature (qC) 80 100 -0.5 -40 120 -20 0 20 40 60 Temperature (qC) D009 After calibration, shorted input 80 100 120 D010 Chop mode, after calibration, shorted input Figure 9. Offset Voltage vs Temperature Figure 10. Offset Voltage vs Temperature 100 100 Gain = 1 Gain = 16 Gain = 128 90 80 Gain = 1 Gain = 16 Gain = 128 90 80 70 50 Input-Referred Offset Drift (nV/qC) 3.6 3 3.3 2.7 2.4 2.1 0 240 220 200 180 160 140 120 100 80 60 0 40 10 0 20 20 10 0 30 20 1.8 40 30 1.5 40 1.2 50 60 0.9 60 0.6 Population (%) 70 Population (%) Gain = 32 Gain = 64 Gain = 128 -0.3 -10 -40 Input-Referred Offset Drift (nV/qC) D012 Shorted input, 30 units D011 Chop mode, shorted input, 30 units Figure 11. Offset Voltage Drift Distribution Figure 12. Offset Voltage Drift Distribution 2 40 30 25 20 Offset Voltage Long-Term Drift (PV) Gain = 1, 400 SPS Gain = 1, 40000 SPS Gain = 16, 400 SPS Gain = 16, 40000 SPS Gain = 128, 400 SPS Gain = 128, 40000 35 Offset Voltage (PV) Gain = 4 Gain = 8 Gain = 16 0.2 0.3 Offset Voltage (PV) 6 Gain = 4 Gain = 8 Gain = 16 15 10 5 0 -5 -10 0.5 1.5 1 0.5 0 -0.5 -1 -1.5 -2 1 1.5 2 2.5 3 V REF (V) 3.5 4 4.5 5 0 250 D001 After calibration 500 750 1000 1250 Time (hr) 1500 1750 2000 D205 After calibration, gain = 1 Figure 13. Offset Voltage vs Reference Voltage Figure 14. Offset Voltage Long-Term Drift Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 15 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Typical Characteristics (continued) at TA = 25°C, AVDD = 5 V, AVSS = 0 V, DVDD = 3.3 V, VREF = 2.5 V, data rate = 20 SPS, fCLK = 7.3728 MHz (fCLK = 10.24 MHz for data rate = 40 kSPS), and gain = 1 (unless otherwise noted) 50 200 PGA Bypass Gain = 1 Gain = 2 Gain = 32 Gain = 64 Gain = 128 100 50 0 30 20 10 -50 0.45 Input-Referred Noise (PVRMS ) Gain Error (ppm) 40 30 20 10 0 -10 -20 -30 0.4 Gain = 1 Gain = 2 Gain = 4 Gain = 8 2.4 2.2 2 Gain = 16 Gain = 32 Gain = 64 Gain = 128 0.35 0.3 0.25 0.2 0.15 0.1 0.05 1 1.5 2 2.5 3 VREF (V) 3.5 4 4.5 0 -40 5 -20 0 D002 After calibration 20 40 60 Temperature (qC) 80 100 120 D003 Exce 20 SPS, Sinc4 Figure 17. Gain Error vs Reference Voltage Figure 18. Noise vs Temperature 10 50 Gain = 1 Gain = 2 Gain = 4 Gain = 8 Gain = 16 Gain = 32 Gain = 64 Gain = 128 45 Input-Referred Noise (PVRMS ) Input-Referred Noise (PVRMS ) 1.8 0.5 Gain = 1, 400 SPS Gain = 1, 40000 SPS Gain = 128, 400 SPS Gain = 128, 40000 SPS 50 7 6 5 4 3 2 40 30 25 20 15 10 5 0 -40 0 -40 0 20 40 60 Temperature (qC) 80 100 120 -20 0 D004 20 40 60 Temperature (qC) 80 100 120 D005 40000 SPS, Sinc5 Figure 19. Noise vs Temperature Submit Documentation Feedback Gain = 16 Gain = 32 Gain = 64 Gain = 128 35 1 -20 Gain = 1 Gain = 2 Gain = 4 Gain = 8 7200 SPS, Sinc1 16 1.6 Figure 16. Gain Error Drift Distributions 60 8 D013 30 units Figure 15. Gain Error vs Temperature 9 1.4 Gain Drift (ppm/qC) D014 After calibration -40 0.5 1.2 120 1 100 0.8 80 0.6 20 40 60 Temperature (qC) 0.4 0 0 0 -20 0.2 -100 -40 Gain = 1 Gain = 8 Gain = 128 40 Population (%) Gain Error (ppm) 150 Gain = 4 Gain = 8 Gain = 16 Figure 20. Noise vs Temperature Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Typical Characteristics (continued) at TA = 25°C, AVDD = 5 V, AVSS = 0 V, DVDD = 3.3 V, VREF = 2.5 V, data rate = 20 SPS, fCLK = 7.3728 MHz (fCLK = 10.24 MHz for data rate = 40 kSPS), and gain = 1 (unless otherwise noted) 140 Gain = 1, 400 SPS Gain = 128, 400 SPS Gain = 1, 7200 SPS Gain = 128, 7200 SPS Gain = 1, 40000 SPS Gain = 128, 40000 SPS Population (# of Data Points) Input-Referred Noise (PVRMS ) 800 100 10 1 120 100 80 60 40 20 0.5 0.4 D006 0.3 0 5 0.2 4.5 0.1 4 0 3.5 -0.1 2.5 3 V REF (V) -0.2 2 -0.3 1.5 -0.4 1 -0.5 0.07 0.5 D028 Conversion Data (PV) 20 SPS, gain = 4, 256 data points Figure 22. Conversion Data Histogram 140 3000 12 10 8 6 4 -12 0.25 0.2 0.15 0.1 0.05 -0.1 0 0 -0.05 0 -0.15 500 -0.2 20 2 1000 0 40 1500 -2 60 2000 -4 80 -6 100 2500 -8 120 -10 Population (# of Data Points) 160 3500 -0.25 Population (# of Data Points) Figure 21. Noise vs Reference Voltage Conversion Data (PV) D029 Conversion Data (PV) D030 7200 SPS, gain = 4, 8192 data points 20 SPS, gain = 128, 256 data points Figure 24. Conversion Data Histogram 4000 10 3500 8 Linearity Error (ppmFSR) Population (# of Data Points) Figure 23. Conversion Data Histogram 3000 2500 2000 1500 1000 Gain = 1 Gain = 4 Gain = 16 Gain = 32 Gain = 64 6 4 2 0 -2 -4 -6 500 -8 Conversion Data (PV) -10 -100 -80 3 2.5 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -3 -2.5 0 -60 D031 -40 -20 0 20 40 Full Scale Range (%VIN) 60 80 100 D033 7200 SPS, gain = 128, 8192 data points Figure 25. Conversion Data Histogram Figure 26. Integral Nonlinearity vs VIN Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 17 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Typical Characteristics (continued) at TA = 25°C, AVDD = 5 V, AVSS = 0 V, DVDD = 3.3 V, VREF = 2.5 V, data rate = 20 SPS, fCLK = 7.3728 MHz (fCLK = 10.24 MHz for data rate = 40 kSPS), and gain = 1 (unless otherwise noted) 50 10 Gain = 1 Gain = 4 Gain = 128 8 40 7 35 6 5 4 30 25 20 3 15 2 10 1 5 6 5.5 5 4 4.5 3 3.5 120 2 100 2.5 80 1 20 40 60 Temperature (qC) 1.5 0 0 0 -20 0.5 0 -40 Gain = 1 Gain = 4 Gain = 32 Gain = 128 45 Population (%) Integral Non-Linearity (ppm FSR) 9 Gain = 16 Gain = 64 Integral Non-Linearity (ppmFSR) D007 D015 30 Units Figure 27. Integral Nonlinearity vs Temperature Figure 28. Integral Nonlinearity Distribution 2.4985 Gain = 1, 20 SPS Gain = 4, 20 SPS Gain = 32, 20 SPS Gain = 64, 20 SPS Gain = 128, 20 SPS 16 Gain = 1, 40000 SPS Gain = 4, 40000 SPS Gain = 32, 40000 SPS 2.498 Reference Voltage (V) Integral Non-Linearity (ppmFSR) 20 12 Data for gains 64, 128 limited by instrument noise for VREF < 2 V 8 2.4975 2.497 2.4965 2.496 2.4955 4 2.495 0 0.5 1 1.5 2 2.5 3 VREF (V) 3.5 4 4.5 2.4945 -40 5 -20 D008 0 20 40 60 Temperature (qC] 80 100 120 D102 ADS1260B, ADS1261B - 30 units Figure 29. Integral Nonlinearity vs Reference Voltage Figure 30. Voltage Reference vs Temperature 350 300 50 Reference Input Current (nA) Reference Long-Term Drift Error (ppm) 75 25 0 -25 -50 IREFP , T A IREFP , T A IREFP , T A IREFP , T A = -40qC = 25qC = 85qC = 125qC 0 250 500 750 1000 1250 Time (hr) 1500 1750 2000 150 100 50 -50 0.5 REFN 1 1.5 2 2.5 3 3.5 4 Differential Reference Voltage (V) D204 4.5 5 D024 IREFP measured with VREFN = AVSS IREFN measured with VREFP = AVDD After calibration, 30 units Figure 31. Voltage Reference Long-Term Drift Submit Documentation Feedback REFP 200 0 -75 18 250 IREFN , T A = -40qC IREFN , T A = 25qC IREFN , T A = 85qC IREFN , T A = 125qC Figure 32. Reference Input Current vs Reference Voltage Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Typical Characteristics (continued) at TA = 25°C, AVDD = 5 V, AVSS = 0 V, DVDD = 3.3 V, VREF = 2.5 V, data rate = 20 SPS, fCLK = 7.3728 MHz (fCLK = 10.24 MHz for data rate = 40 kSPS), and gain = 1 (unless otherwise noted) 40 Internal Oscillator Error (%) 1 Population (%) 30 20 10 124.2 123.8 123.4 123 122.6 122.2 121.8 121.4 121 0 0.5 0 -0.5 -1 -1.5 -40 D017 -20 0 Temperature Sensor Voltage (mV) 100 120 D016 Figure 34. Internal Oscillator vs Temperature Figure 33. Temperature Sensor Voltage Histogram 6 5 IDVDD (20 SPS) IDVDD (40000 SPS) PGA High Monitor Threshold (V) IAVDD , I AVSS (Gain d 32) IAVDD , I AVSS (Gain t 64) 5 Operating Current (mA) 80 30 units 30 units 4 3 2 1 0 -40 -20 0 20 40 60 Temperature (qC) 80 100 4.95 4.9 4.85 4.8 4.75 4.7 -40 120 0 20 40 60 Temperature (qC) 80 100 120 D025 Figure 36. PGA High Monitor Threshold 1 Reference Low Monitor Threshold (V) 0.3 0.25 0.2 0.15 0.1 0.05 0 -40 -20 D018 Figure 35. Operating Current vs Temperature PGA Low Monitor Threshold (V) 20 40 60 Temperature (qC) -20 0 20 40 60 Temperature (qC) 80 100 120 0.8 0.6 0.4 0.2 0 -40 -20 D026 Figure 37. PGA Low Monitor Threshold 0 20 40 60 Temperature (qC) 80 100 120 D027 Figure 38. Reference Voltage Low Alarm Threshold Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 19 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Typical Characteristics (continued) at TA = 25°C, AVDD = 5 V, AVSS = 0 V, DVDD = 3.3 V, VREF = 2.5 V, data rate = 20 SPS, fCLK = 7.3728 MHz (fCLK = 10.24 MHz for data rate = 40 kSPS), and gain = 1 (unless otherwise noted) 125 Power-Supply Rejection Ratio (dB) Common Mode Rejection Ratio (dB) 135 120 105 90 75 60 120 115 110 105 100 95 90 AVDD DVDD 85 80 1 10 100 1000 10000 Frequency (Hz) 100000 1000000 1 10 100 D150 Data rate = 1200 SPS 1000 10000 Frequency (Hz) 100000 1000000 D151 Data rate = 1200 SPS Figure 39. CMRR vs Frequency Figure 40. PSRR vs Frequency 55 130 125 52.5 115 IDAC Current (PA) CMRR and PSRR (dB) 120 110 105 100 95 90 CMRR PSRR AVDD, AVSS PSRR DVDD 85 80 -40 50 47.5 45 TA = -40qC TA = 25qC TA = 85qC TA = 125qC 42.5 40 -20 0 20 40 60 Temperature (qC) 80 100 120 0 0.5 1 1.5 2 2.5 3 IDAC Voltage (V) D034 3.5 4 4.5 5 D022 IIDAC = 50 µA Figure 41. CMRR and PSRR vs Temperature Figure 42. IDAC Current vs IDAC Voltage 260 1050 1000 IDAC Current (PA) IDAC Current (PA) 250 240 230 220 TA = -40qC TA = 25qC TA = 85qC TA = 125qC 210 950 900 TA = -40qC TA = 25qC TA = 85qC TA = 125qC 850 200 800 0 0.5 1 1.5 2 2.5 3 IDAC Voltage (V) 3.5 4 4.5 5 0 0.5 1 D019 IIDAC = 250 µA Submit Documentation Feedback 2 2.5 3 IDAC Voltage (V) 3.5 4 4.5 5 D020 IIDAC = 1000 µA Figure 43. IDAC Current vs IDAC Voltage 20 1.5 Figure 44. IDAC Current vs IDAC Voltage Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Typical Characteristics (continued) at TA = 25°C, AVDD = 5 V, AVSS = 0 V, DVDD = 3.3 V, VREF = 2.5 V, data rate = 20 SPS, fCLK = 7.3728 MHz (fCLK = 10.24 MHz for data rate = 40 kSPS), and gain = 1 (unless otherwise noted) 3050 0.2 TA = -40qC TA = 25qC TA = 85qC TA = 125qC 0.15 IDAC Match Error (%) IDAC Current (PA) 3000 2950 2900 TA = -40qC TA = 25qC TA = 85qC TA = 125qC 2850 0.1 0.05 0 -0.05 -0.1 -0.15 2800 -0.2 0 0.5 1 1.5 2 2.5 3 IDAC Voltage (V) 3.5 4 4.5 5 0 0.5 1 1.5 D021 IIDAC = 3000 µA 2 2.5 3 IDAC Voltage (V) 3.5 4 4.5 5 D023 IIDAC1 = IIDAC2 = 250 µA Figure 45. IDAC Current vs IDAC Voltage Figure 46. IDAC Current Match vs IDAC Voltage 0.2 TA = -40qC TA = 25qC TA = 85qC TA = 125qC IDAC Match Error (%) 0.15 0.1 0.05 0 -0.05 -0.1 -0.15 -0.2 0 0.5 1 1.5 2 2.5 3 IDAC Voltage (V) 3.5 4 4.5 5 D035 IIDAC1 = IIDAC2 = 1000 µA Figure 47. IDAC Current Match vs IDAC Voltage Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 21 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 8 Parameter Measurement Information 8.1 Noise Performance The ADS126x noise performance depends on the ADC configuration: data rate, PGA gain, digital filter configuration, and chop mode. The combination of the parameters affect noise performance. Two significant factors affecting noise performance are data rate and PGA gain. Since the profile of noise is predominantly white (flat vs frequency), decreasing the data rate proportionally decreases bandwidth and therefore, total noise. Since the noise of the PGA is lower than that of the modulator of the ADC, increasing the gain reduces noise when treated as an input-referred quantity. Noise performance also depends on the digital filter and chop mode. As the order of the digital filter increases, the noise bandwidth correspondingly decreases resulting in lower noise. Further, as a result of two-point data averaging in chop mode, noise performance improves by √2 compared to normal operation. Table 1 shows noise performance in units of μVRMS (RMS = root mean square) under the conditions listed. The values in parenthesis are peak-to-peak values. Table 2 shows the noise performance in effective resolution (bits) under the specified conditions. The values shown in parenthesis are the noise-free resolution. Noise-free resolution is the resolution of the ADC with no code flicker. The noise-free resolution data are calculated based on the peak-to-peak noise measurements. The effective resolution data listed in the tables are calculated using Equation 1: Effective Resolution or Noise-Free Resolution = ln (FSR / en) / ln (2) where • • FSR = full scale range = 2 · VREF / Gain (See Recommended Operating Conditions for FSR) en = Input referred voltage noise (RMS value to calculate effective resolution, p-p value to calculate noise-free resolution) (1) The data shown in the noise performance table represent typical ADC performance at TA = 25°C. The noiseperformance data are the standard deviation and peak-to-peak computations of the ADC data. The noise data are acquired with inputs shorted, based on consecutive ADC readings for a period of ten seconds or 8192 data points, whichever occurs first. Because of the statistical nature of noise, repeated noise measurements may yield higher or lower noise performance results. As a result of the increased full-scale input range provided by 5-V reference operation, effective resolution and noise-free resolution performance are typically optimized using a 5-V reference. The effective resolution and noise-free resolution performance data shown in Table 2 are with external 5-V reference operation. Table 1. Noise in µVRMS (µVPP) at TA = 25°C and Internal 2.5-V Reference DATA RATE FILTER (SPS) GAIN 1 2 4 8 16 32 64 128 2.5 FIR 0.18 (0.6) 0.078 (0.28) 0.046 (0.16) 0.025 (0.096) 0.014 (0.053) 0.012 (0.045) 0.01 (0.042) 0.01 (0.04) 2.5 Sinc1 0.15 (0.47) 0.071 (0.28) 0.038 (0.14) 0.019 (0.075) 0.012 (0.051) 0.01 (0.039) 0.009 (0.037) 0.009 (0.037) 2.5 Sinc2 0.14 (0.38) 0.065 (0.23) 0.032 (0.096) 0.018 (0.059) 0.011 (0.037) 0.007 (0.028) 0.007 (0.028) 0.008 (0.033) 2.5 Sinc3 0.12 (0.38) 0.062 (0.17) 0.028 (0.064) 0.016 (0.053) 0.01 (0.035) 0.008 (0.027) 0.007 (0.026) 0.006 (0.023) 2.5 Sinc4 0.1 (0.26) 0.059 (0.17) 0.032 (0.085) 0.016 (0.059) 0.010 (0.035) 0.008 (0.027) 0.006 (0.025) 0.006 (0.024) 5 FIR 0.22 (0.89) 0.11 (0.4) 0.058 (0.24) 0.032 (0.13) 0.021 (0.085) 0.016 (0.065) 0.014 (0.061) 0.015 (0.066) 5 Sinc1 0.18 (0.6) 0.093 (0.36) 0.047 (0.17) 0.025 (0.11) 0.017 (0.069) 0.014 (0.061) 0.012 (0.054) 0.014 (0.063) 5 Sinc2 0.16 (0.64) 0.084 (0.32) 0.043 (0.16) 0.023 (0.085) 0.015 (0.064) 0.011 (0.047) 0.010(0.046) 0.011 (0.049) 5 Sinc3 0.13 (0.51) 0.088 (0.32) 0.036 (0.15) 0.024 (0.091) 0.014 (0.053) 0.01 (0.043) 0.009 (0.045) 0.009 (0.042) 5 Sinc4 0.13 (0.51) 0.077 (0.28) 0.034 (0.12) 0.021 (0.075) 0.013 (0.053) 0.010 (0.044) 0.008 (0.038) 0.009 (0.038) 10 FIR 0.27 (1.4) 0.14 (0.72) 0.076 (0.4) 0.042 (0.21) 0.029 (0.15) 0.023 (0.12) 0.023 (0.11) 0.022 (0.11) 10 Sinc1 0.23 (1.1) 0.13 (0.57) 0.064 (0.3) 0.036 (0.19) 0.024 (0.13) 0.02 (0.1) 0.018 (0.083) 0.018 (0.089) 10 Sinc2 0.2 (0.89) 0.11 (0.51) 0.054 (0.24) 0.03 (0.14) 0.019 (0.093) 0.015 (0.075) 0.015 (0.079) 0.016 (0.077) 10 Sinc3 0.18 (0.81) 0.097 (0.38) 0.05 (0.22) 0.028 (0.14) 0.019 (0.088) 0.015 (0.063) 0.013 (0.067) 0.013 (0.065) 10 Sinc4 0.17 (0.68) 0.099 (0.45) 0.049 (0.24) 0.024 (0.12) 0.018 (0.085) 0.013 (0.063) 0.012 (0.061) 0.012 (0.062) 16.6 Sinc1 0.3 (1.4) 0.16 (0.81) 0.082 (0.43) 0.048 (0.25) 0.031 (0.17) 0.025 (0.15) 0.024 (0.12) 0.024 (0.14) 22 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Noise Performance (continued) Table 1. Noise in µVRMS (µVPP) at TA = 25°C and Internal 2.5-V Reference (continued) DATA RATE FILTER (SPS) GAIN 1 2 4 8 16 32 64 128 16.6 Sinc2 0.24 (1.2) 0.13 (0.64) 0.067 (0.34) 0.038 (0.2) 0.026 (0.14) 0.021 (0.11) 0.019 (0.099) 0.019 (0.098) 16.6 Sinc3 0.22 (0.98) 0.12 (0.64) 0.065 (0.3) 0.036 (0.18) 0.024 (0.12) 0.019 (0.095) 0.017 (0.092) 0.018 (0.093) 16.6 Sinc4 0.21 (1.1) 0.12 (0.53) 0.06 (0.29) 0.035 (0.18) 0.022 (0.11) 0.017 (0.084) 0.016 (0.085) 0.016 (0.086) 20 FIR 0.37 (2) 0.2 (1.1) 0.1 (0.56) 0.059 (0.34) 0.041 (0.22) 0.034 (0.18) 0.029 (0.17) 0.03 (0.15) 20 Sinc1 0.32 (1.8) 0.18 (0.92) 0.091 (0.48) 0.051 (0.26) 0.034 (0.2) 0.028 (0.15) 0.025 (0.14) 0.025 (0.14) 20 Sinc2 0.27 (1.4) 0.15 (0.77) 0.073 (0.35) 0.042 (0.22) 0.027 (0.14) 0.022 (0.13) 0.021 (0.11) 0.02 (0.11) 20 Sinc3 0.24 (1.2) 0.13 (0.64) 0.069 (0.35) 0.039 (0.21) 0.026 (0.14) 0.02 (0.11) 0.018 (0.099) 0.018 (0.1) 20 Sinc4 0.23 (1.1) 0.13 (0.66) 0.066 (0.33) 0.037 (0.19) 0.024 (0.12) 0.018 (0.095) 0.017 (0.095) 0.017 (0.099) 50 Sinc1 0.49 (2.9) 0.27 (1.6) 0.14 (0.83) 0.08 (0.5) 0.053 (0.31) 0.043 (0.25) 0.039 (0.23) 0.038 (0.23) 50 Sinc2 0.4 (2.3) 0.22 (1.3) 0.11 (0.69) 0.064 (0.38) 0.043 (0.27) 0.035 (0.22) 0.033 (0.2) 0.032 (0.2) 50 Sinc3 0.37 (2.2) 0.2 (1.2) 0.11 (0.64) 0.058 (0.35) 0.04 (0.25) 0.033 (0.19) 0.029 (0.18) 0.03 (0.18) 50 Sinc4 0.34 (2) 0.19 (1.1) 0.098 (0.61) 0.056 (0.32) 0.036 (0.23) 0.03 (0.17) 0.028 (0.17) 0.028 (0.17) 60 Sinc1 0.55 (3.3) 0.28 (1.9) 0.15 (0.88) 0.087 (0.53) 0.058 (0.34) 0.047 (0.28) 0.044 (0.29) 0.042 (0.26) 60 Sinc2 0.45 (2.7) 0.24 (1.4) 0.12 (0.71) 0.07 (0.45) 0.048 (0.32) 0.039 (0.25) 0.036 (0.21) 0.035 (0.21) 60 Sinc3 0.41 (2.7) 0.21 (1.3) 0.11 (0.68) 0.065 (0.4) 0.044 (0.25) 0.036 (0.23) 0.032 (0.19) 0.031 (0.19) 60 Sinc4 0.37 (2) 0.2 (1.1) 0.11 (0.6) 0.059 (0.36) 0.041 (0.25) 0.033 (0.21) 0.03 (0.18) 0.03 (0.17) 100 Sinc1 0.69 (4.5) 0.37 (2.4) 0.19 (1.3) 0.11 (0.73) 0.075 (0.5) 0.06 (0.39) 0.056 (0.37) 0.056 (0.38) 100 Sinc2 0.56 (3.5) 0.3 (1.9) 0.16 (0.97) 0.09 (0.55) 0.062 (0.39) 0.051 (0.32) 0.046 (0.31) 0.045 (0.29) 100 Sinc3 0.51 (3.4) 0.27 (1.8) 0.14 (0.9) 0.083 (0.51) 0.056 (0.36) 0.045 (0.3) 0.041 (0.27) 0.041 (0.25) 100 Sinc4 0.48 (3.3) 0.26 (1.6) 0.14 (0.87) 0.078 (0.48) 0.053 (0.34) 0.043 (0.27) 0.039 (0.24) 0.039 (0.26) 400 Sinc1 1.4 (9.6) 0.72 (5.4) 0.38 (2.7) 0.22 (1.6) 0.15 (1.1) 0.12 (0.85) 0.11 (0.85) 0.11 (0.79) 400 Sinc2 1.1 (8.2) 0.58 (4.2) 0.31 (2.3) 0.18 (1.3) 0.12 (0.9) 0.099 (0.74) 0.091 (0.65) 0.091 (0.69) 400 Sinc3 1 (7.4) 0.53 (3.7) 0.28 (2) 0.17 (1.2) 0.11 (0.8) 0.09 (0.66) 0.083 (0.61) 0.083 (0.59) 400 Sinc4 0.95 (6.9) 0.51 (3.6) 0.27 (1.9) 0.15 (1.2) 0.1 (0.7) 0.084 (0.58) 0.077 (0.55) 0.077 (0.57) 1200 Sinc1 2.3 (17) 1.2 (9.2) 0.64 (5) 0.37 (2.9) 0.25 (1.9) 0.2 (1.6) 0.19 (1.4) 0.19 (1.5) 1200 Sinc2 1.9 (14) 1 (7.6) 0.54 (3.9) 0.31 (2.4) 0.21 (1.6) 0.17 (1.3) 0.16 (1.2) 0.16 (1.2) 1200 Sinc3 1.8 (13) 0.92 (7) 0.49 (3.7) 0.29 (2.2) 0.19 (1.4) 0.16 (1.2) 0.14 (1.1) 0.14 (1.1) 1200 Sinc4 1.6 (12) 0.86 (6.4) 0.46 (3.6) 0.27 (2) 0.18 (1.4) 0.15 (1.1) 0.13 (1) 0.13 (1) 2400 Sinc1 3.2 (25) 1.7 (13) 0.88 (6.7) 0.51 (3.9) 0.35 (2.7) 0.28 (2.2) 0.26 (2) 0.26 (2) 2400 Sinc2 2.7 (21) 1.4 (10) 0.76 (5.8) 0.44 (3.3) 0.3 (2.2) 0.24 (1.9) 0.22 (1.6) 0.22 (1.6) 2400 Sinc3 2.5 (19) 1.3 (9.8) 0.69 (5.2) 0.4 (3) 0.27 (2.1) 0.22 (1.7) 0.2 (1.6) 0.2 (1.5) 2400 Sinc4 2.3 (17) 1.2 (9.4) 0.65 (4.9) 0.37 (2.8) 0.25 (2) 0.21 (1.5) 0.19 (1.5) 0.19 (1.4) 4800 Sinc1 4.3 (33) 2.3 (17) 1.2 (9.4) 0.69 (5.2) 0.46 (3.5) 0.37 (2.9) 0.34 (2.6) 0.34 (2.6) 4800 Sinc2 3.8 (29) 2 (15) 1.1 (8.5) 0.61 (4.7) 0.41 (3.1) 0.33 (2.6) 0.31 (2.3) 0.3 (2.3) 4800 Sinc3 3.5 (27) 1.8 (14) 0.97 (7.2) 0.56 (4.1) 0.38 (3) 0.31 (2.4) 0.28 (2.1) 0.28 (2.2) 4800 Sinc4 3.3 (25) 1.7 (13) 0.92 (7.1) 0.53 (4.1) 0.36 (2.7) 0.29 (2.2) 0.27 (2.1) 0.27 (1.9) 7200 Sinc1 5 (38) 2.6 (20) 1.4 (10) 0.8 (6) 0.53 (4) 0.43 (3.2) 0.39 (2.9) 0.39 (2.9) 7200 Sinc2 4.6 (35) 2.4 (19) 1.3 (9.9) 0.73 (5.4) 0.49 (3.8) 0.39 (2.9) 0.36 (2.8) 0.36 (2.7) 7200 Sinc3 4.3 (33) 2.2 (17) 1.2 (9.3) 0.68 (5) 0.46 (3.6) 0.37 (2.8) 0.34 (2.5) 0.34 (2.6) 7200 Sinc4 4.1 (31) 2.1 (15) 1.1 (8.8) 0.65 (5) 0.44 (3.3) 0.35 (2.6) 0.33 (2.5) 0.32 (2.5) 14400 Sinc5 6 (47) 3.1 (24) 1.7 (13) 0.93 (7.1) 0.61 (4.9) 0.49 (3.8) 0.45 (3.5) 0.45 (3.4) 19200 Sinc5 8.5 (67) 4.3 (34) 2.3 (17) 1.2 (9.6) 0.77 (6) 0.57 (4.3) 0.54 (4) 0.53 (4.1) 25600 Sinc5 19 (140) 9.5 (73) 4.8 (37) 2.5 (18) 1.3 (10) 0.83 (6.3) 0.8 (6) 0.81 (6) 40000 Sinc5 30 (220) 15 (110) 7.7 (56) 3.9 (29) 2 (15) 1.2 (9.4) 1.2 (8.9) 1.2 (9) Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 23 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Table 2. Effective Resolution (Noise-Free Resolution) at TA = 25°C and External 5-V Reference DATA RATE (SPS) 24 GAIN FILTER 1 2 4 8 16 32 64 128 2.5 FIR 24 (24) 24 (22.8) 24 (23.8) 24 (23.8) 24 (23.8) 24 (22.8) 24 (22) 23 (20.8) 2.5 Sinc1 24 (24) 24 (22.8) 24 (23.8) 24 (23.8) 24 (22.8) 24 (22.8) 24 (22.4) 23.2 (21.2) 2.5 Sinc2 24 (24) 24 (22.8) 24 (23.8) 22.8 (23.8) 21.8 (22.8) 24 (23.8) 24 (22.4) 23.9 (22) 2.5 Sinc3 24 (24) 24 (22.8) 24 (23.8) 22.8 (23.8) 24 (23.8) 24 (23.8) 24 (22.4) 23.8 (22) 2.5 Sinc4 24 (24) 24 (22.8) 24 (23.8) 22.8 (23.8) 24 (23.8) 24 (23.8) 24 (23) 23.5 (22) 5 FIR 24 (23) 24 (22.8) 24 (23.8) 24 (22.8) 24 (22.2) 24 (21.8) 23.6 (21.7) 22.5 (20.7) 5 Sinc1 24 (23.7) 24 (23.8) 24 (23.8) 24 (22.8) 24 (22.2) 24 (22.8) 23.3 (21.4) 22.8 (20.7) 5 Sinc2 24 (24) 24 (23.8) 24 (23.8) 24 (23.8) 24 (23.8) 24 (22.8) 23.7 (21.7) 22.8 (21) 5 Sinc3 24 (24) 24 (23.8) 24 (23.8) 24 (23.8) 24 (23.8) 24 (22.8) 23.5 (21.4) 23.5 (21.7) 5 Sinc4 24 (24) 24 (23.8) 24 (23.8) 22.8 (23.8) 24 (23.8) 24 (23.8) 24 (22) 23.3 (21.2) 10 FIR 24 (22.4) 24 (22.8) 24 (22.8) 24 (22.2) 24 (21.8) 23.5 (21.2) 22.8 (20.5) 22.1 (19.9) 10 Sinc1 24 (23) 24 (22.8) 24 (22.8) 24 (22.8) 24 (22.2) 23.6 (21.2) 23.4 (21.2) 22.3 (19.8) 10 Sinc2 24 (23) 24 (22.8) 24 (22.8) 24 (22.8) 24 (22.2) 24 (22.2) 23.2 (21.4) 22.3 (20.2) 10 Sinc3 24 (24) 24 (22.8) 24 (23.8) 24 (23.8) 24 (22.8) 24 (22.2) 23.3 (21.2) 22.7 (20.7) 10 Sinc4 24 (24) 24 (22.8) 24 (23.8) 24 (22.8) 24 (22.8) 24 (22.2) 23.7 (21.4) 22.9 (20.8) 16.6 Sinc1 24 (22) 24 (21.8) 24 (22.2) 24 (21.8) 23.7 (21.2) 23.4 (21) 22.5 (20.3) 21.8 (19.6) 16.6 Sinc2 24 (22.4) 24 (22.8) 24 (22.2) 24 (22.2) 24 (21.8) 23.7 (21.2) 23 (20.7) 22 (19.5) 16.6 Sinc3 24 (23) 24 (22.8) 24 (22.2) 24 (22.8) 24 (22.8) 23.9 (21.5) 23.1 (21) 22 (19.8) 16.6 Sinc4 24 (23) 24 (22.8) 24 (22.8) 24 (22.8) 24 (22.2) 24 (21.5) 23.4 (20.7) 22.5 (20.1) 20 FIR 24 (22) 23.8 (21.5) 23.9 (21.8) 23.9 (21.5) 23.5 (21) 22.9 (20.5) 22.2 (19.8) 21.3 (18.7) 20 Sinc1 24 (22) 24 (22.2) 24 (21.8) 23.9 (21.8) 23.7 (21.5) 23.3 (21) 22.6 (20.3) 21.5 (19.2) 20 Sinc2 24 (23) 24 (22.2) 24 (22.2) 24 (21.8) 24 (21.8) 23.6 (21.2) 22.8 (20.3) 21.9 (19.6) 20 Sinc3 24 (22.4) 24 (22.8) 24 (22.2) 24 (22.8) 24 (21.8) 23.7 (21.5) 23 (20.7) 21.9 (19.4) 20 Sinc4 24 (23) 24 (22.8) 24 (22.8) 24 (22.2) 24 (22.2) 23.8 (21.2) 23.1 (20.7) 22 (19.4) 50 Sinc1 23.9 (21.4) 23.7 (21.5) 23.7 (21.2) 23.5 (20.8) 23.3 (20.6) 22.6 (20) 21.9 (19.3) 21 (18.6) 50 Sinc2 24 (21.7) 23.9 (21.5) 23.8 (21.2) 23.7 (21.5) 23.5 (20.8) 22.9 (20.2) 22.1 (19.3) 21.2 (18.8) 50 Sinc3 24 (22) 23.9 (21.5) 23.9 (21.5) 23.8 (21) 23.6 (21.2) 23 (20.5) 22.3 (19.8) 21.3 (18.6) 50 Sinc4 24 (22) 24 (21.8) 24 (21.8) 23.9 (21.5) 23.7 (21.2) 23.2 (20.8) 22.4 (20) 21.5 (18.9) 60 Sinc1 23.7 (21.4) 23.6 (21) 23.6 (21.2) 23.4 (20.8) 23.1 (20.5) 22.5 (19.9) 21.8 (19.1) 20.8 (18.2) 60 Sinc2 24 (21.4) 23.8 (21.5) 23.7 (21.2) 23.6 (21.2) 23.4 (20.8) 22.7 (20.2) 22.1 (19.3) 21.2 (18.5) 60 Sinc3 24 (21.7) 23.9 (21.5) 23.9 (21.5) 23.7 (21.2) 23.5 (20.8) 22.9 (20.5) 22.2 (19.5) 21.2 (18.8) 60 Sinc4 24 (22) 24 (21.8) 23.9 (21.5) 23.7 (21.2) 23.4 (20.6) 23 (20.2) 22.2 (19.5) 21.2 (18.7) 100 Sinc1 23.6 (21) 23.4 (20.6) 23.3 (20.5) 23.1 (20.4) 22.8 (20) 22.1 (19.4) 21.4 (18.8) 20.5 (17.7) 100 Sinc2 23.8 (21) 23.6 (21) 23.6 (21) 23.4 (21) 23 (20.2) 22.4 (19.7) 21.7 (19.1) 20.8 (18) 100 Sinc3 23.8 (21.2) 23.6 (21.2) 23.6 (21) 23.5 (21) 23.2 (20.5) 22.5 (19.9) 21.8 (19) 20.8 (17.9) 100 Sinc4 23.9 (21.4) 23.7 (21.2) 23.7 (21.2) 23.6 (21) 23.3 (20.6) 22.6 (19.7) 21.9 (19.4) 21 (18.1) 400 Sinc1 22.8 (19.8) 22.5 (19.7) 22.5 (19.6) 22.3 (19.6) 21.9 (19) 21.2 (18.2) 20.4 (17.6) 19.5 (16.6) 400 Sinc2 23.1 (20.3) 22.8 (20.1) 22.8 (20) 22.6 (19.6) 22.1 (19.2) 21.4 (18.6) 20.7 (17.9) 19.8 (17.1) 400 Sinc3 23.1 (20.4) 22.9 (20) 22.8 (19.9) 22.7 (20) 22.3 (19.4) 21.5 (18.7) 20.8 (17.8) 19.9 (17) 400 Sinc4 23.2 (20.3) 23 (20.2) 22.9 (20.1) 22.7 (20.1) 22.3 (19.5) 21.7 (18.9) 21 (18) 20 (17.2) 1200 Sinc1 22.1 (19.2) 21.8 (19.1) 21.7 (18.9) 21.6 (18.7) 21.1 (18.3) 20.4 (17.5) 19.7 (16.8) 18.8 (15.7) 1200 Sinc2 22.3 (19.5) 22.1 (19.3) 22 (19.1) 21.8 (18.9) 21.4 (18.4) 20.6 (17.7) 20 (17.1) 19 (16) 1200 Sinc3 22.4 (19.6) 22.2 (19.2) 22.1 (19.2) 21.9 (19) 21.5 (18.5) 20.8 (18) 20.1 (17.2) 19.2 (16.2) 1200 Sinc4 22.5 (19.6) 22.3 (19.6) 22.2 (19.2) 22 (19.1) 21.6 (18.7) 20.9 (18) 20.2 (17.3) 19.2 (16.4) 2400 Sinc1 21.6 (18.7) 21.4 (18.3) 21.3 (18.4) 21.1 (18.1) 20.7 (17.7) 19.9 (17.1) 19.2 (16.2) 18.3 (15.4) 2400 Sinc2 21.8 (18.8) 21.6 (18.6) 21.5 (18.6) 21.3 (18.5) 20.9 (18) 20.2 (17.3) 19.5 (16.6) 18.5 (15.6) Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Table 2. Effective Resolution (Noise-Free Resolution) at TA = 25°C and External 5-V Reference (continued) DATA RATE (SPS) FILTER GAIN 2400 2400 1 2 4 8 16 32 64 128 Sinc3 21.9 (19.1) 21.7 (18.8) 21.6 (18.6) 21.4 (18.6) 21 (18.1) 20.3 (17.5) 19.6 (16.7) 18.7 (15.7) Sinc4 22 (19.1) 21.8 (19) 21.8 (19) 21.6 (18.6) 21.1 (18) 20.4 (17.5) 19.7 (16.7) 18.8 (15.9) 4800 Sinc1 21.1 (18.1) 20.9 (17.9) 20.9 (17.9) 20.6 (17.7) 20.2 (17.2) 19.5 (16.6) 18.8 (15.8) 17.9 (14.9) 4800 Sinc2 21.3 (18.4) 21.1 (18.1) 21 (18.1) 20.8 (17.9) 20.4 (17.4) 19.7 (16.6) 19 (16.1) 18 (14.9) 4800 Sinc3 21.4 (18.4) 21.2 (18.3) 21.1 (18.3) 21 (18) 20.5 (17.6) 19.8 (16.8) 19.1 (16.3) 18.2 (15.1) 4800 Sinc4 21.5 (18.6) 21.3 (18.4) 21.2 (18.2) 21.1 (18.1) 20.6 (17.7) 19.9 (17) 19.2 (16.3) 18.2 (15.3) 7200 Sinc1 20.9 (17.8) 20.7 (17.7) 20.6 (17.4) 20.4 (17.5) 20 (17) 19.3 (16.4) 18.6 (15.7) 17.7 (14.7) 7200 Sinc2 21 (18.1) 20.8 (17.9) 20.7 (17.9) 20.6 (17.6) 20.2 (17.2) 19.4 (16.4) 18.7 (15.9) 17.8 (14.9) 7200 Sinc3 21.1 (18.1) 20.9 (18.1) 20.8 (17.9) 20.6 (17.8) 20.2 (17.2) 19.5 (16.5) 18.8 (15.9) 17.9 (14.9) 7200 Sinc4 21.2 (18.1) 21 (18) 20.9 (18.1) 20.7 (18) 20.3 (17.2) 19.6 (16.7) 18.9 (15.9) 18 (15) 14400 Sinc5 20.5 (17.7) 20.3 (17.5) 20.2 (17.3) 20.1 (17.1) 19.8 (16.9) 19.1 (16.1) 18.4 (15.4) 17.5 (14.5) 19200 Sinc5 19.7 (16.8) 19.5 (16.5) 19.4 (16.5) 19.4 (16.3) 19.2 (16.2) 18.8 (15.9) 18 (15.1) 17 (14.2) 25600 Sinc5 18.2 (15.2) 18 (14.9) 18 (15.2) 17.9 (14.7) 17.9 (15.1) 17.8 (14.8) 17 (14.2) 16 (13.2) 40000 Sinc5 17.4 (14.6) 17.2 (14.2) 17.2 (14.2) 17.2 (14.3) 17.2 (14.2) 17.1 (14.3) 16.3 (13.4) 15.3 (12.5) Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 25 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9 Detailed Description 9.1 Overview The ADS1260 and ADS1261 are 5-channel and 10-channel, precision 24-bit, delta-sigma (ΔΣ) ADCs with an integrated analog front end (AFE) and voltage reference. The low-noise and low-drift architecture make the ADCs suitable for precision measurement of low signal level sensors, such as strain-gauge bridges, pressure transducers and temperature sensors. Key features of the ADC are: • Very low noise, 1-GΩ input impedance PGA • High-precision, 24-bit ΔΣ ADC • Internal oscillator • 2.5-V voltage reference • Signal and voltage reference monitors • Excitation current sources • Input level-shift voltage • Sensor burn-out current sources • Temperature sensor • Cyclic redundancy check (CRC) communication error detection • Two voltage reference inputs ( ADS1261) • Four GPIO with AC-excitation ( ADS1261) The analog inputs (AINx) connect to the input multiplexer (MUX). The ADC supports three (five) differential or five (ten) single-ended input configurations for the ADS1260 and ADS1261, respectively. The programmable gain amplifier (PGA) follows the input multiplexer. The PGA is suitable for direct connection to low-level sensors. The gain is programmable from 1 to 128. The PGA bypass option connects the analog inputs directly to the precharge buffered modulator, extending the input voltage range to the power supplies. The PGA output connects to pins CAPP and CAPN. The ADC antialias filter is provided at the PGA output with an external capacitor. The PGA is monitored to verify linear operation. Alarm bits in the status register set if the linear range of the PGA is exceeded. A delta-sigma modulator measures the input voltage relative to the reference voltage to produce the 24-bit conversion result. The differential input range of the ADC is ±VREF / Gain. The digital filter averages and decimates the modulator output data to yield the final, down-sampled conversion result. The sinc filter is programmable (sinc1 through sinc5) allowing optimization of conversion time, conversion noise and line-cycle rejection. The finite impulse response (FIR) filter mode provides single-cycle settled data with simultaneous rejection of 50-Hz and 60-Hz at data rates of 20 SPS or less. The ADC reference is either 2.5-V internal, external or the 5-V analog power supply. The REFOUT pin provides the buffered reference voltage output. The external reference is monitored for low or missing voltage. The ADS1261 provides two voltage reference inputs, multiplexed with the analog inputs. The ADC includes two current sources that provide excitation to resistive sensors (RTD). Additionally, the ADS1261 provides four GPIO control lines. The GPIOs are used for input and output of general-purpose logic signals, as well as providing drive signals for AC-excited bridges. The GPIOs are multiplexed to the analog inputs. The temperature sensor and the power supply voltages are read through the multiplexer. The programmable burn-out test currents connect to the multiplexer output. The currents detect failed sensors or faults in the sensor connection. The level-shift voltage on AINCOM provides the bias for floating sensors. The SPI-compatible serial interface is used to read the conversion data and also to configure and control the ADC. Data communication errors are detected by CRC. The serial interface consists of four signals: CS, SCLK, DIN and DOUT/DRDY. The dual function DOUT/DRDY provides data output and also the data ready signal. The ADC serial interface can be implemented with as little as three pins by tying CS low. 26 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Overview (continued) The ADC clock is either internal or external. The ADC detects the external clock automatically. The nominal clock frequency is 7.3728 MHz (10.24 MHz for 40-kSPS operation). ADC conversions are controlled by the START pin or by the START command. The ADC is programmable for continuous or one-shot conversions. The DRDY or DOUT/DRDY pin provides the conversion data ready signal. When taken low, the RESET pin resets the ADC. The ADC is powered down by the PWDN pin or is powered down in software mode. The ADC operates in either bipolar analog supply configuration (±2.5 V), or in a single 5-V supply configuration. The digital power supply range is 2.7 V to 5 V. The BYPASS pin is the internal subregulator output used for the ADC digital core. 9.2 Functional Block Diagram AVDD AVSS CAPP 2.5-V Ref CAPN 2-V Digital Core LDO Ref Mux REFOUT DVDD BYPASS I/O Voltage Level Shift AVDD AIN0 AIN1 START Ref Monitor Excitation Current Sources Control RESET PWDN Buf DRDY AIN2 AIN3 Input Mux AIN4 AINCOM ADS1261 AC Exc Sensor Burn-out Currents GPIO Mux Temp Sensor AIN5 AIN6 AIN7 AIN8 PGA 24-bit û ADC Digital Filter Serial Interface + CRC Verification PGA Monitor Power Supply Internal Oscillator Clock Mux CS SCLK DOUT/DRDY DIN CLKIN AIN9 DGND Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 27 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.3 Feature Description The following sections describe the functional blocks of the ADC. 9.3.1 Analog Inputs Figure 48 shows the analog input circuit consist of ESD-protection diodes, the input multiplexer and sensor burnout current sources. The ADS1260 has six analog inputs to support five single-ended measurement channels. The ADS1261 has 11 analog inputs to support 10 single-ended measurement channels. Both devices have four internal (system) measurements, and an option where no inputs are connected. ESD Diodes Positive Input Multiplexer MUXP[3:0] bits 7:4 of INPMUX (register address = 11h) AVDD AINCOM 0000 AIN0 0001 AIN1 0010 AIN2 0011 ADS1261 AIN3 0100 AIN4 0101 AIN5 0110 Negative Input Multiplexer MUXN[3:0] bits 3:0 of INPMUX (register address = 11h) MUXP-OUT 0111 AIN6 MUXN-OUT 1000 AIN7 Sensor Burn-out Currents + PGA - 1001 1010 AIN8 AIN9 Temperature Sensor (AVDD ± AVSS) / 4 DVDD / 4 All Open AVSS VCOM: (AVDD + AVSS) / 2 1011 1100 1101 1110 1111 ESD Diodes Figure 48. Analog Input Block Diagram 9.3.1.1 ESD Diodes ESD diodes are incorporated to protect the ADC inputs from possible ESD events occurring during the manufacturing process and during PCB assembly when manufactured in an ESD-controlled environment. For system-level ESD protection, consider the use of external ESD protection devices for pins that are exposed to ESD, including the analog inputs. If either input is driven below AVSS – 0.3 V, or above AVDD + 0.3 V, the internal protection diodes may conduct. If these conditions are possible, use external clamp diodes, series resistors, or both to limit the input current to the specified maximum value. 9.3.1.2 Input Multiplexer The input multiplexer selects the signal for measurement. The multiplexer consists of independent positive and negative sections. See Figure 48 for multiplexer register settings. The multiplexers select any input as positive and any input as negative for the PGA. Because the level-shift voltage connects to AINCOM (only), AINCOM is suitable as the common input for single-ended signals that require a level-shift voltage. The switching sequence of the multiplexer is break-before-make in order to reduce charge injection into the next measurement channel. Be aware that over-driving unused channels beyond the power supplies can effect conversions taking place on active channels. See the Input Overload section for more information. 28 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Feature Description (continued) 9.3.1.3 Temperature Sensor The ADC has an internal temperature sensor. The temperature sensor is comprised of two internal diodes with one diode having 80 times the current density of the other. The difference in current density of the diodes yields a differential output voltage that is proportional to absolute temperature. The temperature sensor reading is converted by the ADC. See Figure 48 for register settings to select the temperature sensor for measurement. Equation 2 shows how to convert the temperature sensor reading to degrees Celsius (˚C): Temperature (°C) = [(Temperature Reading (µV) – 122,400) / 420 µV/°C] + 25°C (2) Measure the temperature sensor with PGA on, gain = 1, burn-out current sources disabled and AC-excitation mode disabled. As a result of the low package-to-PCB thermal resistance, the internal temperature closely tracks the PCB temperature. Be aware that device self-heating increases the internal temperature relative to the surrounding PCB. 9.3.1.4 Power-Supply Readback Read the power-supply voltage by the appropriate input multiplexer selection. The supply voltages are divided to reduce the voltage levels to within the ADC input range. The analog and digital supply readback levels are scaled by Equation 3 and Equation 4, respectively: Analog supply (V) = (AVDD - AVSS) / 4 Digital supply (V) = DVDD / 4 (3) (4) Measure the power supply voltages with either the internal or an external reference. If using an external reference, the minimum reference voltage is 1.5 V. Perform the measurement with PGA enabled, gain = 1, burnout current sources disabled and AC-excitation mode disabled. See Figure 48 for register settings to measure the supply voltages. 9.3.1.5 Inputs Open This configuration opens all inputs. Use this configuration to test the functionality of the sensor burn-out current sources, and the PGA output monitors. When the inputs are open, the current sources drive the PGA inputs to full scale, resulting in an PGA monitor alarm and clipped conversion data. See Figure 48 for register settings to open all inputs. 9.3.1.6 Internal VCOM Connection For this multiplexer configuration, all inputs are open and the PGA inputs are connected to an internal VCOM voltage as defined: (AVDD + AVSS) / 2. Use this mode to measure the ADC noise performance and offset voltage, or to short the inputs for offset calibration. See Figure 48 for register settings of the internal VCOM connection. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 29 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Feature Description (continued) 9.3.1.7 Alternate Functions The ADC has several alternate functions that are multiplexed with the analog inputs. The alternate functions are reference input, current source output, GPIO, AC-excitation and level-shift voltage output. The functions are enabled by programming of the associated registers. The analog inputs retain measurement ability if the alternate functions are programmed. Table 3 summarizes the alternate functions. Table 3. Analog Input Alternate Functions ANALOG INPUTS (1) REFERENCE INPUTS CURRENT SOURCES GPIO/AC-EXCITATION (1) LEVEL-SHIFT VOLTAGE AINCOM — Yes — Yes AIN0 REFP0 Yes — — AIN1 AIN1 REFN0 Yes — — AIN2 AIN2 REFP1 (1) Yes GPIO0/ACX1 — AIN3 AIN3 REFN1 (1) Yes GPIO1/ACX2 — AIN4 AIN4 — Yes GPIO2/ACX1 — — AIN5 — Yes GPIO3/ACX2 — — AIN6 — Yes — — — AIN7 — Yes — — — AIN8 — Yes — — — AIN9 — Yes — — ADS1260 ADS1261 AINCOM AIN0 ADS1261 and ADS1261B only. 9.3.2 PGA The PGA is a low-noise, CMOS differential-input, differential-output amplifier. The PGA extends the dynamic range of the ADC, important when used with low level sensors. The PGA provides gains of 1 through 32 and the ADC provides additional gains of 2 and 4. The combined gains are 1 through 128. Gain is controlled by the GAIN[2:0] register bits as shown in Figure 49. In PGA bypass mode, the input voltage range extends to the analog supplies. The PGA is powered down in bypass mode. BYPASS bit 7 of PGA (register address = 10h) 0: PGA active (shown) 1: PGA bypass 280 Ÿ 350 Ÿ VAINP 8 pF GAIN[2:0] bits 2:0 of PGA (register address = 10h) 000: 1 001: 2 010: 4 011: 8 100: 16 101: 32 110: 64 111:128 VAINN + A1 ± CAPP 12 pF PGA Output Monitors 12 pF 4.7 nF C0G ADC 12 pF ± A2 + 350 Ÿ CAPN 280 Ÿ 8 pF Figure 49. PGA Block Diagram 30 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 The PGA consists of two chopper-stabilized amplifiers (A1 and A2), and a resistor network that determines the PGA gain. The resistor network is precision matched, providing low drift performance. The PGA integrates noise filters to reduce sensitivity to electromagnetic-interference (EMI). The PGA output is monitored to indicate when the operating headroom is exceeded. Pins CAPP and CAPN are the PGA positive and negative outputs, respectively. Connect an external 4.7-nF capacitor (type C0G) as shown in Figure 49. The capacitor filters the modulator sample pulses and with the internal resistors, forms the antialias filter. Place the capacitor as close as possible to the pins using short traces. Avoid running clock traces or other digital traces close to these pins. The full-scale differential input voltage range of the ADC is determined by the reference voltage and gain. Table 4 shows the differential input voltage range verses gain for VREF = 2.5 V. Table 4. Full-Scale Voltage Range (1) GAIN[2:0] BITS GAIN FULL-SCALE DIFFERENTIAL INPUT RANGE (1) 000 1 ±2.500 V 001 2 ±1.250 V 010 4 ±0.625 V 011 8 ±0.312 V 100 16 ±0.156 V 101 32 ±0.078 V 110 64 ±0.039 V 111 128 ±0.0195 V VREF = 2.5 V. Full scale differential input voltage range is proportional to VREF. As with many amplifiers, the PGA has an input voltage range limitation that must not be exceeded in order to maintain linear operation. The specified input voltage range is expressed as the absolute voltage at the positive and negative inputs. As specified in Equation 5, the specified absolute input voltage depends on gain, the expected maximum differential voltage, and the minimum analog power-supply voltage. AVSS + 0.3 V + VIN · (Gain – 1) / 2 · < VAINP and VAINN < AVDD – 0.3 V – VIN · (Gain – 1) / 2 where • • • • • VAINP, VAINN = absolute input voltage VIN = maximum differential input voltage = VAINP - VAINN Gain (for gains = 64 and 128, use gain = 32 in the calculation) AVDD = minimum AVDD voltage AVSS = maximum AVSS voltage Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 (5) Submit Documentation Feedback 31 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com The relationship of the PGA input to the PGA output is shown graphically in Figure 50. The PGA output voltages (VOUTP, VOUTN) depend on the respective absolute input voltage, the differential input voltage, and the PGA gain. To maintain the PGA within the linear operating range, the PGA output voltages must not exceed either AVDD – 0.3 V or AVSS + 0.3 V. The diagram depicts a positive differential input voltage that results in a positive differential output voltage. PGA Input PGA Output AVDD AVDD ± 0.3 V VOUTP = VAINP + VIN Â (Gain ± 1) / 2 VAINP VIN = VAINP Â 9AINN VAINN VOUTN = VAINN ± VIN Â (Gain ± 1) / 2 AVSS + 0.3 V AVSS Figure 50. PGA Input/Output Range 9.3.2.1 PGA Bypass Mode Bypass the PGA to extend the input voltage range up to the analog power supply voltages. In bypass mode, the PGA is bypassed and the analog inputs are connected directly to the precharge buffers of the modulator, thereby extending the input voltage range. Be aware of the increased analog input current in bypass mode. See the Recommended Operating Conditions for the bypass-mode input voltage range specification, and see the Electrical Characteristics for the input current specification. 9.3.2.2 PGA Voltage Monitor The PGA has voltage monitors to provide indication when the PGA is overloaded. In overload condition, the conversion data are no longer valid. If either the PGA positive or negative output exceeds AVDD – 0.2 V, the high alarm bit is set (PGAH_ALM). Similarly, if either PGA positive or negative output is less than AVSS + 0.2 V, the low alarm bit is set (PGAL_ALM). The monitor alarm state is read in the STATUS byte. The monitor alarm is read-only and automatically resets at the start of the next conversion cycle after the overload condition is cleared. The monitor diagram and threshold values are shown in Figure 51 and Figure 52. AVDD ± 0.2 V PGAH_ALM Condition ± + P PGA STATUS Byte + 7 N 6 5 4 3 ± + AVDD AVDD t 0.2 V PGAH_ALM ± 2 1 0 PGA Output P or N P or N AVSS + 0.2 V AVSS PGAL_ALM ± AVSS + 0.2 V + PGAL_ALM Condition Figure 51. PGA Monitor Diagram Figure 52. PGA Monitor Thresholds The PGA monitors consist of fast-responding voltage comparators. Comparator operation is disabled during multiplexer changes to minimize the false triggering during these input switching events. However, it is possible the monitors can detect other transient overload conditions that may occur after gain changes, sensor connection changes, and so on. 32 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.3.3 Reference Voltage The ADC requires a reference voltage for operation. The reference voltage options are 2.5-V internal, one or two external inputs (ADS1260 or ADS1261, respectively) or the 5-V analog power supply. The reference voltage is selected by independent positive and negative reference multiplexers for the reference positive and reference negative voltages, respectively. The default reference is the 5-V analog power supply (AVDD – AVSS). Figure 53 shows the block diagram of the reference multiplexer. Internal Ref AVDD REFOUT 00 01 10 (2) 11 AIN0 (1) 2.5 V AIN2 REFENB bit 4 of REF (register address = 06h) 0: Internal Ref off 1: Internal Ref on (default) RMUXP[1:0] bits 3:2 of REF (register address = 06h) VREFP 10 PF BUF 00 01 10 (2) 11 AVSS AIN1 AIN3 ADC VREFN RMUXN[1:0] bits 1:0 of REF (register address = 06h) (1) The internal reference requires a 10-µF capacitor connected to pins REFOUT and AVSS. (2) ADS1261 only. Figure 53. Reference Input Diagram Program the RMUXP[1:0] and RMUXN[1:0] bits of the REF register to select the positive and negative reference voltages, respectively. The positive reference selections are internal positive, AIN0, AIN2, or AVDD. The negative reference input selections are internal negative, AIN1, AIN3, or AVSS. The reference low-voltage monitor is located after the reference multiplexer. See the Reference Monitor section for more information. 9.3.3.1 Internal Reference The ADC incorporates a 2.5-V reference that is enabled by the REFENB bit of the REF register (default = off). Program the reference multiplexer bits RMUXP[1:0] and RMUXN[1:0] to 00b to select the internal reference. A 10-μF capacitor is required between pins REFOUT and AVSS to filter reference noise. REFOUT is the reference output and AVSS is the reference return. Use a star-layout connection or plane connection for the reference return, connecting close to the AVSS pin. When the reference is enabled, be aware of the settling time before beginning conversions. Also be aware of the reference inrush current that may result in a transient droop of the AVDD voltage. Enable the internal reference for sensor excitation current source operation. 9.3.3.2 External Reference Use an external reference by applying the reference voltage to the designated analog inputs. The reference inputs are differential with positive and negative inputs. Program the reference multiplexer bits RMUXP[1:0] and RMUXN[1:0] to 10b or 11b to select inputs AIN0/AIN1 or AIN2/AIN3, respectively (AIN2/AIN3 is available only for the ADS1261). For application that use multiple references, it is possible to connect the reference grounds together and use a single input pin for ground. Follow the specified absolute and differential reference voltage operating conditions, as specified in the Recommended Operating Conditions. Connect a 100-nF capacitor across the reference input pins to filter noise. Be aware of the reference input current if reference impedances are present. Consider the error to the overall system accuracy. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 33 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.3.3.3 AVDD - AVSS Reference (Default) A third reference option is the 5-V analog power supply (AVDD - AVSS). Select this reference option by setting the reference multiplexer bits RMUXP[1:0] and RMUXN[1:0] to 01b. For a 6-wire load cell application that uses excitation sense lines, or for AC-excitation operation, connect the excitation sense lines to the analog input reference inputs and program the ADC for external reference operation. 9.3.3.4 Reference Monitor The ADC incorporates a reference monitor that detects an invalid reference voltage. As shown in Figure 54 and Figure 55, if the reference voltage (VREF = VREFP – VREFN) is below 0.4 V, the REFL_ALM bit is set in the STATUS byte. The alarm is read-only and resets at the next conversion after the low reference condition is cleared. Use the reference monitor to detect a missing or failed reference voltage. To implement detection of a missing reference, use a 100-kΩ resistor across the reference inputs. If either input is unconnected, the resistor biases the differential reference input towards 0 V so that the missing reference can be detected. STATUS Byte 6 7 + External Reference _ 5 100 k AIN1 3 4 2 1 0 x AIN0 Ref MUX Differential Reference Voltage 0.4 V, Typical REFL_ALM + _ _ 0.4 V + Reference Low Condition Figure 54. Reference Monitor Figure 55. Reference Monitor Threshold 9.3.4 Level-Shift Voltage (VBIAS) The ADC integrates a level-shift voltage that can be connected to the AINCOM pin by an internal switch. As shown in Figure 56, the level-shift voltage is the mid-voltage between AVDD and AVSS. The purpose of the voltage is to shift the signal level of floating sensors to within the input range of the ADC. Isolated thermocouples and piezoelectric sensors are examples of sensors that are suitable for connection to the level-shift voltage. For these sensors, connect the negative lead to the AINCOM pin and enable the level-shift voltage. AINCOM 100 Ÿ V = (AVDD + AVSS) / 2 VBIAS bit 4 of INPBIAS (register address = 12h) 0: off (default) 1: on Figure 56. Level-Shift Voltage Diagram The turn-on time of the level-shift voltage depends on the total external capacitance connected from the AINCOM pin to ground or AVSS. Table 5 lists the level-shift voltage settling times for various load capacitance. Be certain the level-shift voltage is fully settled before starting a conversion. Table 5. Level-Shift Enable Time 34 LOAD CAPACITANCE LEVEL-SHIFT VOLTAGE SETTLING TIME 0.1 µF 0.22 ms 1 µF 2.2 ms 10 µF 22 ms Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.3.5 Burn-Out Current Sources The burn-out current sources are used to detect the occurrence of sensor burn-out or break. If the sensor or sensor connection is open, the currents drive either or both positive and negative PGA inputs to opposite supply voltages where the occurrence of an open sensor is detected by the PGA monitors or detected by the host for out-of-range (or clipped) conversion data. Figure 57 shows the burn-out currents connect at the output of the analog input multiplexer. The currents sink and source, and are configurable in pullup or pulldown mode. In pullup mode, the sourcing current connects to the positive input channel and the sinking current connects to the negative input channel. In this configuration, an open circuit pulls the inputs to positive full scale. The currents are Off, 0.050 µA, 0.2 µA, 1 µA, and 10 µA. See the Burn-out Current Source section for application information. AVDD BOCS[2:0] bits 2:0 of INPBIAS (register address = 12h) 000: off 001: 0.05 uA 010: 0.2 uA 011: 1 uA 100: 10 uA MUXP AIN0 AINP PGA AINN AINCOM BOCSP bit 3 of INPBIAS (register address = 12h) MUXN 0 = Pull-up mode (shown) 1 = Pull-down Mode AVSS Figure 57. Burn-Out Current Sources Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 35 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.3.6 Sensor-Excitation Current Sources (IDAC1 and IDAC2) The ADC incorporates two current sources that are used to provide excitation current to a resistive temperature device (RTD), thermistor, diode and other sensor type that require constant current biasing. The currents are programmable over the 50 μA to 3000 μA range and are internally multiplexed to all analog input pins. The current source multiplexer is shown in Figure 58. The IMUX1 and IMUX2 register bits connect the corresponding current source to the analog inputs. The IMAG1 and IMAG2 register bits program the corresponding current magnitude. Enable the internal reference for current source operation. The current source value can be doubled or an intermediate value produced by connecting the current sources to the same analog input. Take care not to exceed the current source compliance voltage range. That is, when the current source is loaded by resistance, the voltage at the pin increases and must not exceed specification; otherwise the specified current source accuracy is not met. IDAC1 IMUX1[3:0] bits 3:0 of IMUX (register address = 0Dh) IDAC2 IMUX2[3:0] bits 7:4 of IMUX (register address = 0Dh) 0000 AIN0 AIN1 IDAC1 IMAG1[3:0] bits 3:0 of IMAG (register address = 0Eh) 0010 AIN2 0011 AIN3 0100 AIN4 0101 AIN5 0110 AIN6 ADS1261 AVDD 0001 0111 AIN7 1000 AIN8 1001 AIN9 AVDD IDAC2 IMAG2[3:0] bits 7:4 of IMAG (register address = 0Eh) 0000: off 0001: 50 µA 0010: 100 µA 0011: 250 µA 0100: 500 µA 0101: 750 µA 0110: 1000 µA 0111: 1500 µA 1000: 2000 µA 1001: 2500 µA 1010: 3000 µA 1010 AINCOM Open 1111 Figure 58. Current Source Connection 36 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.3.7 General-Purpose Input/Outputs (GPIOs) The ADS1261 and ADS1261B devices provide four GPIO pins, GPIO0 through GPIO3. The GPIOs are digital inputs/outputs that are referenced to analog AVDD and AVSS. The GPIOs are read and written by the GPIO_DAT bits of register MODE3. The GPIOs are multiplexed with analog inputs AIN2 to AIN5. As shown in Figure 59, the GPIOs have a series of programming registers. Bits GPIO_CON[3:0] connect the GPIOs to the associated pin (1 = connect). Bits GPIO_DIR program the direction of the GPIOs; (0 = output, 1 = input). The input voltage threshold is the voltage value between AVDD and AVSS. Bits GPIO_DAT[3:0] are the data values for the GPIOs. Observe that if a GPIO pin is programmed as an output, the value read is the value previously written to the register data, not the actual state of the pin. The GPIOs also provide the AC-excitation drive signals. AC-excitation mode override the GPIO register data values. See the AC-Excitation Mode section for details. AVDD Write AC-Excitation Mode CHOP[1:0] bits 6:5 of MODE1 (register address = 03h) GPIO_CON[3:0] bits 7:4 of MODE2 (register address = 04h) Write 0: GPIO not connected (default) 1: GPIO connected GPIO_DAT[3:0] bits 3:0 of MODE3 (register address = 05h) 00: Normal mode (default) 01: Chop mode 10: 2-wire AC-excitation mode 11: 4-wire AC-excitation mode 0: VGPIO low (default) 1: VGPIO high GPIO0 0 GPIO1 1 AIN2 Read AIN3 GPIO2 + AIN4 MUX Read Select GPIO3 AIN5 ± GPIO_DIR[3:0] bits 3:0 of MODE2 (register address = 04h) 0: GPIO is output (default) 1: GPIO is input AVDD + AVSS 2 AVSS Figure 59. GPIO Block Diagram 9.3.8 Oversampling The ADC operates on the principle of oversampling, defined as the ratio of the sample rate of the modulator to that of the ADC output data rate. Oversampling improves ADC noise by digital bandwidth limiting (low-pass filtering) of the data. The digital filter also performs data rate reduction (decimation) in order to reduce the data rate proportional with the amount of data filtering. 9.3.9 Modulator The modulator is an inherently stable, fourth-order, 2 + 2 pipelined ΔΣ modulator. The modulator samples the analog input voltage at a high sample rate (fMOD = fCLK / 8) and converts the analog input to a ones-density bitstream given by the ratio of the input signal to the reference voltage. The modulator shapes the noise of the converter to high frequency, where the noise is removed by the digital filter. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 37 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.3.10 Digital Filter The digital filter receives the modulator output data and produces a high-resolution conversion result. The digital filter low-pass filters and decimates the modulator data (data rate reduction), yielding the final data output. By adjusting the type of filtering, tradeoffs are made between resolution, data throughput and line cycle rejection. The digital filter has two selectable modes: sin (x) / x (sinc) mode and finite impulse response (FIR) mode (see Figure 60). The sinc mode provides data rates of 2.5 SPS through 40000 SPS with variable sinc orders of 1 through 5. The FIR filter provides simultaneous rejection of 50-Hz and 60-Hz frequencies with data rates 2.5 SPS through 20 SPS while providing single-cycle settled conversions. Sinc Filter Section 40000 SPS to 14400 SPS fCLK / 8 Sinc5 Filter Modulator 7200 SPS to 2.5 SPS SincN Filter Filter Mux FIR Filter Section To Offset/Gain Calibration 20 SPS ( = Data rate reduction) FIR Averager 10 SPS 5 SPS 2.5 SPS Figure 60. Digital Filter Block Diagram 9.3.10.1 Sinc Filter The sinc filter is composed of two stages: a variable-decimation sinc5 filter, followed by a variable-decimation, variable-order sinc filter. The first stage filters and down-samples the modulator data to yield data rates of 40000 SPS, 25600 SPS, 19200 SPS, and 14400 SPS. These data rates bypass the second stage and as a result have a sinc5 characteristic filter response. The second stage receives data from the first stage at a fixed rate of 14400 SPS. The data rate is reduced to the range 7200 SPS to 2.5 SPS, with programmable orders of sinc. The data rate is programmed by the DR[4:0] bits of register MODE0. The filter mode is programmed by the FILTER[2:0] bits of register MODE0 (see Table 32). 9.3.10.1.1 Sinc Filter Frequency Response The characteristic of the sinc filter is low pass. The filter reduces noise present in the signal and noise present within the ADC. Changing the data rate and filter order changes the filter bandwidth. 0 0 -20 -20 -40 -40 Amplitude (dB) Amplitude (dB) As shown in Figure 61 and Figure 62, the first-stage sinc5 filter has frequency response nulls occurring at N · fDATA, where N = 1, 2, 3 and so on. At the null frequencies, the filter has zero gain. Data rates of 25600 SPS and 19200 SPS have similar frequency response. -60 -80 -100 -80 -100 -120 -120 -140 -140 -160 -160 0 10 20 30 40 50 60 70 80 Frequency (kHz) 90 100 110 120 Submit Documentation Feedback 0 10 20 D201 Figure 61. Frequency Response (40000 SPS) 38 -60 30 40 50 60 70 80 Frequency (kHz) 90 100 110 120 D002 Figure 62. Frequency Response (14400 SPS) Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 The second stage superimposes frequency response nulls to the nulls of the first stage 14400 SPS output. The first of the superimposed response nulls occurs at the data rate, followed by nulls occurring at multiples of the data rate. Figure 63 illustrates the frequency response for various orders of sinc at data rate of 2400 SPS. This data rate has five nulls between the larger nulls at multiples of 14400 Hz. This frequency response is similar to that of data rates 2.5 SPS to 7200 SPS. Figure 64 shows the frequency response nulls for 10 SPS. 0 0 sinc1 sinc2 sinc3 sinc4 -20 -40 Amplitude (dB) Amplitude (dB) -40 sinc1 sinc2 sinc3 sinc4 -20 -60 -80 -100 -60 -80 -100 -120 -120 -140 -140 -160 -160 0 5 10 15 20 25 30 Frequency (kHz) 35 40 45 0 10 20 30 40 D003 Figure 63. Sinc Frequency Response (2400 SPS) 50 60 70 80 Frequency (Hz) 90 100 110 120 D004 Figure 64. Sinc Frequency Response (10 SPS) Figure 65 and Figure 66 show the frequency response of data rates 50 SPS and 60 SPS, respectively. Increase the attenuation at 50 Hz or 60 Hz and harmonics by increasing the order of the sinc filter, as shown in the figures. 0 0 sinc1 sinc2 sinc3 sinc4 -20 -40 Amplitude (dB) Amplitude (dB) -40 sinc1 sinc2 sinc3 sinc4 -20 -60 -80 -100 -60 -80 -100 -120 -120 -140 -140 -160 -160 0 50 100 150 200 250 300 350 400 450 500 550 600 Frequency (Hz) D005 0 Figure 65. Sinc Frequency Response (50 SPS) 60 120 180 240 300 360 Frequency (Hz) 420 480 540 600 D006 Figure 66. Sinc Frequency Response (60 SPS) Figure 67 and Figure 68 show the detailed frequency response at 50 SPS and 60 SPS, respectively. 0 0 sinc1 sinc2 sinc3 sinc4 -20 -40 Ampliude (dB) Amplitude (dB) -40 -60 -80 -100 -60 -80 -100 -120 -120 -140 -140 -160 45 46 47 48 49 50 51 Frequency (Hz) 52 53 54 sinc1 sinc2 sinc3 sinc4 -20 55 -160 55 56 D009 Figure 67. Detail Sinc Frequency Response (50 SPS) 57 58 59 60 61 Frequency (Hz) 62 63 64 65 D010 Figure 68. Detail Sinc Frequency Response (60 SPS) Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 39 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.3.10.2 FIR Filter The finite impulse response (FIR) filter is a coefficient based filter architecture that provides an overall low-pass filter response. The filter provides simultaneous attenuation of 50 Hz and 60 Hz and harmonics at data rates of 20 SPS to 2.5 SPS. The conversion latency time of the FIR filter data rates are single-cycle. As shown in Figure 60, the FIR filter receives pre-filtered data from the sinc filter. The FIR filter decimates the data to yield the output data rates of 20 SPS. A variable averager (sinc1) provides data rates of 10 SPS, 5 SPS, and 2.5 SPS. Table 6 lists the bandwidth of the data rates in FIR filter mode. 9.3.10.2.1 FIR Filter Frequency Response 0 0 -20 -20 -40 -40 Amplitude (dB) Amplitude (dB) Figure 69 and Figure 70 show the FIR filter frequency attenuates 50 Hz and 60 Hz by a series of response nulls placed close to these frequencies. The response nulls are repeated at harmonics of 50 Hz and 60 Hz. -60 -80 -100 -60 -80 -100 -120 -120 -140 -140 -160 40 -160 0 30 60 90 120 150 180 Frequency (Hz) 210 240 270 300 45 50 D011 55 60 Frequency (Hz) 65 70 D012 Figure 70. FIR Frequency Response Detail (20 SPS) Figure 69. FIR Frequency Response (20 SPS) Figure 71 is the FIR filter response at 10 SPS. As a result of the variable averager, new frequency nulls are superimposed. The first null appears at the date rate. Additional nulls occur at frequencies folded around multiples of 20 Hz. 0 -20 Amplitude (dB) -40 -60 -80 -100 -120 -140 -160 0 30 60 90 120 150 180 Frequency (Hz) 210 240 270 300 D013 Figure 71. FIR Frequency Response (10 SPS) 40 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.3.10.3 Filter Bandwidth The bandwidth of the filter depends on the data rate and the filter mode. Be aware that the bandwidth of the entire system is the combined response of the filter, the antialias filter and external filters. Table 6 lists the bandwidth versus data rate and filter mode. Table 6 also lists the filter modes available for each data rate. Table 6. Filter Bandwidth -3-dB BANDWIDTH (Hz) DATA RATE (SPS) FIR SINC1 SINC2 SINC3 SINC4 SINC5 2.5 1.2 1.10 0.80 0.65 0.58 — 5 2.4 2.23 1.60 1.33 1.15 — 10 4.7 4.43 3.20 2.62 2.28 — 16.6 — 7.38 5.33 4.37 3.80 — 20 13 8.85 6.38 5.25 4.63 — 50 — 22.1 16.0 13.1 11.4 — 60 — 26.6 19.1 15.7 13.7 — 100 — 44.3 31.9 26.2 22.8 — 400 — 177 128 105 91.0 — 1200 — 525 381 314 273 — 2400 — 1015 751 623 544 — 4800 — 1798 1421 1214 1077 — 7200 — 2310 1972 1750 1590 — 14400 — — — — — 2940 19200 — — — — — 3920 25600 — — — — — 5227 40000 — — — — — 8167 Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 41 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.3.10.4 50-Hz and 60-Hz Normal Mode Rejection To reduce 50-Hz and 60-Hz noise interference, configure the conversion period to reject the noise at 50 Hz and 60 Hz. 50-Hz and 60-Hz noise rejection depends on the filter type. Table 7 summarizes the 50-Hz and 60-Hz noise rejection versus data rate and filter type. The table values are based on 2% and 6% tolerance of noise frequency to ADC clock frequency. For the sinc filter mode, noise rejection is increased by increasing the order of the filter. Common mode noise is also rejected at these frequencies. Table 7. 50-Hz and 60-Hz Normal Mode Rejection DIGITAL FILTER RESPONSE (dB) DATA RATE (SPS) FILTER TYPE 50 Hz ±2% 60 Hz ±2% 50 Hz ±6% 60 Hz ±6% 2.5 FIR –113 –99 –88 –80 2.5 Sinc1 –36 –37 –40 –37 2.5 Sinc2 –72 –74 –80 –74 2.5 Sinc3 –108 –111 –120 –111 2.5 Sinc4 –144 –148 –160 –148 5 FIR –111 –95 –77 –76 5 Sinc1 –34 –34 –30 –30 5 Sinc2 –68 –68 –60 –60 5 Sinc3 –102 –102 –90 –90 5 Sinc4 –136 –136 –120 –120 10 FIR –111 –94 –73 –68 10 Sinc1 –34 –34 –25 –25 10 Sinc2 –68 –68 –50 –50 10 Sinc3 –102 –102 –75 –75 10 Sinc4 –136 –136 –100 –100 16.6 Sinc1 –34 –21 –24 –21 16.6 Sinc2 –68 –42 –48 –42 16.6 Sinc3 –102 –63 –72 –63 16.6 Sinc4 –136 –84 –96 –84 20 FIR –95 –94 –66 –66 20 Sinc1 –18 –34 –18 –24 20 Sinc2 –36 –68 –36 –48 20 Sinc3 –54 –102 –54 –72 20 Sinc4 –72 –136 –72 –96 50 Sinc1 –34 –15 –24 –15 50 Sinc2 –68 –30 –48 –30 50 Sinc3 –102 –45 –72 –45 50 Sinc4 –136 –60 –96 –60 60 Sinc1 –13 –34 –12 –24 60 Sinc2 –27 –68 –24 –48 60 Sinc3 –40 –102 –36 –72 60 Sinc4 –53 –136 –48 –96 42 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.4 Device Functional Modes 9.4.1 Conversion Control Conversions are controlled by either the START pin or by the START command. If using commands to control conversions, keep the START pin low to avoid contentions between pin and commands. Commands take affect on the 16th falling SCLK edge (CRC mode disabled) or on the 32nd falling SCLK edge (CRC mode enabled). See Figure 4 for conversion-control timing details. The ADC provides two conversion modes: continuous and pulse. The continuous-conversion mode performs conversions indefinitely until stopped by the user. Pulse-conversion mode performs one conversion and then stops. The conversion mode is programmed by the CONVRT bit (bit 4 of register MODE0). 9.4.1.1 Continuous-Conversion Mode This conversion mode performs continuous conversions until stopped by the user. To start conversions, take the START pin high or send the START command. DRDY is driven high at the time the conversion is initiated. DRDY is driven low when the conversion data are ready. Conversion data are available to read at that time. Conversions are stopped by taking the START pin low or by sending the STOP command. When conversions are stopped, the conversion in progress runs to completion. To restart a conversion that is in progress, toggle the START pin low-then-high or send a new START command. 9.4.1.2 Pulse-Conversion Mode In pulse-conversion mode, the ADC performs one conversion when START is taken high or when the START command is sent. When the conversion completes, further conversions stop. The DRDY output is driven high to indicate the conversion is in progress, and is driven low when the conversion data are ready. Conversion data are available to read at that time. To restart a conversion in progress, toggle the START pin low-then-high or send a new START command. Driving START low or sending the STOP command does not interrupt the current conversion. 9.4.1.3 Conversion Latency The digital filter averages data from the modulator in order to produce the conversion result. The stages of the digital filter must have settled data in order to provide fully-settled output data. The order and the decimation ratio of the digital filter determine the amount of data averaged, and in turn, affect the latency of the conversion data. The FIR and sinc1 filter modes are zero latency because the ADC provides the conversion result in one conversion cycle. Latency time is an important consideration for the data throughput rate in multiplexed applications. Table 8 lists the conversion latency values of the ADC. Conversion latency is defined as the time from the start of the first conversion, by taking the START pin high or sending the START command, to the time when the conversion data are ready. If the input signal is settled, then the ADC provides fully settled data under this condition. The conversion latency values listed in the table are with the start-conversion delay parameter = 50 µs, and include the overhead time needed to process the data. After the first conversion completes (in continuous conversion mode), the period of the following conversions are equal to 1/fDATA. The first conversion latency in chop and AC-excitation modes are twice the values listed in the table. Also when operating in these modes, the period of the following conversions are equal to the values listed in the table. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 43 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Device Functional Modes (continued) Table 8. Conversion Latency (1) CONVERSION LATENCY - t(STDR) (1) (ms) DATA RATE (SPS) FIR SINC1 SINC2 SINC3 SINC4 SINC5 2.5 402.2 400.4 800.4 1,200 1,600 — 5 202.2 200.4 400.4 600.4 800.4 — 10 102.2 100.4 200.4 300.4 400.4 — 16.6 — 60.43 120.4 180.4 240.4 — 20 52.23 50.43 100.4 150.4 200.4 — 50 — 20.43 40.43 60.43 80.43 — 60 — 17.09 33.76 50.43 67.09 — 100 — 10.43 20.43 30.43 40.43 — 400 — 2.925 5.425 7.925 10.43 — 1200 — 1.258 2.091 2.925 3.758 — 2400 — 0.841 1.258 1.675 2.091 — 4800 — 0.633 0.841 1.050 1.258 — 7200 — 0.564 0.702 0.841 0.980 — 14400 — — — — — 0.423 19200 — — — — — 0.336 25600 — — — — — 0.271 40000 — — — — — 0.179 Chop mode off, conversion-start delay = 50 µs (DELAY[3:0] = 0001) If the input signal changes while free-running conversions, the conversion data are a mix of old and new data, as shown in Figure 72. After an input change, the number of conversion periods required for fully settled data are determined by dividing the conversion latency by the period of the data rate, plus add one conversion period to the result. In chop mode and AC-excitation mode, use twice the latency values listed in the table. VIN = VAINP - VAINN Old VIN New VIN Old data Fully settled new data Mix of old data and new data DRDY pin Figure 72. Input Change During Conversions 9.4.1.4 Start-Conversion Delay Some applications may require a delay at the start of a conversion in order to allow settling time for the PGA output antialias filter or to allow time after input and configuration changes. The ADC provides a user programmable delay time that delays the start of a new conversion. The default value is 50 μs. This allows for settling of the antialiasing filter. Use additional delay time as needed to provide settling time for external components. The delay time increases the conversion latency values listed in Table 8. As an alternative to the programmable start-conversion delay, manually delay the start of conversion after input and configuration changes. Start-conversion delay is an important consideration for operation in AC-excitation mode. In this mode, the reference inputs to the bridge, and therefore, the bridge output signals are reversed for each conversion As a result, time delay is required to allow for settling of external filter components after reversal. As a general guideline, set the start-conversion delay parameter to a minimum of 15 times the R-C time constant of the signal input and reference input filters. 44 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.4.2 Chop Mode The PGA and modulator are chopper-stabilized at high frequency in order to reduce offset voltage, offset voltage drift and 1/f noise. The offset and noise artifacts are modulated to high frequency and are removed by the digital filter. Although chopper stabilization is designed to remove all offset, a small offset voltage may remain. The optional global chop mode removes the remaining offset errors, providing exceptional offset voltage drift performance. Chop mode alternates the signal polarity of consecutive conversions. The ADC subtracts consecutive, alternatephase conversions to yield the final conversion data. The result of subtraction removes the offset. CHOP[1:0] bits 6:5 of MODE1 (register address = 03h) 00: Normal mode 01: Chop mode 10: 2-wire AC excitation mode 11: 4-wire AC excitation mode Chop Switch VOFS VAINP Input MUX + PGA VAINN ADC AIN0 ADC Digital Filter Chop Control Offset Cal Full-Scale Cal Conversion Output AINCOM Figure 73. ADC Chop Mode As shown in Figure 73, the internal chop switch reverses the signal after the input multiplexer. VOFS models the internal offset voltage. The operational sequence of chop mode is as follows: Conversion C1: VAINP – VAINN – VOFS → First conversion withheld after start Conversion C2: VAINN – VAINP – VOFS → Output 1 = (C1 – C2) / 2 = VAINP – VAINN Conversion C3: VAINP – VAINN – VOFS → Output 2 = (C3 – C2) / 2 = VAINP – VAINN The sequence repeats for all conversions. Because of the internal mathematical operations, the chop mode data rate is reduced. The chop mode data rate is proportional to the order of the sinc filter. Referring to Table 8, the new data rate is equal to 1 / latency values and the first conversion latency is 2 × latency values. Because of the two-point data averaging arising from the mathematical operations, noise is reduced by √2. For chop mode, divide the noise data values shown in Table 1 by √2 to derive the new noise performance data. The null frequencies of the digital filter are not changed in chop-mode operation. However, new null frequencies appear at multiples of fDATA / 2. 9.4.3 AC-Excitation Mode Resistive bridge sensors are excited by DC or AC voltages; for DC or AC currents. DC voltage excitation is the most common type of excitation. AC excitation reverses the polarity of the voltage by the use of external switching components. Similar in concept to chop mode, the result of the voltage reversal removes offset voltage in the connections leading from the bridge to the ADC inputs. This removal includes the offset voltage of the ADC itself. The ADS1261 and ADS1261B devices provide the signals necessary to drive the external switching components in order to reverse the bridge voltage. The timing of the drive signals is synchronized to the ADC conversion phase. During one conversion phase, the voltage polarity is normal. For the alternate conversion phase, the voltage polarity is reversed. The ADC compensates the reversed polarity conversion by internal reversal of the reference voltage. The ADC subtracts the data corresponding to the normal and reverse phases in order to remove offset voltage from the input. The ADC output drive signals do not overlap in order to avoid bridge cross-conduction that can otherwise occur during excitation voltage reversal. The switch rate of the AC-excitation drive signals are at the data rate to avoid unnecessary fast switching. See Figure 7 for output drive timing. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 45 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Table 9 shows the AC-excitation drive signals and the associated GPIO pins. Program the AC-excitation mode using the CHOP[1:0] bits in register MODE1. AC excitation can be programmed for two-wire or four-wire drive mode. For two-wire operation, two drive signals are provided on the GPIOs. If needed, use two external inverters to derive four signals to drive discrete transistors. The GPIO drive levels are referred to the 5-V analog supply. Be aware that the AC-excitation mode changes the nominal data rate, depending on the order of the sinc filter. See the Chop Mode section for details of the effective data rate. Table 9. AC-Excitation Drive Pins DEVICE PIN GPIO 2-WIRE MODE (CHOP[1:0] = 10) 4-WIRE MODE (CHOP[1:0] = 11) AIN2 GPIO0 ACX1 ACX1 AIN3 GPIO1 ACX2 ACX2 AIN4 GPIO2 — ACX1 AIN5 GPIO3 — ACX2 9.4.4 ADC Clock Mode Operate the ADC with an external clock or with the internal oscillator. The clock frequency is 7.3728 MHz, except for fDATA = 40000 SPS then fCLK = 10.24 MHz (internal or external). For external clock operation, apply the clock signal to CLKIN. For internal-clock operation, connect CLKIN to DGND. The internal oscillator begins operation immediately at power-up. The ADC automatically selects the clock mode of operation. Read the clock mode bit in the STATUS register to determine the clock mode. 9.4.5 Power-Down Mode The ADC has two power-down modes: hardware and software. In both power-down modes, the digital outputs remain driven. The digital inputs must be maintained at VIH or VIL levels (do not float the digital inputs). The internal low-dropout regulator remains on, drawing 25 µA (typical) from DVDD. 9.4.5.1 Hardware Power-Down Take the PWDN pin low to engage hardware power-down mode. Except for the internal LDO, all ADC functions are disabled. To exit hardware power-down mode (wake-up) take the PWDN pin high. The register values are not reset at wake-up. The internal reference is shut down in this mode; therefore, be sure to accommodate the start-up time of the internal reference before starting conversions. 9.4.5.2 Software Power-Down Set the PWDN bit (bit 7 of register MODE3) to engage software power-down mode. Similar to the operation of hardware power-down mode, software mode powers down the internal functions except the serial interface remains powered, and the internal reference bias is unchanged (On or Off). Exit the software power-down mode by clearing the PWDN bit. The register values are not reset. 9.4.6 Reset The ADC is reset in three ways: at power-on, by the RESET pin, and by the RESET command. When reset, the serial interface, conversion-control logic, digital filter, and register values are reset. The RESET bit of the STATUS byte is set to indicate a device reset has occurred by any of the three reset methods. Clear the bit to detect the next device reset. If the START pin is high after reset, the ADC begins conversions. 9.4.6.1 Power-on Reset At power-on, after the supply voltages cross the reset-voltage thresholds, the ADC is reset and 216 fCLK cycles later the ADC is ready for communication. Until this time, DRDY is held low. DRDY is driven high to indicate when the ADC is ready for communication. If the START pin is high, the conversion cycle starts 512 / fCLK cycle after DRDY asserts high. Figure 5 shows the power-on reset behavior. 9.4.6.2 Reset by Pin Reset the ADC by taking the RESET pin low and then returning the pin high. After reset, the conversion starts 512 / fCLK cycles later. See Figure 6 for RESET timing. 46 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.4.6.3 Reset by Command Reset the ADC by the RESET command. Toggle CS high to make sure the serial interface resets before sending the command. For applications that tie CS low, see the Serial Interface Auto-Reset section for information on how to reset the serial interface. After reset, the conversion starts 512 / fCLK cycles later. See Figure 6 for timing details. 9.4.7 Calibration The ADC incorporates calibration registers and associated commands to calibrate offset and full-scale errors. Calibrate by using calibration commands, or calibrate by writing to the calibration registers directly (user calibration). To calibrate by command, send the offset or full-scale calibration commands. To user calibrate, write values to the calibration registers based on calculations of the conversion data. Perform offset calibration before full-scale calibration. 9.4.7.1 Offset and Full-Scale Calibration Use the offset and full-scale (gain) registers to correct offset or full-scale errors, respectively. As shown in Figure 74, the offset calibration register is subtracted from the output data before multiplication by the full-scale register, which is divided by 400000h. After the calibration operation, the final output data are clipped to 24 bits. VAINP + Digital Filter ADC ADC VAINN Output Data Clipped to 24 bits Final Output 1/400000h FSCAL[2:0] registers (register addresses = 0Ah, 0Bh, 0Ch) OFCAL[2:0] registers (register addresses = 07h, 08h, 09h) Figure 74. Calibration Block Diagram Equation 6 shows the internal calibration. Final Output Data = (Filter Output - OFCAL[2:0]) · FSCAL[2:0] / 400000h (6) 9.4.7.1.1 Offset Calibration Registers The offset calibration word is 24 bits, consisting of three 8-bit registers, as listed in Table 10. The offset value is subtracted from the conversion result. The offset value is in two's complement format with a maximum positive value equal to 7FFFFFh, and a maximum negative value equal to 800000h. A register value equal to 000000h has no offset correction. Although the offset calibration register provides a wide range of possible offset values, the input signal after calibration cannot exceed ±106% of the pre-calibrated range; otherwise, the ADC is overranged. Table 11 lists example values of the offset register. Table 10. Offset Calibration Registers REGISTER BYTE ORDER ADDRESS OFCAL0 LSB 07h B7 B6 B5 B4 B3 B2 B1 OFCAL1 MID 08h B15 B14 B13 B12 B11 B10 B9 B8 OFCAL2 MSB 09h B23 (MSB) B22 B21 B20 B19 B18 B17 B16 BIT ORDER B0 (LSB) Table 11. Offset Calibration Register Values (1) OFCAL[2:0] REGISTER VALUE IDEAL OUTPUT VALUE (1) 000001h FFFFFFh 000000h 000000h FFFFFFh 000001h Output value with no offset error Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 47 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.4.7.1.2 Full-Scale Calibration Registers The full-scale calibration word is 24 bits consisting of three 8-bit registers, as listed in Table 12. The full-scale calibration value is in straight-binary format, normalized to a unity-gain factor at a value of 400000h. Table 13 lists register values for selected gain factors. Gain errors greater than unity are corrected by using full-scale values less than 400000h. Although the full-scale register provides a wide range of possible values, the input signal after calibration must not exceed ±106% of the precalibrated input range; otherwise, the ADC is overranged. Table 12. Full-Scale Calibration Registers REGISTER BYTE ORDER ADDRESS FSCAL0 LSB 0Ah B7 B6 B5 B4 B3 B2 B1 FSCAL1 MID 0Bh B15 B14 B13 B12 B11 B10 B9 B8 FSCAL2 MSB 0Ch B23 (MSB) B22 B21 B20 B19 B18 B17 B16 BIT ORDER B0 (LSB) Table 13. Full-Scale Calibration Register Values FSCAL[2:0] REGISTER VALUE GAIN FACTOR 433333h 1.05 400000h 1.00 3CCCCCh 0.95 9.4.7.2 Offset Self-Calibration (SFOCAL) The offset self-calibration command corrects offset errors internal to the ADC. When the offset self-calibration command is sent, the ADC disconnects the external inputs, shorts the inputs to the PGA, and then averages 16 conversion results to compute the calibration value. Averaging the data reduces conversion noise to improve calibration accuracy. When calibration is complete, the ADC restores the user input and performs one conversion using the new calibration value. 9.4.7.3 Offset System-Calibration (SYOCAL) The offset system-calibration command corrects system offset errors. For this type of calibration, the user shorts the inputs to either the ADC or to the system. When the command is sent, the ADC averages 16 conversion results to compute the calibration value. Averaging the data reduces conversion noise to improve calibration accuracy. When calibration is complete, the ADC performs one conversion using the new calibration value. 9.4.7.4 Full-Scale Calibration (GANCAL) The full-scale calibration command corrects gain error. To calibrate, apply a positive full-scale calibration voltage to the ADC, wait for the signal to settle, and then send the calibration command. The ADC averages 16 conversion results to compute the calibration value. Averaging the data reduces conversion noise to improve calibration accuracy. The ADC computes the full-scale calibration value so that the calibration voltage is scaled to positive full scale output code. When calibration is complete, the ADC performs one new conversion using the new calibration value. 48 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.4.7.5 Calibration Command Procedure Use the following procedure to calibrate using commands. The register-lock mode must be UNLOCK for all calibration commands. After power-on, make sure the reference voltage has stabilized before calibrating. Perform offset calibration before full-scale calibration. 1. Configure the ADC as required. 2. Apply the appropriate calibration signal (zero or full-scale) 3. Take the START pin high or send the START command to start conversions. DRDY is driven high. 4. Before the conversion cycle completes, send the calibration command. Keep CS low otherwise the command is cancelled. Send no other commands during the calibration period. 5. Calibration time depends on the data rate and digital filter mode. See Table 14. DRDY asserts low when calibration is complete. The offset or full-scale calibration registers are updated with new values. At calibration completion, new conversion data are ready using the new calibration value. Table 14. Calibration Time (ms) (1) FILTER MODE (1) DATA RATE (SPS) FIR SINC1 SINC2 SINC3 SINC4 SINC5 2.5 6805 6801 7601 8401 9201 — 5 3405 3401 3801 4201 4601 — 10 1705 1701 1901 2101 2301 — 16.6 — 1021 1141 1261 1381 — 20 854.5 850.9 951.0 1051 1151 — 50 — 340.9 380.9 420.9 460.9 — 60 — 284.2 317.5 350.9 384.2 — 100 — 170.9 190.9 210.9 230.9 — 400 — 43.36 48.36 53.36 58.36 — 1200 — 15.02 16.69 18.36 20.02 — 2400 — 7.938 8.772 9.605 10.44 — 4800 — 4.397 4.813 5.230 5.647 — 7200 — 3.216 3.494 3.772 4.050 — 14400 — — — — — 1.892 19200 — — — — — 1.458 25600 — — — — — 1.133 40000 — — — — — 0.738 Nominal clock frequency. Chop and AC-excitation modes disabled. 9.4.7.6 User Calibration Procedure To user calibrate, apply the calibration voltage, acquire conversion data, and compute the calibration value. The computed value is written to the corresponding calibration registers. Before starting calibration, preset the offset and full-scale registers to 000000h and 400000h, respectively. To offset calibrate, short the ADC inputs (or inputs to the system) and average n number of the conversion results. Averaging conversion data reduces noise to improve calibration accuracy. Write the averaged value of the conversion data to the offset registers. To gain calibrate using a full scale calibration voltage, temporarily reduce the full scale register 95% to avoid output clipped codes (set FSCAL[2:0] to 3CCCCCh). Acquire n number of conversions and average the conversions to reduce noise to improve calibration accuracy. Compute the full-scale calibration value as shown in Equation 7: Full-Scale Calibration Value = Expected Code / Actual Code · 400000h where • Expected code = 799998h using full scale calibration signal and 95% scale factor Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback (7) 49 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.5 Programming 9.5.1 Serial Interface The serial interface is SPI-compatible and is used to read conversion data, configure registers, and control the ADC. The serial interface consists of four control lines: CS, SCLK, DIN, and DOUT/DRDY. Most microcontroller SPI peripherals can operate with the ADC. The interface operates in SPI mode 1, where CPOL = 0 and CPHA = 1. In SPI mode 1, SCLK idles low and data are updated or changed on SCLK rising edges; data are latched or read on SCLK falling edges. Timing details of the SPI protocol are found in Figure 1 and Figure 2. 9.5.1.1 Chip Select (CS) CS is an active-low input that selects the serial interface for communication. CS must be low during the entire data transaction. When CS is taken high, the serial interface resets, SCLK input activity is ignored (blocking commands), and DOUT/DRDY enters the high-impedance state. The operation of DRDY is not effected by CS. If the ADC is a single device connected to the serial bus, CS can be tied low in order to reduce the serial interface to three lines. 9.5.1.2 Serial Clock (SCLK) SCLK is the serial clock input that shifts data into and out of the ADC. Output data are updated on the rising edge of SCLK and input data are latched on the falling edge of SCLK. Return SCLK low after the data operation is completed. SCLK is a Schmidt-triggered input designed to improve noise immunity. Even though SCLK is noise resistant, keep SCLK as noise-free as possible to avoid unintentional SCLK transitions. Avoid ringing and overshoot on the SCLK input. Place a series termination resistor close to the SCLK drive pin to reduce ringing. 9.5.1.3 Data Input (DIN) DIN is the serial data input to the ADC. DIN is used to input commands and register data to the ADC. Data are latched on the falling edge of SCLK. 9.5.1.4 Data Output/Data Ready (DOUT/DRDY) The DOUT/DRDY pin is a dual-function output. The functions of this pin are data output and data ready. The functionality changes automatically based on whether a read data operation is in progress. During a read data operation, the functionality is data output. After the read operation is complete, the functionality changes to data ready. In data output mode, data are updated on the SCLK rising edge, therefore the host latches the data on the falling edge of SCLK. In data-ready mode, the pin functions the same as DRDY (if CS is low) by asserting low when data are ready. Therefore, monitor either DOUT/DRDY or DRDY to determine when data are ready. When CS is high, the DOUT/DRDY pin is in the high-impedance mode (tri-state). 9.5.1.5 Serial Interface Auto-Reset The serial interface is reset by taking CS high. Applications that tie CS low do not have the ability to reset the serial interface by CS. If a false SCLK occurs (for example, caused by a noise pulse or clocking glitch), the serial interface may inadvertently advance one or more bit positions, resulting in loss of synchronization to the host. If loss of synchronization occurs, the ADC interface does not respond correctly until the interface is reset. For applications that tie CS low, the serial interface auto-reset feature recovers the interface in the event that an unintentional SCLK glitch occurs. When the first SCLK low-to-high transition occurs (either caused by a glitch or by normal SCLK activity), seven SCLK transitions must occur within 65536 fCLK cycles (8.9 ms) to complete the byte transaction, otherwise the serial interface resets. After reset, the interface is ready to begin the next byte transaction. If the byte transaction is completed within the 65536 fCLK cycles, the serial interface does not reset. The cycle of SCLK detection re-starts at the next rising edge of SCLK. The serial interface is reset by holding SCLK low for a minimum 65536 fCLK cycles. The auto-reset function is enabled by the SPITIM bit (default is off). See Figure 3 for timing details. 50 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Programming (continued) 9.5.2 Data Ready (DRDY) DRDY is an output that asserts low when conversion data are ready. After power-up, DRDY also indicates when the ADC is ready for communication. The operation of DRDY depends on the conversion mode (continuous or pulse) and whether the conversion data are retrieved or not. Figure 75 shows DRDY operation with and without data retrieval in the two modes of conversion. DRDY - with data retrieval (Continuous-conversion mode) DRDY ± w/o data retrieval (Continuous-conversion mode) DRDY ± w or w/o data retreival (Pulse-conversion mode) START Command START STOP START STOP Figure 75. DRDY Operation 9.5.2.1 DRDY in Continuous-Conversion Mode In continuous-conversion mode, DRDY is driven high when conversions are started and is driven low when conversion data are ready. During data readback, DRDY returns high at the end of the read operation. If the conversion data are not read, DRDY pulses high 16 fCLK cycles prior to the next falling edge. To read conversion data before the next conversion is ready, send the complete read-data command 16 fCLK cycles before the next DRDY falling edge. If the readback command is sent less than 16 fCLK cycles before the DRDY falling edge, either old or new conversion data are provided, depending on the timing of when the command is sent. In the case that old conversion data are provided, DRDY driven low is delayed until after the read data operation is completed. In this case, the DRDY bit of the STATUS byte is cleared to indicate the same data have been read. If new conversion data are provided, DRDY transitions low at the normal period of the data rate. In this case, the DRDY bit of the STATUS byte is set to indicate that new data have been read. To make sure new data are read back, wait until DRDY asserts low before starting the data read operation. 9.5.2.2 DRDY in Pulse-Conversion Mode DRDY is driven high at conversion start and is driven low when the conversion data are ready. During the data read operation DRDY remains low until a new conversion is started. 9.5.2.3 Data Ready by Software Polling Use software polling of data ready in lieu of hardware polling of DRDY or DOUT/DRDY. To software poll, read the STATUS register and poll the DRDY bit. In order to not skip conversion data in continuous conversion mode, poll the bit at least as often as the period of the data rate. If the DRDY bit is set, then conversion data are new since the previous data read operation. If the bit is cleared, conversion data are not new since the previous data read operation. In this case, the previous conversion data are returned. 9.5.3 Conversion Data Conversion data are read by the RDATA command. To read data, take CS low and issue the read data command. The data field response consists of the optional STATUS byte, three data bytes, and the optional CRC byte. The CRC is computed over the combination of status byte and conversion data bytes. See the RDATA Command section for details to read conversion data. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 51 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Programming (continued) 9.5.3.1 Status byte (STATUS) The status byte contains information on the operating state of the ADC. The STATUS byte is included with the conversion data by enabling bit STATENB of register MODE3. Optionally, read the STATUS register directly to read status information without the need to read conversion data. See Figure 81 for details. 9.5.3.2 Conversion Data Format The conversion data are 24 bits, in two's-complement format to represent positive and negative values. The data output begins with the most significant bit (sign bit) first. The data are scaled so that VIN = 0 V results in an uncalibrated code value of 000000h; positive full scale equals 7FFFFFh and negative full scale equals 800000h; see Table 15 for the uncalibrated code values. The data are clipped to 7FFFFFh (positive full scale) and 800000h (negative full scale) during positive and negative signal overdrive, respectively. Table 15. ADC Conversion Data Codes DESCRIPTION Positive full scale 1 LSB INPUT SIGNAL (V) 23 ≥ VREF / Gain · (2 000001h 000000h 23 –VREF / (Gain · 2 (1) 7FFFFFh 0 ) FFFFFFh ≤ –VREF / Gain Negative full scale (1) - 1) / 2 VREF / (Gain · 223 ) Zero scale -1 LSB 24-BIT CONVERSION DATA 23 800000h Ideal (calibrated) conversion data. 9.5.4 CRC Cyclic redundancy check (CRC) is an error checking code that detects communication errors to and from the host. CRC is the division remainder of the data payload bytes by a fixed polynomial. The data payload is 1, 2, 3 or 4 bytes depending on the data operation. The CRC mode is optional and is enabled by the CRCENB bit. See Table 35 to program the CRC mode. The user computes the CRC corresponding to the two command bytes and appends the CRC to the command string (3rd byte). A 4th, zero-value byte completes the command field. The ADC repeats the CRC calculation and compares the calculation to the received CRC. If the user and repeated CRC values match, the command executes and the ADC responds by transmitting the repeated CRC during the 4th byte of the command. If the operation is conversion data or register data read, the ADC responds with a 2nd CRC that is computed over the requested data payload bytes. The response data payload is 1, 3, or 4 bytes depending on the data operation. If the user and repeated CRC values do not match, the command does not execute and the ADC responds with an inverted CRC for the actual received command bytes. The inverted CRC is intended to signal the host of the failed operation. The user terminates transmission of the command bytes to match the action of ADC termination. The CRCERR bit is set in the STATUS register when a CRC error is detected. The ADC is ready to accept the next command after a CRC error occurs at the end of the 4th byte. The CRC data byte is the 8-bit remainder of the bitwise exclusive-OR (XOR) operation of the argument by a CRC polynomial. The CRC polynomial is based on the CRC-8-ATM (HEC): X8 + X2 + X1 + 1. The nine binary polynomial coefficients are: 100000111. The CRC calculation is preset with "1" data values. The CRC mnemonics apply to the following command sections. • CRC-2: Input CRC of command bytes 1 and 2. Except for WREG command, the value of byte 2 is arbitrary • Out CRC-1: Output CRC of one register data byte • Out CRC-2: Output CRC of two command bytes, inverted value if input CRC error detected • Out CRC-3: Output CRC of three conversion data bytes • Out CRC-4: Output CRC of three conversion data bytes plus STATUS byte • Echo Byte 1: Echo of received input byte 1 • Echo Byte 2: Echo of received input byte 2 52 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.5.5 Commands Commands read conversion data, control the ADC, and read and write register data. See Table 16 for the list of commands. Send only the commands that are listed in Table 16. The ADC executes commands at completion of the 2nd byte (no CRC verification) or at completion of the 4th byte (with CRC verification). Follow the two byte or four byte format according to the CRC mode. Except for register write commands, the value of the second command byte is arbitrary but the value is included in the CRC calculation (total of two-byte CRC). If a CRC error is detected, the ADC does not execute the command. Taking CS high before the command is completed results in termination of the command. When CS is taken low, the communication frame is reset to start a new command. Table 16. Command Byte Summary MNEMONIC DESCRIPTION BYTE 1 BYTE 2 BYTE 3 (CRC Mode Only) BYTE 4 (CRC Mode only) Control Commands NOP No operation 00h Arbitrary CRC-2 00h RESET Reset 06h Arbitrary CRC-2 00h START Start conversion 08h Arbitrary CRC-2 00h STOP Stop conversion 0Ah Arbitrary CRC-2 00h 12h Arbitrary CRC-2 00h Read Data Command RDATA Read conversion data Calibration Commands SYOCAL System offset calibration 16h Arbitrary CRC-2 00h GANCAL Gain calibration 17h Arbitrary CRC-2 00h SFOCAL Self offset calibration 19h Arbitrary CRC-2 00h Register Commands RREG Read register data 20h + rrh (1) Arbitrary CRC-2 00h WREG Write register data 40h + rrh (1) Register data CRC-2 00h Protection Commands LOCK Register lock F2h Arbitrary CRC-2 00h UNLOCK Register unlock F5h Arbitrary CRC-2 00h (1) rrh = 5-bit register address. 9.5.5.1 NOP Command This command is no operation. Use the NOP command to validate the CRC response byte and error detection without affecting normal operation. Table 17 shows the NOP command byte sequence. Table 17. NOP Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 No CRC mode DIN 00h Arbitrary DOUT/DRDY FFh Echo byte 1 CRC mode DIN 00h Arbitrary CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo byte 2 Out CRC-2 Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 53 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.5.5.2 RESET Command The RESET command resets ADC operation and resets the registers to default values. See the Reset by Command section for details. Table 18 shows the RESET command byte sequence. Table 18. RESET Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 No CRC mode DIN 06h Arbitrary DOUT/DRDY FFh Echo byte 1 CRC mode DIN 06h Arbitrary CRC-2 00H DOUT/DRDY FFh Echo byte 1 Echo byte 2 Out CRC-2 9.5.5.3 START Command This command starts conversions. See the Conversion Control section for details. Table 19 shows the START command byte sequence. Table 19. START Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 DIN 08h Arbitrary DOUT/DRDY FFh Echo byte 1 DIN 08h Arbitrary CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo byte 2 Out CRC-2 No CRC mode CRC mode 9.5.5.4 STOP Command This command stops conversions. See the Conversion Control section for details. Table 20 shows the STOP command byte sequence. Table 20. STOP Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 No CRC mode DIN 0Ah Arbitrary DOUT/DRDY FFh Echo byte 1 CRC mode DIN 0Ah Arbitrary CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo byte 2 Out CRC-2 9.5.5.5 RDATA Command This command reads conversion data. Because the data are buffered, the data can be read at any time during the conversion phase. If data are read near the completion of the next conversion, old or new conversion data are returned. See the Data Ready (DRDY) section for details. The response of conversion data varies in length from 3 to 5 bytes depending if the STATUS byte and CRC bytes are included. See the Conversion Data Format section for the numeric data format. See Table 21, Figure 76 (minimum configuration) and Figure 77 (maximum configuration) for operation of the RDATA command. 54 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Table 21. RDATA Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5 BYTE 6 BYTE 7 BYTE 8 BYTE 9 No CRC mode DIN 12h Arbitrary DOUT/DRDY FFh Echo byte 1 00h STATUS (1) 00h 00h 00h MSB data MID data LSB data CRC mode DIN 12h Arbitrary CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo byte 2 Out CRC-2 (1) 00h STATUS (1) 00h 00h 00h 00h MSB data MID data LSB data Out CRC-3 or Out CRC-4 Optional STATUS byte CS (1) 1 9 17 25 33 SCLK DIN 12h FFh DOUT/DRDY 00h 00h 00h MSB data MID data LSB data Arbitrary Echo byte 1 NOTE: CS can be tied low Figure 76. Conversion Data Read Operation (STATUS Byte and CRC Mode Disabled) (1) CS 1 9 17 25 41 33 49 57 65 SCLK DIN 12h DOUT/DRDY FFh Arbitrary Echo byte 1 CRC-2 00h 00h Echo byte 2 Out CRC-2 STATUS 00h 00h MID data MSB data 00h 00h LSB DATA Out CRC-4 NOTE: CS can be tied low Figure 77. Conversion Data Read Operation (STATUS Byte and CRC Mode Enabled) 9.5.5.6 SYOCAL Command This command is used for system offset calibration. See the Offset System-Calibration (SYOCAL) section for details. Table 22 shows the SYOCAL command byte sequence. Table 22. SYOCAL Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 No CRC mode DIN 16h Arbitrary DOUT/DRDY FFh Echo byte 1 CRC mode DIN 16h Arbitrary CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo Byte 2 Out CRC-2 Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 55 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.5.5.7 GANCAL Command This command is for gain calibration. See the Full-Scale Calibration (GANCAL) section for details. Table 23 shows the GANCAL command byte sequence. Table 23. GANCAL Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 No CRC mode DIN 17h Arbitrary DOUT/DRDY FFh Echo byte 1 CRC mode DIN 17h Arbitrary CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo Byte 2 Out CRC-2 9.5.5.8 SFOCAL Command This command is used for self offset calibration. See the Offset Self-Calibration (SFOCAL) section for details. Table 24 shows the SFOCAL command byte sequence. Table 24. SFOCAL Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 DIN 19h Arbitrary DOUT/DRDY FFh Echo byte 1 DIN 19h Arbitrary CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo Byte 2 Out CRC-2 No CRC mode CRC mode 9.5.5.9 RREG Command Use the RREG command to read register data. The register data are read one byte at a time by issuing the RREG command for each operation. Add the register address (rrh) to the base opcode (20h) to construct the command byte (20h + rrh). Table 25 illustrates the command byte sequence. The ADC responds with the register data byte, most significant bit first. The response to registers outside the valid address range is 00h. Figure 78 shows an example of the register read operation. The Out CRC-1 byte is the CRC calculated for the register data byte. Table 25. RREG Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5 BYTE 6 No CRC mode DIN 20h + rrh (1) Arbitrary 00h DOUT/DRDY FFh Echo byte 1 Register data CRC mode DIN 20h + rrh Arbitrary CRC-2 00h 00h 00h DOUT/DRDY FFh Echo byte 1 Echo byte 2 Out CRC-2 Register data Out CRC-1 (1) 56 rrh = 5-bit register address Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 (1) CS 1 9 17 25 33 41 SCLK DIN 22h Arbitrary CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo byte 2 Out CRC-2 (1) 00h 00h Reg data Out CRC-1 CS can be tied low Figure 78. Register Read Operation (address = 02h, CRC Mode Enabled) 9.5.5.10 WREG Command Use the WREG command to write register data. The register data are written one byte at a time by issuing the WREG command for each operation. Add the register address (rrh) to the base opcode (40h) to construct the command byte (40h + rrh). Table 26 shows the command byte sequence. Figure 79 shows an example of the WREG operation. Be aware that writing to certain registers results in conversion restart. Table 29 lists the registers that restart an ongoing conversion when written to. Do not write to registers outside the address range. Table 26. WREG Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 DIN 40h + rrh (1) Register data DOUT/DRDY FFh Echo byte 1 DIN 40h + rrh Register data CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo byte 2 Out CRC-2 No CRC mode CRC mode (1) rrh = 5-bit register address. (1) CS 1 9 17 25 SCLK DIN 42h DOUT/DRDY A. FFh Reg Data CRC-2 00h Echo byte 1 Echo byte 2 Out CRC-2 CS can be tied low Figure 79. Register Write Operation (address = 02h, CRC Mode Enabled) Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 57 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.5.5.11 LOCK Command The LOCK command locks-out write access to the registers including the calibration registers that are changed by calibration commands. The default mode is UNLOCK. Read access is allowed in LOCK mode. Table 27 shows the LOCK command byte sequence. Table 27. LOCK Command DIRECTION BYTE 1 BYTE 2 BYTE 3 BYTE 4 No CRC mode DIN F2h Arbitrary DOUT/DRDY FFh Echo byte 1 CRC mode DIN F2h Arbitrary CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo Byte2 out CRC-2 9.5.5.12 UNLOCK Command The UNLOCK command allows register write access, including access to the contents of the calibration registers that can be changed by the calibration commands. Table 28 shows the UNLOCK command byte sequence. Table 28. UNLOCK Command DIRECTION BYTE 1 BYTE 2 DIN F5h Arbitrary DOUT/DRDY FFh Echo byte 1 BYTE 3 BYTE 4 No CRC mode CRC mode 58 DIN F5h Arbitrary CRC-2 00h DOUT/DRDY FFh Echo byte 1 Echo Byte2 Out CRC-2 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.6 Register Map The register map consists of 19, one-byte registers. Collectively, the registers are used to configure the ADC to the desired operating mode. Access the registers by using the RREG and WREG (read-register and writeregister) commands. Register data are accessed one register byte at a time for each command operation. At power-on or device reset, the registers are reset to the default values, as shown in the Default column of Table 29. Writing new data to certain registers causes the ADC conversion in progress to restart. These registers are listed in the Restart column in Table 29. Register-write access is enabled or disabled by the UNLOCK and LOCK commands, respectively. The default mode is register UNLOCK. See the LOCK Command section for more details. Table 29. Register Map Summary (rrh) REGISTER DEFAULT RESTART 00h ID xxh BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 01h STATUS 01h 02h MODE0 24h Yes 03h MODE1 01h Yes 04h MODE2 00h 05h MODE3 00h 06h REF 05h 07h OFCAL0 00h 08h OFCAL1 00h OFC[15:8] 09h OFCAL2 00h OFC[23:16] 0Ah FSCAL0 00h FSC[7:0] 0Bh FSCAL1 00h FSC[15:8] 0Ch FSCAL2 40h 0Dh IMUX FFh IMUX2[3:0] IMUX1[3:0] 0Eh IMAG 00h IMAG2[3:0] IMAG1[3:0] 0Fh RESERVED 00h 10h PGA 00h Yes 11h INPMUX FFh Yes 12h INPBIAS 00h Yes DEV_ID[3:0] LOCK CRCERR BIT 1 PGAL_ALM PGAH_ALM REFL_ALM DRDY DR[4:0] 0 CHOP[1:0] CLOCK RESET FILTER[2:0] CONVRT DELAY[3:0] GPIO_CON[3:0] GPIO_DIR[3:0] PWDN STATENB CRCENB SPITIM 0 0 0 REFENB Yes BIT 0 REV_ID[3:0] GPIO_DAT[3:0] RMUXP[1:0] RMUXN[1:0] OFC[7:0] FSC[23:16] 00h BYPASS 0 0 0 0 MUXP[3:0] 0 0 GAIN[2:0] MUXN[3:0] 0 VBIAS BOCSP BOCS[2:0] 9.6.1 Device Identification (ID) Register (address = 00h) [reset = xxh] Figure 80. ID Register 7 6 5 4 3 2 DEV_ID[3:0] 1 0 REV_ID[3:0] NOTE: Reset values are device dependent LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 30. ID Register Field Descriptions Bit Field Type Reset Description 7:4 DEV_ID[3:0] R xh Device ID 1000: ADS1261, ADS1261B 1010: ADS1260B 3:0 REV_ID[3:0] R xh Revision ID Note: Revision ID can change without notification Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 59 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.6.2 Device Status (STATUS) Register (address = 01h) [reset = 01h] Figure 81. STATUS Register 7 LOCK R-0h 6 CRCERR R/W-0h 5 PGAL_ALM R-0h 4 PGAH_ALM R-0h 3 REFL_ALM R-0h 2 DRDY R-0h 1 CLOCK R-xh 0 RESET R/W-1h LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 31. STATUS Register Field Descriptions Bit Field Type Reset Description 7 LOCK R 0h Register Lock Status Indicates register lock status. Register writes are locked by the LOCK command and unlocked by the UNLOCK command. 0: Register write not locked (default) 1: Register write locked 6 CRCERR R/W 0h CRC Error Indicates that a CRC error is detected by the ADC. The CRC error bit remains set until cleared by the user. 0: No CRC error 1: CRC error 5 PGAL_ALM R 0h PGA Low Alarm Indicates PGA output voltage is below the low limit. The alarm resets at the start of conversion cycles. 0: No Alarm 1: Alarm 4 PGAH_ALM R 0h PGA High Alarm Indicates PGA output voltage is above the high limit. The alarm resets at the start of conversion cycles. 0: No Alarm 1: Alarm 3 REFL_ALM R 0h Reference Low Alarm Indicates reference voltage is below the low limit. The alarm resets at the start of conversion cycles. 0: No Alarm 1: Alarm 2 DRDY R 0h Data Ready Indicates conversion data ready. 0: Conversion data not new since the previous read operation 1: Conversion data new since the previous read operation 1 CLOCK R xh Clock Indicates internal or external clock mode. The ADC automatically selects the clock source. 0: ADC clock is internal 1: ADC clock is external 0 RESET R/W 1h Reset Indicates ADC reset. Clear the bit to detect next device reset. 0: No reset 1: Reset (default) 60 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.6.3 Mode 0 (MODE0) Register (address = 02h) [reset = 24h] Figure 82. MODE0 Register 7 6 5 DR[4:0] R/W-4h 4 3 2 1 FILTER[2:0] R/W-4h 0 LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 32. MODE0 Register Field Descriptions Bit Field Type Reset Description 7:3 DR[4:0] R/W 4h Data Rate Select the ADC data rate. 00000: 2.5 SPS 00001: 5 SPS 00010: 10 SPS 00011: 16.6 SPS 00100: 20 SPS (default) 00101: 50 SPS 00110: 60 SPS 00111: 100 SPS 01000: 400 SPS 01001: 1200 SPS 01010: 2400 SPS 01011: 4800 SPS 01100: 7200 SPS 01101: 14400 SPS 01110: 19200 SPS 01111: 25600 SPS 10000 - 11111: 40000 SPS (fCLK = 10.24 MHz) 2:0 FILTER[2:0] R/W 4h Digital Filter Select the digital filter mode. 000: sinc1 001: sinc2 010: sinc3 011: sinc4 100: FIR (default) 101: Reserved 110: Reserved 111: Reserved Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 61 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.6.4 Mode 1 (MODE1) Register (address = 03h) [reset = 01h] Figure 83. MODE1 Register 7 0 R/W-0h 6 5 4 CONVRT R/W-0h CHOP[1:0] R/W-0h 3 2 1 0 DELAY[3:0] R/W-1h LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 33. MODE1 Register Field Descriptions Bit 7 Field Type Reset Description 0 R/W 0h Reserved CHOP[1:0] R/W 0h Always write 0 6:5 Chop and AC-Excitation Modes Select the Chop and AC-excitation modes. 00: Normal mode (default) 01: Chop mode 10: 2-wire AC-excitation mode ( ADS1261 only) 11: 4-wire AC-excitation mode ( ADS1261 only) 4 CONVRT R/W 0h ADC Conversion Mode Select the ADC conversion mode. 0: Continuous conversions (default) 1: Pulse (one shot) conversion 3:0 DELAY[3:0] R/W 1h Conversion Start Delay Program the time delay at conversion start. Delay values are with fCLK = 7.3728 MHz. 0000: 0 µs (not for 25600 SPS or 40000 SPS operation) 0001: 50 µs (default) 0010: 59 µs 0011: 67 µs 0100: 85 µs 0101: 119 µs 0110: 189 µs 0111: 328 µs 1000: 605 µs 1001: 1.16 ms 1010: 2.27 ms 1011: 4.49 ms 1100: 8.93 ms 1101: 17.8 ms 1110: Reserved 1111: Reserved 62 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.6.5 Mode 2 (MODE2) Register (address = 04h) [reset = 00h] Figure 84. MODE2 Register 7 6 5 4 3 2 GPIO_CON[3:0] R/W-0h 1 0 GPIO_DIR[3:0] R/W-0h LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 34. MODE2 Register Field Descriptions (1) Bit 7 Field Type Reset Description GPIO_CON[3] R/W 0h GPIO3 Pin Connection Connect GPIO3 to analog input AIN5. 0: GPIO3 not connected to AIN5 (default) 1: GPIO3 connected to AIN5 6 GPIO_CON[2] R/W 0h GPIO2 Pin Connection Connect GPIO2 to analog input AIN4. 0: GPIO2 not connected to AIN4 (default) 1: GPIO2 connected to AIN4 5 GPIO_CON[1] R/W 0h GPIO1 Pin Connection Connect GPIO1 to analog input AIN3. 0: GPIO1 not connected to AIN3 (default) 1: GPIO1 connected to AIN3 4 GPIO_CON[0] R/W 0h GPIO0 Pin Connection Connect GPIO0 to analog input AIN2 0: GPIO0 not connected to AIN2 (default) 1: GPIO0 connected to AIN2 3 GPIO_DIR[3] R/W 0h GPIO3 Pin Direction Configure GPIO3 as a GPIO input or GPIO output on AIN5. 0: GPIO3 is an output (default) 1: GPIO3 is an input 2 GPIO_DIR[2] R/W 0h GPIO2 Pin Direction Configure GPIO2 as a GPIO input or GPIO output on AIN4. 0: GPIO2 is an output (default) 1: GPIO2 is an input 1 GPIO_DIR[1] R/W 0h GPIO1 Pin Direction Configure GPIO1 as a GPIO input or GPIO output on AIN3. 0: GPIO1 is an output (default) 1: GPIO1 is an input 0 GPIO_DIR[0] R/W 0h GPIO0 Pin Direction Configure GPIO0 as a GPIO input or GPIO output on AIN2. 0: GPIO0 is an output (default) 1: GPIO0 is an input (1) ADS1261 and ADS1261B only. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 63 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.6.6 Mode 3 (MODE3) Register (address = 05h) [reset = 00h] Figure 85. MODE3 Register 7 PWDN R/W-0h 6 STATENB R/W-0h 5 CRCENB R/W-0h 4 SPITIM R/W-0h 3 2 1 0 GPIO_DAT[3:0] R/W-0h LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 35. MODE3 Register Field Descriptions Bit 7 Field Type Reset Description PWDN R/W 0h Software Power-down Mode Select the software power-down mode. 0: Normal mode (default) 1: Software power-down mode 6 STATENB R/W 0h STATUS Byte Enable the Status byte for the conversion data read operation. 0: No Status byte (default) 1: Status byte enabled 5 CRCENB R/W 0h CRC Data Verification Enable CRC data verification. 0: No CRC (default) 1: CRC enabled 4 SPITIM R/W 0h SPI Auto-Reset Function Enable the SPI auto-reset function. 0: SPI auto-reset disabled (default) 1: SPI auto-reset enabled 3 GPIO_DAT[3] (1) R/W 0h GPIO3 Data Read or write the GPIO3 data on AIN5. 0: GPIO3 is low (default) 1: GPIO3 is high 2 GPIO_DAT[2] (1) R/W 0h GPIO2 Data Read or write the GPIO2 data on AIN4. 0: GPIO2 is low (default) 1: GPIO2 is high 1 GPIO_DAT[1] (1) R/W 0h GPIO1 Data Read or write the GPIO1 data on AIN3. 0: GPIO1 is low (default) 1: GPIO1 is high 0 GPIO_DAT[0] (1) R/W 0h GPIO0 Data Read or write the GPIO1 data on AIN3. 0: GPIO0 is low (default) 1: GPIO0 is high (1) 64 ADS1261 and ADS1261B only. Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.6.7 Reference Configuration (REF) Register (address = 06h) [reset = 05h] Figure 86. REF Register 7 0 R/W-0h 6 0 R/W-0h 5 0 R/W-0h 4 REFENB R/W-0h 3 2 1 RMUXP[1:0] R/W-1h 0 RMUXN[1:0] R/W-1h LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 36. REF Register Field Descriptions Bit Field Type Reset Description 7:5 0 R/W 0h Reserved REFENB R/W 0h Always write 0h 4 Internal Reference Enable Enable the internal reference. 0: Internal reference disabled (default) 1: Internal reference enabled 3:2 RMUXP[1:0] R/W 1h Reference Positive Input Select the positive reference input. 00: Internal reference positive 01: AVDD internal (default) 10: AIN0 external 11: AIN2 external ( ADS1261 only) 1:0 RMUXN[1:0] R/W 1h Reference Negative Input Select the negative reference input. 00: Internal reference negative 01: AVSS internal (default) 10: AIN1 external 11: AIN3 external ( ADS1261 only) Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 65 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.6.8 Offset Calibration (OFCALx) Registers (address = 07h, 08h, 09h) [reset = 00h, 00h, 00h] Figure 87. OFCAL0, OFCAL1, OFCAL2 Registers 7 6 5 4 3 2 1 0 11 10 9 8 19 18 17 16 OFC[7:0] R/W-00h 15 14 13 12 OFC[15:8] R/W-00h 23 22 21 20 OFC[23:16] R/W-00h LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 37. OFCAL0, OFCAL1, OFCAL2 Registers Field Description Bit 23:0 Field Type Reset Description OFC[23:0] R/W 000000h Offset Calibration These three registers are the 24-bit offset calibration word. The offset calibration is two's complement format. The ADC subtracts the offset value from the conversion result before the full-scale operation. 9.6.9 Full-Scale Calibration (FSCALx) Registers (address = 0Ah, 0Bh, 0Ch) [reset = 00h, 00h, 40h] Figure 88. FSCAL0, FSCAL1, FSCAL2 Registers 7 6 5 4 3 2 1 0 11 10 9 8 19 18 17 16 FSC[7:0] R/W-00h 15 14 13 12 FSC[15:8] R/W-00h 23 22 21 20 FSC[23:16] R/W-40h LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 38. FSCAL0, FSCAL1, FSCAL2 Registers Field Description Bit 23:0 Field Type Reset Description FSC[23:0] R/W 400000h Full-Scale Calibration These three registers are the 24-bit full scale calibration word. The full-scale calibration is straight binary format. The ADC divides the register value by 400000h then multiplies the result with the conversion data. The scaling operation occurs after the offset operation. 66 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.6.10 IDAC Multiplexer (IMUX) Register (address = 0Dh) [reset = FFh] Figure 89. IMUX Register 7 6 5 4 3 2 IMUX2[3:0] R/W-Fh 1 0 IMUX1[3:0] R/W-Fh LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 39. IMUX Register Field Descriptions Bit Field Type Reset Description 7:4 IMUX2[3:0] R/W Fh IDAC2 Output Multiplexer Select the IDAC2 analog input pin connection. 0000: AIN0 0001: AIN1 0010: AIN2 0011: AIN3 0100: AIN4 0101: AIN5 ( ADS1261 only) 0110: AIN6 ( ADS1261 only) 0111: AIN7 ( ADS1261 only) 1000: AIN8 ( ADS1261 only) 1001: AIN9 ( ADS1261 only) 1010: AINCOM 1011: No connection 1100: No connection 1101: No connection 1110: No connection 1111: No connection (default) 3:0 IMUX1[3:0] R/W Fh IDAC1 Output Multiplexer Select the IDAC1 analog input pin connection. 0000: AIN0 0001: AIN1 0010: AIN2 0011: AIN3 0100: AIN4 0101: AIN5 ( ADS1261 only) 0110: AIN6 ( ADS1261 only) 0111: AIN7 ( ADS1261 only) 1000: AIN8 ( ADS1261 only) 1001: AIN9 ( ADS1261 only) 1010: AINCOM 1011: No connection 1100: No connection 1101: No connection 1110: No connection 1111: No connection (default) Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 67 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.6.11 IDAC Magnitude (IMAG) Register (address = 0Eh) [reset = 00h] Figure 90. IMAG Register 7 6 5 4 3 2 IMAG2[3:0] R/W-0h 1 0 IMAG1[3:0] R/W-0h LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 40. IMAG Register Field Descriptions Bit Field Type Reset Description 7:4 IMAG2[3:0] R/W 0h IDAC2 Current Magnitude Select the magnitude of current source IDAC2. 0000: Off (default) 0001: 50 µA 0010: 100 µA 0011: 250 µA 0100: 500 µA 0101: 750 µA 0110: 1000 µA 0111: 1500 µA 1000: 2000 µA 1001: 2500 µA 1010: 3000 µA 1011: Off 1100: Off 1101: Off 1110: Off 1111: Off 3:0 IMAG1[3:0] R/W 0h IDAC1 Current Magnitude Select the magnitude of current source IDAC1. 0000: Off (default) 0001: 50 µA 0010: 100 µA 0011: 250 µA 0100: 500 µA 0101: 750 µA 0110: 1000 µA 0111: 1500 µA 1000: 2000 µA 1001: 2500 µA 1010: 3000 µA 1011: Off 1100: Off 1101: Off 1110: Off 1111: Off 68 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.6.12 Reserved (RESERVED) Register (address = 0Fh) [reset = 00h] Figure 91. RESERVED Register 7 0 R-0h 6 0 R-0h 5 0 R-0h 4 0 R-0h 3 0 R-0h 2 0 R-0h 1 0 R-0h 0 0 R-0h LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 41. RESERVED Register Field Descriptions Bit Field Type Reset Description 7:0 0 R 0h Reserved These bits are read only and always return 0 9.6.13 PGA Configuration (PGA) Register (address = 10h) [reset = 00h] Figure 92. PGA Register 7 BYPASS R/W-0h 6 0 R/W-0h 5 0 R/W-0h 4 0 R/W-0h 3 0 R/W-0h 2 1 GAIN[2:0] R/W-0h 0 LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 42. PGA Register Field Descriptions Bit 7 Field Type Reset Description BYPASS R/W 0h PGA Bypass Mode Select the PGA mode. 0: PGA mode (default) 1: PGA bypass 6:3 0 R/W 0h 2:0 GAIN[2:0] R/W 0h Reserved Always write 0 Gain Select the gain. 000: 1 (default) 001: 2 010: 4 011: 8 100: 16 101: 32 110: 64 111: 128 Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 69 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 9.6.14 Input Multiplexer (INPMUX) Register (address = 11h) [reset = FFh] Figure 93. INPMUX Register 7 6 5 4 3 2 MUXP[3:0] R/W-Fh 1 0 MUXN[3:0] R/W-Fh LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 43. INPMUX Register Field Descriptions Bit Field Type Reset Description 7:4 MUXP[3:0] R/W Fh Positive Input Multiplexer Select the positive multiplexer input. 0000: AINCOM 0001: AIN0 0010: AIN1 0011: AIN2 0100: AIN3 0101: AIN4 0110: AIN5 ( ADS1261 only) 0111: AIN6 ( ADS1261 only) 1000: AIN7 ( ADS1261 only) 1001: AIN8 ( ADS1261 only) 1010: AIN9 ( ADS1261 only) 1011: Internal temperature sensor positive 1100: Internal (AVDD - AVSS) / 4 positive 1101: Internal (DVDD / 4) positive 1110: Inputs open 1111: Internal connection to VCOM (default) 3:0 MUXN[3:0] R/W Fh Negative Input Multiplexer Select the negative multiplexer input. 0000: AINCOM 0001: AIN0 0010: AIN1 0011: AIN2 0100: AIN3 0101: AIN4 0110: AIN5 ( ADS1261 only) 0111: AIN6 ( ADS1261 only) 1000: AIN7 ( ADS1261 only) 1001: AIN8 ( ADS1261 only) 1010: AIN9 ( ADS1261 only) 1011: Internal temperature sensor negative 1100: Internal (AVDD - AVSS) / 4 negative 1101: Internal (DVDD / 4) negative 1110: All inputs open 1111: Internal connection to VCOM (default) 70 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 9.6.15 Input Bias (INPBIAS) Register (address = 12h) [reset = 00h] Figure 94. INPBIAS Register 7 0 R/W-0h 6 0 R/W-0h 5 0 R/W-0h 4 VBIAS R/W-0h 3 BOCSP R/W-0h 2 1 BOCS[2:0] R/W-0h 0 LEGEND: R/W = Read/Write; R = Read only; -n = value after reset Table 44. INPBIAS Register Field Descriptions Bit Field Type Reset Description 7:5 0 R/W 0h Reserved VBIAS R/W 0h Always write 0 4 VBIAS Select the VBIAS connection to the AINCOM pin. 0: VBIAS disabled (default) 1: VBIAS enabled 3 BOCSP R/W 0h Burn-Out Current Source Polarity Select the burn-out current source polarity. 0: Pull-up mode (default) 1: Pull-down mode 2:0 BOCS[2:0] R/W 0h Burn-Out Current Source Magnitude Select the burn-out current source magnitude. 000: Off (default) 001: 50 nA 010: 200 nA 011: 1 µA 100: 10 µA 101: Reserved 110: Reserved 111: Reserved Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 71 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 10 Application and Implementation NOTE Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality. 10.1 Application Information 10.1.1 Input Range In PGA mode, the input voltage must be within the specified input range for linear operation. The following exercise shows how to use Equation 5 to verify the input voltage is within specification. The exercise is a thermocouple with the negative lead connected to AINCOM and the level-shift voltage enabled (2.5 V). The gain factor = 32 and the ADC is powered by a single 5-V power supply. The summary of conditions are: • VAINN = Negative absolute input voltage = 2.5 V • VAINP = Positive absolute input voltage = 2.56 V • VIN = Differential input voltage = 60 mV • AVDD = 4.75 V (worst-case minimum) • AVSS = 0 V • Gain = 32 Evaluation of the equation results in: 1.23 V < 2.5 V and 2.56 V < 3.52 V The inequality is satisfied, therefore the absolute input voltages are within the specified PGA input range. The input requirement can also be verified by measuring the PGA output voltages (pins CAPP and CAPN) with a voltmeter. Check that both outputs are within the range: AVSS + 0.3 V < V(CAPP) and V(CAPN) < AVDD – 0.3 V, under the worst-case input and power-supply conditions. 10.1.2 Input Overload Observe the input overvoltage precautions as outlined in the ESD Diodes section. If an overvoltage condition occurs on an unused channel, the overvoltage channel may crosstalk to the measurement channel. One solution is to externally clamp the inputs with low-forward voltage diodes as shown in Figure 95. The external diodes divert the overvoltage current around the ADC inputs to the power supply and ground. Be aware of the reverse leakage current of the Schottky diodes that may lead to measurement errors. IFAULT Schottky Diode RLIM 5V AVDD AINx ADC AVSS ± 0.3 V > VCLAMP > AVDD + 0.3 V Schottky Diode AVSS IFAULT Figure 95. External Diode Clamps 72 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Application Information (continued) 10.1.3 Burn-out Current Source When using the burn-out current sources, be aware of the offset error caused by the currents flowing through impedances in the input path, including the multiplexer resistance RMUX), external filter resistors and the internal impedance of the sensor REXT), as shown in Figure 96. In many cases, the offset error can be calibrated. Be aware that the combination of chop mode and high data rates increases the input current to the PGA. The increased input current can affect the accuracy of the burn-out current sources. AVDD REXT VSENSOR + ± REXT IBOCS AINx RMUX AINx RMUX VIN = VSENSOR + VOFFSET PGA IBOCS AVSS Figure 96. Burn-Out Current Source Offset Voltage Error 10.1.4 Unused Inputs and Outputs • Analog Inputs To minimize input leakage of the measurement channel, tie unused inputs to mid-supply voltage (AVDD + AVSS) / 2 or to AVDD. • Digital I/O Not all the digital I/Os may be needed to operate the ADC. Be sure not to float both used and unused digital inputs, including during power-down mode. The following is a summary of the optional digital I/Os connection: • CS: Tie CS low to permanently enable the serial interface. • CLKIN: Tie CLKIN to DGND to permanently operate the ADC with the internal oscillator. • START: Tie START to DGND to control conversions by command. Tie START to DVDD to permanently free-run conversions (Continuous-conversion mode only) • RESET: Tie RESET to DVDD if not using hardware reset. The ADC is reset at power-on. The ADC is also reset by the RESET command. • PWDN: Tie PWDN to DVDD if not using the hardware power-down mode. The ADC can be powered down by software. • DRDY: The functionality of the DRDY output is also provided by the dual-mode DOUT/DRDY pin. The DOUT/DRDY output is active when CS is low. Data ready is also determined by software polling. Because the conversion data are buffered, data can be read at any time without the need to synchronize to data ready. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 73 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Application Information (continued) 10.1.5 AC-Excitation Figure 97 shows a example of an AC-excited bridge measurement system. The example shown omits optional filter components for clarity. The transistors switch the bridge excitation voltage by drive signals provided by the GPIO drivers through the analog input pins. The timing of the drive signals are synchronized to the ADC conversions. The drive signals do not overlap in order to avoid bridge commutation during the switching phase of the drive signal. The transistors gate resistors bias the transistors off at power-on. At host start-up, the host configures the ADC to the AC-excitation mode. See Figure 7 for timing of the drive signals. 5V AVDD 5V ADS1261 100N Ÿ AIN2 AIN5 (ACX1) (ACX2) 100N Ÿ AIN0 SEN + SIG + AIN6 SIG - AIN7 SEN - AIN1 (REFP0) (AINP) (AINN) (REFN0) 5V 100N Ÿ AIN3 AIN4 (ACX2) (ACX1) 100N Ÿ AVSS Figure 97. 4-Wire Drive, AC-Excitation Example The recommended sequence AC-excitation configuration is as follows: 1. Stop conversions by taking the START pin low, or by control of conversions in software mode; send the STOP command 2. Program the input and reference MUX, gain, data rata, filter mode and other configurations as needed 3. Program the 2-wire or 4-wire AC-excitation mode 4. Program the 2 GPIOs or 4 GPIOs internal connection to the analog input pins 5. Program the 2 GPIOs or 4 GPIOs as outputs to enable drive signals at the analog input pins. Start the conversions. Adjust the time delay parameter as necessary based on the time constant of the input and reference filters. 74 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Application Information (continued) 10.1.6 Serial Interface and Digital Connections Figure 98 shows an example of the digital connections from a host µC to the ADC. Not all I/O connections are necessary for basic ADC operation; see the Unused Inputs and Outputs section. Impedance-matching resistors in series with the I/O PCB traces help reduce overshoot and ringing, and is particularly helpful over long trace runs. Optional Clock Source ADC 47 CLKIN Host µC 47 PWDN 47 RESET 47 START Port Pin Port Pin Port Pin Port Pin (CS) 47 CS 47 SCLK 47 DIN SCLK MOSI 47 MISO 47 ,54; DOUT /DRDY DRDY Figure 98. Serial Interface and Digital I/O Connections Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 75 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 10.2 Typical Application Figure 99 shows a fault-protected, 3-wire RTD application with hardware-based, lead-wire compensation. Two current sources are used together to compensate the RTD lead wire resistance. One current source (IDAC1) provides excitation to the RTD element through RLEAD1. The reference voltage of the ADC is derived directly from this current by resistor RREF. The second current source cancels lead-wire resistance by generating a voltage drop on lead-wire resistance RLEAD2 equal to the voltage drop of RLEAD1. Because the RRTD signal voltage is measured differentially via inputs AIN2 and AIN3, the voltages across the lead wire resistance cancel. Resistor RBIAS level-shifts the RTD signal voltage to within the ADC input range. The current sources route to the RTD element through low VF diodes to provide input fault protection. 5V 3.3 V 1 µF 0.1 PF PF DVDD AVDD IDAC1 IIDAC1 AINCOM 1 µF BYPASS AVDD CAPP (IDAC1) ADS1260 ADS1261 500 A 4.7 nF C0G CAPN CCM4 RF4 AIN0 RREF (REFP0) Internal Reference Reference Mux CDIF2 RF3 AIN1 REFOUT (REFN0) PF CCM3 Ref Mon Buf 3-Wire RTD RLEAD1 START CCM2 RF2 RESET AIN2 RRTD RLEAD2 PWDN Input Mux CDIF1 RF1 PGA ADC Digital Filter AIN3 Serial Interface and Control CS DIN DOUT/DRDY SCLK CCM1 DRDY Signal Mon IIDAC2 AIN4 IDAC2 (IDAC2) AVDD Internal Oscillator 500 A AVSS RLEAD3 Clock Mux CLKIN DGND IIDAC1 + IIDAC2 RBIAS Figure 99. RTD Element With 3-Wire Lead Resistance Compensation 10.2.1 Design Requirements The key considerations in the design of a 3-wire RTD circuit are the accuracy, stability and noise of the measurement, accuracy of the lead-wire compensation and self-heating of the sensor. Stability of the measurement is determined by the offset and gain drift of the ADC and by the drift of the external reference resistor. Measurement noise is determined by the ADC sample rate and by the digital filter settings. These parameters are not summarized here. Table 45 summarizes the basic design goals for a 3-wire Pt100 RTD. Table 45. Design Goals DESIGN PARAMETER 76 VALUE RTD sensor type 3-wire Pt100 RTD resistance range 20 Ω to 400 Ω RTD lead resistance range 0 Ω to 10 Ω RTD self heating < 1 mW Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 Table 46 summarize the parameters of the detailed design procedure that follows. Table 46. Design Parameters DESIGN PARAMETER DESIGN VALUE IIDAC IDAC current 500 µA PRTD RTD power dissipation 0.1 mW VRTD RTD input voltage 0.20 V Gain ADC gain VREF Reference voltage (design target allows for 10% overrange) 1.76 V RREF Reference resistor (senses the IDAC current to generate VREF) 3.52 kΩ RBIAS Bias resistor (provides the RTD level-shift voltage) 1.10 kΩ VRTDN RTD negative input voltage 1.1 V VRTDP RTD positive input voltage 1.31 V VIDAC1 IDAC1 loop voltage 3.37 V 8 10.2.2 Detailed Design Procedure IDAC1 current flows through reference resistor, RREF, which generates the ADC reference voltage, VREF = IIDAC1 · RREF. IDAC1 current also flows through the RTD element. Since the same current flows through RREF and the RTD element, the RTD measurement is ratiometric, which means the drift and error of the current source are cancelled. Therefore, the measurement accuracy is solely dependent on the tolerance of RREF and on ADC gain and offset errors. The errors are calibrated by host software control using shorted-input calibration and using a 400 Ω precision resistor for full-scale calibration. The current of IDAC2 is programmed to the same value as IDAC1 and is connected to RLEAD2. IDAC2 generates an equal voltage drop across RLEAD1 and IDAC1. The accuracy of lead-wire compensation depends on the matching error between IDAC1 to IDAC2. Using RRTD = 400 Ω, IDAC current = 500 µA, and gain = 8, the minimum ADC reference voltage requirement calculates to 1.6 V. To provide 10% design margin, RREF calculates to 3.52 kΩ (1.76 V / 500 µA). 500 µA is selected to minimize heating of the sensor. Resistor RBIAS level-shifts the RTD voltage to meet the input range requirement of the ADC. This voltage is VRTDN and the low limit is calculated by Equation 8. The VRTDN low limit is 1 V. AVSS + 0.3 V + VRTD · (Gain – 1) / 2 ≤ VRTDN (8) Using 10% design margin, RBIAS calculates to 1.1 kΩ = 1.1 V / (2 · 500 µA). The next step is to verify the positive RTD voltage (VRTDP) does not exceed the maximum input range, as shown in Equation 9: Maximum VRTDP ≤ AVDD – 0.3 V – VRTD · (Gain – 1) / 2 (9) Evaluation of the equation results in the VRTDP high limit = 3.75 V. Calculate the actual VRTDP input voltage by Equation 10: Actual VRTDP = VRTDN + IIDAC1 · ( RRTD + 2 · RLEAD) = 1.1 V + 500 µA · (400 Ω + 20 Ω) = 1.31 V (10) VRTDN = 1.1 V and VRTDP = 1.31 V satisfy the negative and positive input voltage requirements of the ADC, respectively. Verify the burden voltage of current source IDAC1 is below the specified compliance range. The burden voltage is the sum of voltages in the IDAC1 loop as calculated by VRTDP+ (IDAC1 · RREF) + VD ( VD= external diode voltage). The result is 3.37 V, which meets the specified compliance voltage of the current source. External filter components RF1, RF2, CDIF1, CCM1, CCM2) and RF3, RF4, CDIF2, CCM3, and CCM4) filter the signal and reference inputs of the ADC. The filters remove both differential and common-mode noise. The input signal differential filter cutoff frequency as calculated by Equation 11: fDIF = 1 / [2π · RF1 + RF2) · RDIF1 + CM1|| CM2)] (11) The Input signal common-mode filter is calculated by Equation 12: fCM = 1 / (2π · RF1 · CM1) = 1 / (2π · RF2 · CM2) Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 (12) Submit Documentation Feedback 77 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Component mismatch in the common-mode filter converts common-mode noise into differential noise. Use a differential capacitor CDIF1 10× higher value than the common-mode capacitors, CCM1 and CCM2 to minimize the effects of mismatch. The recommended range of input resistors is 1 kΩ to 10 kΩ; increasing the resistance beyond 10 kΩ beyond can compromise noise and drift performance of the ADC. Use high-quality C0G ceramics or film-type capacitors. For consistent noise performance across the full RTD temperature range, match the corner frequencies of the input and reference filters. Detailed information is found in the RTD Ratiometric Measurements and Filtering Using the ADS1148 and ADS1248 Family of Devices application report. 10.2.3 Application Curves Figure 100 shows the resistance measurement results. The measurements are taken at TA = 25°C. The data are taken using a precision resistor simulator with a 3-wire connection in place of the RTD. A system offset calibration is performed using shorted inputs. A system gain calibration is performed using a 390-Ω precision resistor. The measurement data are in ohms and do not include the error of the RTD sensor. The measured resistance error is < ±0.02 Ω over the 20-Ω to 400-Ω range. Measurement Error (:) 0.1 0.05 0 -0.05 -0.1 0 50 100 150 200 250 300 350 400 RTD Value (:) Figure 100. 3-Wire RTD Example Measurement Results 78 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 10.3 Initialization Setup Figure 101 shows a general configuration and measurement procedure. Power On /* These pins must be high for operation Set RESET and PWDN high Y External clock? Apply clock to CLKIN /* ADC automatically detects external clock N N /* DRDY is held low at power-on until ready for communication DRDY pin high? Y Y START high? DRDY pulses at 20 Hz /* If START pin is low, conversions are stopped N Set START low or STOP command /* For simplicity, stop conversions before register configuration DRDY not pulsing /* Write register data, CRC verfication is optional Configure the ADC Verify registers /* Readback register data for verification Wait for reference voltage to settle /* The internal reference requires time to settle after power-on Set START pin high or START command /* Start or restart new ADC conversion N Hardware DRDY? Read STATUS register /* Read data at a rate faster than the data rate to avoid missed data Y N N DRDY bit asserted ? /* New data when DRDY bit =1 DRDY pin low ? Y Y Read Data N Change ADC settings ? Y Figure 101. ADC Configuration and Measurement Procedure Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 79 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com 11 Power Supply Recommendations The ADC requires an analog power supply (AVDD, AVSS) and digital power supply (DVDD). The analog power supply can be bipolar (AVDD = +2.5 V and AVSS = –2.5 V) or unipolar (AVDD = 5 V and AVSS = DGND). The digital supply range is 2.7 V to 5.25 V. DVDD powers the ADC core by use of an internal regulator. DVDD also sets the digital I/O voltage. Keep in mind that the GPIO I/O voltages are AVDD and AVSS. Voltage ripple produced by switch-mode power supplies may interfere with the ADC conversions. Use low-dropout regulators (LDOs) to reduce switch-mode power supply ripple. 11.1 Power-Supply Decoupling Good power-supply decoupling is important in order to achieve optimum performance. Power supplies must be decoupled close to the power supply pins using short, direct connections to ground. For the analog supply, place 0.1-µF and 10-µF capacitors between AVDD and AVSS and 0.1-µF capacitors from each supply to ground. Connect a 1-µF capacitor from DVDD to the ground plane. Connect a 1-µF capacitor from BYPASS to the ground plane. 11.2 Analog Power-Supply Clamp It is important to evaluate circumstances when an input signal is present with the ADC, both powered and unpowered. When the input signal exceeds the power-supply voltage, it is possible to backdrive the analog power-supply voltage with the input signal through a conduction path of the internal ESD diodes. Backdriving the ADC power supply can also occur when the power-supply is on. The backdriven current path is illustrated in Figure 102. Depending on how the power supply responds during a backdriven condition, it is possible to exceed the maximum rated ADC supply voltage. The ADC voltage must not be exceeded at all times. One solution is to clamp the analog supply to safe voltage using an external zener diode. ADC supply On or Off IFAULT +V +5 V Reg AVDD RLIMIT AINx Input Voltage + ± ESD Diode Optional 6-V Zener Diode ADC AINx IFAULT ESD Diode IFAULT AVSS Figure 102. Analog Power-Supply Clamp 11.3 Power-Supply Sequencing The power supplies can be sequenced in any order, but do not allow the analog or digital inputs to exceed the respective analog or digital power-supplies without external limits of the possible input fault currents. 80 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 12 Layout Good layout practices are crucial to realize the full-performance of the ADC. Poor grounding can quickly degrade the noise performance. The following layout guidelines help provide the best results. 12.1 Layout Guidelines For best performance, dedicate an entire PCB layer to a ground plane and do not route any other signal traces on this layer. However, depending on restrictions imposed by specific end equipment, a dedicated ground plane may not be practical. If ground plane separation is necessary, make a direct connection of the planes at the ADC. Do not connect individual ground planes at multiple locations because this configuration creates ground loops. Route digital traces away from the CAPP and CAPN pins, away from the REFOUT pin, and away from all analog inputs and associated components in order to minimize interference. Avoid long traces on DOUT/DRDY, because high capacitance on this pin can lead to increase of ADC noise levels. Use a series resistor or a buffer if long traces are used. The internal reference output return shares the same pin as the AVSS power supply. To minimize coupling between the power supply and reference-return trace, route the traces separately; ideally, as a star connection to the AVSS pin. Use C0G capacitors on the analog inputs and for the CAPP to CAPN capacitor. Use ceramic capacitors (for example, X7R grade) for the power supply decoupling capacitors. High-K capacitors (Y5V) are not recommended. The REFOUT pin requires a 10-µF capacitor and can be either ceramic or tantalum type. Place the required capacitors as close as possible to the device pins using short, direct traces. For optimum performance, use low-impedance connections on the ground-side connections of the bypass capacitors. When applying an external clock, be sure the clock is free of overshoot and glitches. A source-termination resistor placed at the clock buffer often helps reduce overshoot. Glitches present on the clock input can lead to noise within the conversion data. 12.2 Layout Example Figure 103 is an example layout of the ADS1261, requiring a minimum of three PCB layers. The example circuit is shown with single supply operation (AVSS = DGND). In this example, the inner layer is dedicated to the ground plane and the outer layers are used for signal and power traces. If a four-layer PCB is used, dedicate the additional inner layer as the power plane. In this example, the ADC is oriented in such a way to minimize crossover of the analog and digital signal traces. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 81 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com Layout Example (continued) ADC Clock Options: Option 1: To enable INTERNAL oscillator, tie CLKIN to GND C0G DVDD Supply (Differential Input Pair) Option 2: Connect EXTERNAL clock source to CLKIN AIN7 NC CLKIN DVDD 17 NC 18 NC 20 19 NC 21 AIN9 22 AIN8 23 C0G 24 1 µF (Leave NC pins floating) 25 1 µF 16 DGND 15 BYPASS 14 DOUT/ DRDY (Differential Input Pair) AIN6 26 AIN5 27 ADS1261 (Differential Input Pair) AIN4 28 13 DRDY AIN3 29 12 DIN C0G To Analog Circuitry (Differential Input Pair) Connect thermal pad to AVSS 11 SCLK 31 10 CS 32 9 START AIN2 30 AIN1 8 To MCU RESET 7 PWDN 5 6 REFOUT AVDD AVSS 4 3 CAPN 1 4.7 nF AINCOM C0G CAPP AIN0 2 (Differential Input Pair) C0G (0805 shown) (0805 shown) C0G 1 µF (0603 shown) (9-mil traces shown) 10 µF 10 µF AVDD Supply For Unipolar Supply, AVSS = GND Reference Output Figure 103. ADS1261 Layout Example 82 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 13 Device and Documentation Support 13.1 Documentation Support 13.1.1 Related Documentation For related documentation see the following: Texas Instruments, ADS1261 and ADS1235 Evaluation Module user's guide 13.2 Related Links The table below lists quick access links. Categories include technical documents, support and community resources, tools and software, and quick access to order now. Table 47. Related Links PARTS PRODUCT FOLDER ORDER NOW TECHNICAL DOCUMENTS TOOLS & SOFTWARE SUPPORT & COMMUNITY ADS1260 Click here Click here Click here Click here Click here ADS1261 Click here Click here Click here Click here Click here 13.3 Receiving Notification of Documentation Updates To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper right corner, click on Alert me to register and receive a weekly digest of any product information that has changed. For change details, review the revision history included in any revised document. 13.4 Community Resources The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of Use. TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help solve problems with fellow engineers. Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and contact information for technical support. 13.5 Trademarks E2E is a trademark of Texas Instruments. All other trademarks are the property of their respective owners. 13.6 Electrostatic Discharge Caution This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. 13.7 Glossary SLYZ022 — TI Glossary. This glossary lists and explains terms, acronyms, and definitions. 14 Mechanical, Packaging, and Orderable Information The following pages include mechanical packaging and orderable information. This information is the most current data available for the designated devices. This data is subject to change without notice and revision of this document. For browser-based versions of this data sheet, refer to the left-hand navigation. Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 83 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com PACKAGE OUTLINE RHB0032E VQFN - 1 mm max height SCALE 3.000 PLASTIC QUAD FLATPACK - NO LEAD 5.1 4.9 A B PIN 1 INDEX AREA 5.1 4.9 C 1 MAX SEATING PLANE 0.05 0.00 0.08 C 2X 3.5 (0.2) TYP 3.45 0.1 9 EXPOSED THERMAL PAD 16 28X 0.5 8 17 2X 3.5 SYMM 33 32X 24 1 PIN 1 ID (OPTIONAL) 32 0.3 0.2 0.1 0.05 C A B C 25 SYMM 0.5 32X 0.3 4223442/A 11/2016 NOTES: 1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing per ASME Y14.5M. 2. This drawing is subject to change without notice. 3. The package thermal pad must be soldered to the printed circuit board for thermal and mechanical performance. www.ti.com 84 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 ADS1260, ADS1261 www.ti.com SBAS760C – MARCH 2018 – REVISED JANUARY 2019 EXAMPLE BOARD LAYOUT RHB0032E VQFN - 1 mm max height PLASTIC QUAD FLATPACK - NO LEAD ( 3.45) SYMM 32 25 32X (0.6) 1 24 32X (0.25) (1.475) 28X (0.5) 33 SYMM (4.8) ( 0.2) TYP VIA 8 17 (R0.05) TYP 9 (1.475) 16 (4.8) LAND PATTERN EXAMPLE SCALE:18X 0.07 MIN ALL AROUND 0.07 MAX ALL AROUND SOLDER MASK OPENING METAL SOLDER MASK OPENING METAL UNDER SOLDER MASK NON SOLDER MASK DEFINED (PREFERRED) SOLDER MASK DEFINED SOLDER MASK DETAILS 4223442/A 11/2016 NOTES: (continued) 4. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature number SLUA271 (www.ti.com/lit/slua271). 5. Vias are optional depending on application, refer to device data sheet. If any vias are implemented, refer to their locations shown on this view. It is recommended that vias under paste be filled, plugged or tented. www.ti.com Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 Submit Documentation Feedback 85 ADS1260, ADS1261 SBAS760C – MARCH 2018 – REVISED JANUARY 2019 www.ti.com EXAMPLE STENCIL DESIGN RHB0032E VQFN - 1 mm max height PLASTIC QUAD FLATPACK - NO LEAD 4X ( 1.49) (0.845) (R0.05) TYP 32 25 32X (0.6) 1 24 32X (0.25) 28X (0.5) (0.845) SYMM 33 (4.8) 17 8 METAL TYP 16 9 SYMM (4.8) SOLDER PASTE EXAMPLE BASED ON 0.125 mm THICK STENCIL EXPOSED PAD 33: 75% PRINTED SOLDER COVERAGE BY AREA UNDER PACKAGE SCALE:20X 4223442/A 11/2016 NOTES: (continued) 6. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate design recommendations. www.ti.com 86 Submit Documentation Feedback Copyright © 2018–2019, Texas Instruments Incorporated Product Folder Links: ADS1260 ADS1261 PACKAGE OPTION ADDENDUM www.ti.com 10-Dec-2020 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan (2) Lead finish/ Ball material MSL Peak Temp Op Temp (°C) Device Marking (3) (4/5) (6) ADS1260BIRHBR ACTIVE VQFN RHB 32 3000 RoHS & Green NIPDAU Level-3-260C-168 HR -40 to 125 ADS 1260B ADS1260BIRHBT ACTIVE VQFN RHB 32 250 RoHS & Green NIPDAU Level-3-260C-168 HR -40 to 125 ADS 1260B ADS1261BIRHBR ACTIVE VQFN RHB 32 3000 RoHS & Green NIPDAU Level-3-260C-168 HR -40 to 125 ADS 1261B ADS1261BIRHBT ACTIVE VQFN RHB 32 250 RoHS & Green NIPDAU Level-3-260C-168 HR -40 to 125 ADS 1261B ADS1261IRHBR ACTIVE VQFN RHB 32 3000 RoHS & Green NIPDAU Level-3-260C-168 HR -40 to 125 ADS 1261 ADS1261IRHBT ACTIVE VQFN RHB 32 250 RoHS & Green NIPDAU Level-3-260C-168 HR -40 to 125 ADS 1261 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of