ADS1211U

® ADS 121 1 ADS 1210 ADS 121 0 ADS1210 ADS1211 ADS 1211 ADS 121 1 24-Bit ANALOG-TO-DIGITAL CONVERTER FEATURES q DELTA-SIGMA A/D CONVERTER q 23 BITS EFFECTIVE RESOLUTION AT 10Hz AND 20 BITS AT 1000Hz q DIFFERENTIAL INPUTS q PROGRAMMABLE GAIN AMPLIFIER q FLEXIBLE SPI COMPATIBLE SSI INTERFACE WITH 2-WIRE MODE q PROGRAMMABLE CUT-OFF FREQUENCY UP TO 15.6kHz q INTERNAL/EXTERNAL REFERENCE q ON CHIP SELF-CALIBRATION q ADS1211 INCLUDES 4 CHANNEL MUX DESCRIPTION The ADS1210 and ADS1211 are precision, wide dynamic range, delta-sigma analog-to-digital converters with 24-bit resolution operating from a single +5V supply. The differential inputs are ideal for direct connection to transducers or low level voltage signals. The delta-sigma architecture is used for wide dynamic range and to guarantee 22 bits of no missing code performance. An effective resolution of 23 bits is achieved through the use of a very low-noise input amplifier at conversion rates up to 10Hz. Effective resolutions of 20 bits can be maintained up to a sample rate of 1kHz through the use of the unique Turbo modulator mode of operation. The dynamic range of the converters is further increased by providing a low-noise programmable gain amplifier with a gain range of 1 to 16 in binary steps. The ADS1210 and ADS1211 are designed for high resolution measurement applications in smart transmitters, industrial process control, weigh scales, chromatography and portable instrumentation. Both converters include a flexible synchronous serial interface which is SPI compatible and also offers a two-wire control mode for low cost isolation. The ADS1210 is a single channel converter and is offered in both 18-pin DIP and 18-lead SOIC packages. The ADS1211 includes a 4 channel input multiplexer and is available in 24-pin DIP, 24-lead SOIC, and 28-lead SSOP packages. VBIAS XIN XOUT APPLICATIONS q q q q q q q INDUSTRIAL PROCESS CONTROL INSTRUMENTATION BLOOD ANALYSIS SMART TRANSMITTERS PORTABLE INSTRUMENTS WEIGH SCALES PRESSURE TRANSDUCERS AGND AVDD REFOUT REFIN AIN1P AIN1N AIN2P AIN2N AIN3P AIN3N AIN4P AIN4N MUX AINP +2.5V Reference +3.3V Bias Generator Clock Generator DGND DVDD Micro Controller Second-Order ∆∑ Modulator Third-Order Digital Filter Instruction Register Command Register Data Output Register Offset Register Full-Scale Register SCLK SDIO SDOUT PGA AINN Modulator Control Serial Interface ADS1211 Only ADS1210/11 DSYNC CS MODE DRDY International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 Twx: 910-952-1111 • Internet: http://www.burr-brown.com/ • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 ® © 1996 Burr-Brown Corporation PDS-1284E 1 ADS1210, 1211 Printed in U.S.A. May, 2000 SPECIFICATIONS All specifications TMIN to TMAX, AVDD = DVDD = +5V, fXIN = 10MHz, programmable gain amplifier setting of 1, Turbo Mode Rate of 1, REFOUT disabled,VBIAS disabled, and external 2.5V reference, unless otherwise specified. ADS1210U, P/ADS1211U, P, E PARAMETER ANALOG INPUT Input Voltage Range(1) Input Impedance Programmable Gain Amplifier Input Capacitance Input Leakage Current SYSTEMS PERFORMANCE Resolution No Missing Codes Integral Linearity fDATA Unipolar Offset Error(4) Unipolar Offset Drift(6) Gain Error(4) Gain Error Drift(6) Common-Mode Rejection(9) With VBIAS(2) G = Gain, TMR = Turbo Mode Rate User Programmable: 1, 2, 4, 8, or 16 At +25°C At TMIN to TMAX CONDITIONS MIN TYP MAX UNITS 0 –10 4/(G • TMR)(3) 1 8 5 +5 +10 16 50 1 V V MΩ pF pA nA Bits Bits %FSR %FSR µV/°C µV/°C dB dB dB dB dB dB dB 24 fDATA = 60Hz fDATA = 60Hz = 1000Hz, TMR of 16 22 ±0.0015 ±0.0015 See Note 5 1 See Note 5 1 115 115 Normal-Mode Rejection Output Noise Power Supply Rejection VOLTAGE REFERENCE Internal Reference (REFOUT) Drift Noise Load Current Output Impedance External Reference (REFIN) Load Current VBIAS Output Drift Load Current DIGITAL INPUT/OUTPUT Logic Family Logic Level: (all except XIN) VIH VIL VOH VOL XIN Input Levels: VIH VIL XIN Frequency Range (fXIN) Output Data Rate (fDATA) Data Format SYSTEM CALIBRATION Offset and Full-Scale Limits VFS – | VOS | At DC, +25°C At DC, TMIN to TMAX 50Hz, fDATA = 50Hz(7) 60Hz, fDATA = 60Hz(7) 50Hz, fDATA = 50Hz(7) 60Hz, fDATA = 60Hz(7) DC, 50Hz, and 60Hz 100 90 160 160 100 100 65 2.4 See Typical Performance Curves 2.5 25 50 2 2.6 Source or Sink 2.0 Using Internal Reference Source or Sink TTL Compatible CMOS IIH = +5µA IIL = +5µA = 2 TTL Loads = 2 TTL Loads 2.0 –0.3 2.4 3.5 –0.3 0.5 2.4 0.12 Two’s Complement or Offset Binary 0.7 • (2 • REFIN)/G 3.15 3.3 50 1 3.0 2.5 3.45 10mA V ppm/°C µVp-p mA Ω V µA V ppm/°C DVDD +0.3 0.8 0.4 DVDD +0.3 0.8 10 15,625 781 IOH IOL User Programmable fXIN = 500kHz User Programmable V V V V V V MHz Hz Hz VFS = Full-Scale Differential Voltage(8) VOS = Offset Differential Voltage(8) 1.3 • (2 • REFIN)/G The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. ® ADS1210, 1211 2 SPECIFICATIONS (CONT) All specifications TMIN to TMAX, AVDD = DVDD = +5V, fXIN = 10MHz, programmable gain amplifier setting of 1, Turbo Mode Rate of 1, REFOUT disabled,VBIAS disabled, and external 2.5V reference, unless otherwise specified. ADS1210U, P/ADS1211U, P, E PARAMETER POWER SUPPLY REQUIREMENTS Power Supply Voltage Power Supply Current: Analog Current Digital Current Additional Analog Current with REFOUT Enabled VBIAS Enabled Power Dissipation CONDITIONS MIN 4.75 2 3.5 1.6 1 26 37 17 27 11 –40 –60 TYP MAX 5.25 UNITS V mA mA mA mA mW mW mW mW mW °C °C No Load TMR of 16 fXIN = 2.5MHz = 2.5MHz, TMR of 16 Sleep Mode 40 60 fXIN TEMPERATURE RANGE Specified Storage +85 +125 NOTES: (1) In order to achieve the converter’s full-scale range, the input must be fully differential (AINN = 2 • REFIN – AINP). If the input is single-ended (AINN or AINP is fixed), then the full scale range is one-half that of the differential range. (2) This range is set with external resistors and VBIAS (as described in the text). Other ranges are possible. (3) Input impedance is higher with lower fXIN. (4) Applies after calibration. (5) After system calibration, these errors will be of the order of the effective resolution of the converter. Refer to the Typical Performance Curves which apply to the desired mode of operation. (6) Recalibration can remove these errors. (7) The specification also applies at fDATA /i, where i is 2, 3, 4, etc. (8) Voltages at the analog inputs must remain within AGND to AVDD. (9) The commonmode rejection test is performed with a 100mV differential input. ABSOLUTE MAXIMUM RATINGS Analog Input: Current ................................................ ±100mA, Momentary ±10mA, Continuous Voltage ................................... AGND –0.3V to AVDD +0.3V AVDD to DVDD ........................................................................... –0.3V to 6V AVDD to AGND ......................................................................... –0.3V to 6V DVDD to DGND ......................................................................... –0.3V to 6V AGND to DGND ................................................................................ ±0.3V REFIN Voltage to AGND ............................................ –0.3V to AVDD +0.3V Digital Input Voltage to DGND .................................. –0.3V to DVDD +0.3V Digital Output Voltage to DGND ............................... –0.3V to DVDD +0.3V Lead Temperature (soldering, 10s) .............................................. +300°C Power Dissipation (Any package) .................................................. 500mW PACKAGE/ORDERING INFORMATION PACKAGE DRAWING NUMBER(1) 218 219 243 239 324 TEMPERATURE RANGE –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C PRODUCT ADS1210P ADS1210U ADS1211P ADS1211U ADS1211E PACKAGE 18-Pin Plastic DIP 18-Lead SOIC 24-Pin Plastic DIP 24-Lead SOIC 28-Lead SSOP NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Burr-Brown recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. Electrostatic discharge can cause damage ranging from performance degradation to complete device failure. BurrBrown Corporation recommends that all integrated circuits be handled and stored using appropriate ESD protection methods. ® 3 ADS1210, 1211 ADS1210 SIMPLIFIED BLOCK DIAGRAM AGND 3 AVDD 16 REF OUT 17 +2.5V Reference REF IN 18 VBIAS 4 +3.3V Bias Generator XIN 7 XOUT 8 Clock Generator 9 10 1 2 PGA Micro Controller Second-Order ∆Σ Modulator Third-Order Digital Filter Instruction Register Command Register Data Output Register Offset Register Full-Scale Register 11 Modulator Control Serial Interface 6 DSYNC 5 CS 15 MODE 14 DRDY 12 13 SCLK SDIO SDOUT DGND DVDD AINP AINN ADS1210 PIN CONFIGURATION TOP VIEW DIP/SOIC ADS1210 PIN DEFINITIONS PIN NO 1 2 3 NAME AINP AINN AGND VBIAS CS DSYNC XIN XOUT DGND DVDD SCLK SDIO SDOUT DRDY MODE AVDD REFOUT REFIN DESCRIPTION Noninverting Input. Inverting Input. Analog Ground. Bias Voltage Output, +3.3V nominal. Chip Select Input. Control Input to Synchronize Serial Output Data. System Clock Input. System Clock Output (for Crystal or Resonator). Digital Ground. Digital Supply, +5V nominal. Clock Input/Output for serial data transfer. Serial Data Input (can also function as Serial Data Output). Serial Data Output. Data Ready. SCLK Control Input (Master = 1, Slave = 0). Analog Supply, +5V nominal. Reference Output, +2.5V nominal. Reference Input. AINP AINN AGND VBIAS CS DSYNC XIN XOUT DGND 1 2 3 4 5 6 7 8 9 ADS1210 18 REFIN 17 REFOUT 16 AVDD 15 MODE 14 DRDY 13 SDOUT 12 SDIO 4 5 6 7 8 9 10 11 12 13 11 SCLK 10 DVDD 14 15 16 17 18 ® ADS1210, 1211 4 ADS1211 SIMPLIFIED BLOCK DIAGRAM AGND 6 AVDD 19 REFOUT 20 +2.5V Reference REFIN 21 VBIAS 7 +3.3V Bias Generator XIN 10 XOUT 11 Clock Generator 12 13 Micro Controller MUX Second-Order ∆∑ Modulator Third-Order Digital Filter Instruction Register Command Register Data Output Register Offset Register Full-Scale Register 14 15 16 17 DRDY SCLK SDIO SDOUT DGND DVDD AIN1P AIN1N AIN2P AIN2N AIN3P AIN3N AIN4P AIN4N 4 5 2 3 24 1 22 23 PGA Modulator Control Serial Interface 9 DSYNC 8 CS 18 MODE ADS1211P AND ADS1211U PIN CONFIGURATION TOP VIEW DIP/SOIC ADS1211P AND ADS1211U PIN DEFINITIONS PIN NO 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 NAME AIN3N AIN2P AIN2N AIN1P AIN1N AGND VBIAS CS DSYNC XIN XOUT DGND DVDD SCLK SDIO SDOUT DRDY MODE AVDD REFOUT REFIN AIN4P AIN4N AIN3P DESCRIPTION Inverting Input Channel 3. Noninverting Input Channel 2. Inverting Input Channel 2. Noninverting Input Channel 1. Inverting Input Channel 1. Analog Ground. Bias Voltage Output, +3.3V nominal. Chip Select Input. Control Input to Synchronize Serial Output Data. System Clock Input. System Clock Output (for Crystal or Resonator). Digital Ground. Digital Supply, +5V nominal. Clock Input/Output for serial data transfer. Serial Data Input (can also function as Serial Data Output). Serial Data Output. Data Ready. SCLK Control Input (Master = 1, Slave = 0). Analog Supply, +5V nominal. Reference Output: +2.5V nominal. Reference Input. Noninverting Input Channel 4. Inverting Input Channel 4. Noninverting Input Channel 3. AIN3N AIN2P AIN2N AIN1P AIN1N AGND VBIAS CS DSYNC 1 2 3 4 5 6 7 8 9 ADS1211P ADS1211U 24 AIN3P 23 AIN4N 22 AIN4P 21 REFIN 20 REFOUT 19 AVDD 18 MODE 17 DRDY 16 SDOUT 15 SDIO 14 SCLK 13 DVDD XIN 10 XOUT 11 DGND 12 ® 5 ADS1210, 1211 ADS1211E PIN CONFIGURATION TOP VIEW SSOP ADS1211E PIN DEFINITIONS PIN NO 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 NAME AIN3N AIN2P AIN2N AIN1P AIN1N AGND VBIAS NIC NIC CS DSYNC XIN XOUT DGND DVDD SCLK SDIO SDOUT DRDY NIC NIC MODE AVDD REFOUT REFIN AIN4P AIN4N AIN3P DESCRIPTION Inverting Input Channel 3. Noninverting Input Channel 2. Inverting Input Channel 2. Noninverting Input Channel 1. Inverting Input Channel 1. Analog Ground. Bias Voltage Output, +3.3V nominal. Not Internally Connected. Not Internally Connected. Chip Select Input. Control Input to Synchronize Serial Output Data. System Clock Input. System Clock Output (for Crystal or Resonator). Digital Ground. Digital Supply, +5V nominal. Clock Input/Output for serial data transfer. Serial Data Input (can also function as Serial Data Output). Serial Data Output. Data Ready. Not Internally Connected. Not Internally Connected. SCLK Control Input (Master = 1, Slave = 0). Analog Supply, +5V nominal. Reference Output: +2.5V nominal. Reference Input. Noninverting Input Channel 4. Inverting Input Channel 4. Noninverting Input Channel 3. AIN3N AIN2P AIN2N AIN1P AIN1N AGND VBIAS NIC NIC 1 2 3 4 5 6 7 8 9 ADS1211E 28 AIN3P 27 AIN4N 26 AIN4P 25 REFIN 24 REFOUT 23 AVDD 22 MODE 21 NIC 20 NIC 19 DRDY 18 SDOUT 17 SDIO 16 SCLK 15 DVDD CS 10 DSYNC 11 XIN 12 XOUT 13 DGND 14 ® ADS1210, 1211 6 TYPICAL PERFORMANCE CURVES At TA = +25°C, AVDD = DVDD = +5V, fXIN = 10MHz, programmable gain amplifier setting of 1, Turbo Mode Rate of one, REFOUT disabled, VBIAS disabled, and external 2.5V reference, unless otherwise noted. EFFECTIVE RESOLUTION vs DATA RATE (1MHz Clock) 24 24 EFFECTIVE RESOLUTION vs DATA RATE (2.5MHz Clock) Effective Resolution in Bits (rms) 22 20 18 Turbo 1 16 Turbo 2 14 Turbo 4 12 1 10 Data Rate (Hz) 100 1k Turbo 8 Effective Resolution in Bits (rms) Turbo 16 Turbo 16 22 20 18 16 14 Turbo 4 12 1 10 Data Rate (Hz) 100 1k Turbo 1 Turbo 8 Turbo 2 EFFECTIVE RESOLUTION vs DATA RATE (5MHz Clock) 24 24 EFFECTIVE RESOLUTION vs DATA RATE (10MHz Clock) Effective Resolution in Bits (rms) 22 Turbo 8 20 Turbo 1 18 Turbo 2 16 Turbo 4 14 12 10 100 Data Rate (Hz) 1k Effective Resolution in Bits (rms) Turbo 16 Turbo 8 22 20 18 16 14 12 10 100 Data Rate (Hz) Turbo 4 Turbo 16 Turbo 1 Turbo 2 1k EFFECTIVE RESOLUTION vs DATA RATE 24 Effective Resolution in Bits (rms) 2.5 RMS NOISE vs INPUT VOLTAGE LEVEL (60Hz Data Rate) 22 20 18 16 14 12 10 PGA 1 PGA 2 PGA 4 RMS Noise (ppm) 2.0 PGA 16 PGA 8 1.5 1.0 10 100 Data Rate (Hz) 1k 0.5 –5.0 –4.0 –3.0 –2.0 –1.0 0 1.0 2.0 3.0 4.0 5.0 Analog Input Differential Voltage (V) ® 7 ADS1210, 1211 TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, AVDD = DVDD = +5V, fXIN = 10MHz, programmable gain amplifier setting of 1, Turbo Mode Rate of 1, REFOUT disabled, VBIAS disabled, and external 2.5V reference, unless otherwise noted. POWER DISSIPATION vs TURBO MODE RATE (REFOUT Enabled) 50.0 40.0 POWER DISSIPATION vs TURBO MODE RATE (External Reference; REFOUT) Power Dissipation (mW) 40.0 10MHz 30.0 5MHz 2.5MHz 1MHz 20.0 1 2 4 Turbo Mode Rate 8 16 Power Dissipation (mW) 30.0 10MHz 5MHz 20.0 2.5MHz 1MHz 10.0 1 2 4 Turbo Mode Rate 8 16 PSRR vs FREQUENCY 85.0 120.0 CMRR vs FREQUENCY 80.0 CMRR (dB) PSRR (dB) 75.0 115.0 70.0 65.0 0.1 1 10 100 Frequency (Hz) 1k 10k 100k 110.0 0.1 1 10 Frequency (Hz) 100 1k LINEARITY vs TEMPERATURE (60Hz Data Rate) 8 –40°C –5°C +25°C +55°C +85°C Integral Nonlinearity (ppm) 6 4 2 0 –2 –4 –6 –5 –4 –3 –2 –1 0 1 2 3 4 5 Analog Input Differential Voltage (V) ® ADS1210, 1211 8 THEORY OF OPERATION The ADS1210 and ADS1211 are precision, high dynamic range, self-calibrating, 24-bit, delta-sigma A/D converters capable of achieving very high resolution digital results. Each contains a programmable gain amplifier (PGA); a second-order delta-sigma modulator; a programmable digital filter; a microcontroller including the Instruction, Command and Calibration registers; a serial interface; a clock generator circuit; and an internal 2.5V reference. The ADS1211 includes a 4-channel input multiplexer. In order to provide low system noise, common-mode rejection of 115dB and excellent power supply rejection, the design topology is based on a fully differential switched capacitor architecture. Turbo Mode, a unique feature of the ADS1210/11, can be used to boost the sampling rate of the input capacitor, which is normally 19.5kHz with a 10MHz clock. By programming the Command Register, the sampling rate can be increased to 39kHz, 78kHz, 156kHz, or 312kHz. Each increase in sample rate results in an increase in performance when maintaining the same output data rate. The programmable gain amplifier (PGA) of the ADS1210/ 11 can be set to a gain of 1, 2, 4, 8 or 16—substantially increasing the dynamic range of the converter and simplifying the interface to the more common transducers (see Table I). This gain is implemented by increasing the number of samples taken by the input capacitor from 19.5kHz for a gain of 1 to 312kHz for a gain of 16. Since the Turbo Mode and PGA functions are both implemented by varying the sampling frequency of the input capacitor, the combination of PGA gain and Turbo Mode Rate is limited to 16 (see Table II). For example, when using a Turbo Mode Rate of 8 (156kHz at 10MHz), the maximum PGA gain setting is 2. ANALOG INPUT(1) FULLSCALE RANGE (V) 10 5 2.5 1.25 0.625 EXAMPLE VOLTAGE RANGE(3) (V) 0 1.25 1.88 2.19 2.34 to to to to to 5 3.75 3.13 2.81 2.66 ANALOG INPUT UTILIZING VBIAS(1,2) FULLSCALE RANGE (V) 40 20 10 5 2.5 EXAMPLE VOLTAGE RANGE(3) (V) ±10 ±5 ±2.5 ±1.25 ±0.625 The output data rate of the ADS1210/11 can be varied from a few hertz to as much as 15,625kHz, trading off lower resolution results for higher data rates. In addition, the data rate determines the first null of the digital filter and sets the –3dB point of the input bandwidth (see the Digital Filter section). Changing the data rate of the ADS1210/11 does not result in a change in the sampling rate of the input capacitor. The data rate effectively sets the number of samples which are used by the digital filter to obtain each conversion result. A lower data rate results in higher resolution, lower input bandwidth, and different notch frequencies than a higher data rate. It does not result in any change in input impedance or modulator frequency, or any appreciable change in power consumption. The ADS1210/11 also includes complete on-board calibration that can correct for internal offset and gain errors or limited external system errors. Internal calibration can be run when needed, or automatically and continuously in the background. System calibration can be run as needed and the appropriate input voltages must be provided to the ADS1210/ 11. For this reason, there is no continuous System Calibration Mode. The calibration registers are fully readable and writable. This feature allows for switching between various configurations—different data rates, Turbo Mode Rates, and gain settings—without re-calibrating. The various settings, rates, modes, and registers of the ADS1210/11 are read or written via a synchronous serial interface. This interface can operate in either a self-clocked mode (Master Mode) or an externally clocked mode (Slave Mode). In the Master Mode, the serial clock (SCLK) frequency is one-half of the ADS1210/11 XIN clock frequency. This is an important consideration for many systems and may determine the maximum ADS1210/11 clock that can be used. The high resolution and flexibility of the ADS1210/11 allow these converters to fill a wide variety of A/D conversion tasks. In order to ensure that a particular configuration will meet the design goals, there are several important items which must be considered. These include (but are certainly not limited to) the needed resolution, required linearity, desired input bandwidth, power consumption goal, and sensor output voltage. The remainder of this data sheet discusses the operation of the ADS1210/11 in detail. In order to allow for easier comparison of different configurations, “effective resolution” is used as the figure of merit for most tables and graphs. For example, Table III shows a comparison between data rate (and –3dB input bandwidth) versus PGA setting at a Turbo Mode Rate of 1 and a clock rate of 10MHz. See the Definition of Terms section for a definition of effective resolution. GAIN SETTING 1 2 4 8 16 NOTE: (1) With a 2.5V reference, such as the internal reference. (2) This example utilizes the circuit in Figure 12. Other input ranges are possible. (3) The ADS1210/11 allows common-mode voltage as long as the absolute input voltage on AINP or AINN does not go below AGND or above AVDD. TABLE I. Full-Scale Range vs PGA Setting. TURBO MODE RATE 1 2 4 8 16 AVAILABLE PGA SETTINGS 1, 2, 4, 8, 16 1, 2, 4, 8 1, 2, 4 1, 2 1 TABLE II. Available PGA Settings vs Turbo Mode Rate. ® 9 ADS1210, 1211 DATA RATE (HZ) 10 25 30 50 60 100 250 500 1000 -3DB FREQUENCY (HZ) 2.62 6.55 7.86 13.1 15.7 26.2 65.5 131 262 EFFECTIVE RESOLUTION (BITS RMS) G=1 21.5 20.5 20.5 20.0 19.5 18.0 15.0 12.5 10.0 G=2 21.0 20.5 20.5 20.0 19.5 18.0 15.0 12.5 10.5 G=4 21.0 20.5 20.5 20.0 19.5 18.0 15.0 12.5 10.0 G=8 21.0 20.0 20.0 19.5 19.0 18.0 15.0 12.5 10.0 G = 16 20.0 19.5 19.5 19.0 19.0 18.0 15.0 12.5 10.0 For example, when the converter is configured with a 2.5V reference and placed in a gain setting of 2, the typical input voltage range is 1.25V to 3.75V. However, an input range of 0V to 2.5V or 2.5V to 5V would also cover the converter’s full-scale range. Voltage Span—This is simply the magnitude of the typical analog input voltage range. For example, when the converter is configured with a 2.5V reference and placed in a gain setting of 2, the input voltage span is 2.5V. Least Significant Bit (LSB) Weight—This is the theoretical amount of voltage that the differential voltage at the analog input would have to change in order to observe a change in the output data of one least significant bit. It is computed as follows: LSB Weight = Full−Scale Range 2N TABLE III. Effective Resolution vs Data Rate and Gain Setting. (Turbo Mode Rate of 1 and a 10MHz clock.) DEFINITION OF TERMS An attempt has been made to be consistent with the terminology used in this data sheet. In that regard, the definition of each term is given as follows: Analog Input Differential Voltage—For an analog signal that is fully differential, the voltage range can be compared to that of an instrumentation amplifier. For example, if both analog inputs of the ADS1210 are at 2.5V, then the differential voltage is 0V. If one is at 0V and the other at 5V, then the differential voltage magnitude is 5V. But, this is the case regardless of which input is at 0V and which is at 5V, while the digital output result is quite different. The analog input differential voltage is given by the following equation: AINP – AINN. Thus, a positive digital output is produced whenever the analog input differential voltage is positive, while a negative digital output is produced whenever the differential is negative. For example, when the converter is configured with a 2.5V reference and placed in a gain setting of 2, the positive fullscale output is produced when the analog input differential is 2.5V. The negative full-scale output is produced when the differential is –2.5V. In each case, the actual input voltages must remain within the AGND to AVDD range (see Table I). Actual Analog Input Voltage—The voltage at any one analog input relative to AGND. Full-Scale Range (FSR)—As with most A/D converters, the full-scale range of the ADS1210/11 is defined as the “input” which produces the positive full-scale digital output minus the “input” which produces the negative full-scale digital output. For example, when the converter is configured with a 2.5V reference and is placed in a gain setting of 2, the full-scale range is: [2.5V (positive full scale) minus –2.5V (negative full scale)] = 5V. Typical Analog Input Voltage Range—This term describes the actual voltage range of the analog inputs which will cover the converter’s full-scale range, assuming that each input has a common-mode voltage that is greater than REFIN/PGA and smaller than (AVDD – REFIN/PGA). where N is the number of bits in the digital output. Effective Resolution—The effective resolution of the ADS1210/11 in a particular configuration can be expressed in two different units: bits rms (referenced to output) and microvolts rms (referenced to input). Computed directly from the converter’s output data, each is a statistical calculation based on a given number of results. Knowing one, the other can be computed as follows:   10 V     PGA   20 • log   − 1. 76  ER in Vrms    ER in bits rms = 6. 02  10 V   PGA  ER in Vrms =  6. 02 • ER in bits rms + 1. 76    20 10 The 10V figure in each calculation represents the full-scale range of the ADS1210/11 in a gain setting of 1. This means that both units are absolute expressions of resolution—the performance in different configurations can be directly compared regardless of the units. Comparing the resolution of different gain settings expressed in bits rms requires accounting for the PGA setting. Main Controller— A generic term for the external microcontroller, microprocessor, or digital signal processor which is controlling the operation of the ADS1210/11 and receiving the output data. ® ADS1210, 1211 10 fXIN—The frequency of the crystal oscillator or CMOS compatible input signal at the XIN input of the ADS1210/11. fMOD—The frequency or speed at which the modulator of the ADS1210/11 is running, given by the following equation: Gain (dB) NORMALIZED DIGITAL FILTER RESPONSE 0 –20 –40 –60 –80 –100 –120 –140 –160 0 1 2 3 Frequency (Hz) 4 5 6 f MOD = f XIN • Turbo Mode 512 fSAMP—The frequency or switching speed of the input sampling capacitor. The value is given by the following equation: f SAMP = f XIN • Turbo Mode • Gain Setting 512 fDATA, tDATA—The frequency of the digital output data produced by the ADS1210/11 or the inverse of this (the period), respectively, fDATA is also referred to as the data rate. f DATA f XIN • Turbo Mode 1 = , t DATA = 512 • ( Decimation Ratio + 1) f DATA FIGURE 1. Normalized Digital Filter Response. FILTER RESPONSE 0 –20 –40 Gain (dB) –60 –80 –100 –120 –140 –160 0 50 100 150 Frequency (Hz) 200 250 300 Gain (dB) Conversion Cycle—The term “conversion cycle” usually refers to a discrete A/D conversion operation, such as that performed by a successive approximation converter. As used here, a conversion cycle refers to the tDATA time period. However, each digital output is actually based on the modulator results from the last three tDATA time periods. DIGITAL FILTER The digital filter of the ADS1210/11 computes the output result based on the most recent results from the delta-sigma modulator. The number of modulator results that are used depend on the decimation ratio set in the Command Register. At the most basic level, the digital filter can be thought of as simply averaging the modulator results and presenting this average as the digital output. While the decimation ratio determines the number of modulator results to use, the modulator runs faster at higher Turbo Modes. These two items, together with the ADS1210/11 clock frequency, determine the output data rate: f DATA = f XIN • Turbo Mode 512 • ( Decimation Ratio + 1) FILTER RESPONSE –40 –60 –80 –100 –120 –140 –160 45 46 47 48 49 50 Frequency (Hz) 51 52 53 54 55 FIGURE 2. Digital Filter Response at a Data Rate of 50Hz. FILTER RESPONSE 0 –20 –40 Gain (dB) –60 –80 –100 –120 –140 –160 0 50 100 150 Frequency (Hz) 200 250 300 FILTER RESPONSE –40 –60 Gain (dB) –80 –100 –120 –140 –160 55 56 57 58 59 60 Frequency (Hz) 61 62 63 64 65 Also, since the conversion result is essentially an average, the data rate determines where the resulting notches are in the digital filter. For example, if the output data rate is 1kHz, then a 1kHz input frequency will average to zero during the 1ms conversion cycle. Likewise, a 2kHz input frequency will average to zero, etc. In this manner, the data rate can be used to set specific notch frequencies in the digital filter response (see Figure 1 for the normalized response of the digital filter). For example, if the rejection of power line frequencies is desired, then the data rate can simply be set to the power line frequency. Figures 2 and 3 show the digital filter response for a data rate of 50Hz and 60Hz, respectively. FIGURE 3. Digital Filter Response at a Data Rate of 60Hz. If the effective resolution at a 50Hz or 60Hz data rate is not adequate for the particular application, then power line frequencies could still be rejected by operating the ADS1210/11 at 25/30Hz, 16.7/20Hz, 12.5/15Hz, etc. If a higher data rate is needed, then power line frequencies must either be rejected before conversion (with an analog notch filter) or after conversion (with a digital notch filter running on the main controller). ® 11 ADS1210, 1211 Filter Equation The digital filter is described by the following transfer function:  π • f • N sin    f MOD  | H (f ) | =  π•f  N • sin    f MOD  where N is the Decimation Ratio. 3 the effective resolution of the output data at a given data rate, but there is also an increase in power dissipation. For Turbo Mode Rates 2 and 4, the increase is slight. For rates 8 and 16, the increase is more substantial. See the Typical Performance Curves for more information. In a Turbo Mode Rate of 16, the ADS1210/11 can offer 20 bits of effective resolution at a 1kHz data rate. A comparison of effective resolution versus Turbo Mode Rates and output data rates is shown in Table IV while Table V shows the corresponding noise level in µVrms. Effective Resolution (Bits rms) Data Rate (Hz) 10 20 40 50 60 100 1000 Turbo Mode Rate 1 21.5 21.0 20.0 20.0 19.5 18.0 10.0 Turbo Mode Rate 2 22.0 22.0 21.5 21.5 21.0 20.0 12.5 Turbo Mode Rate 4 22.5 22.0 22.0 21.5 21.5 21.0 15.0 Turbo Mode Rate 8 22.5 22.5 22.0 22.0 21.5 17.5 Turbo Mode Rate 16 This filter has a (sin(x)/x)3 response and is referred to a sinc3 filter. For the ADS1210/11, this type of filter allows the data rate to be changed over a very wide range (nearly four orders of magnitude). However, the –3dB point of the filter is 0.262 times the data rate. And, as can be seen in Figures 1 and 2, the rejection in the stopband (frequencies higher than the first notch frequency) may only be –40dB. These factors must be considered in the overall system design. For example, with a 50Hz data rate, a significant signal at 75Hz may alias back into the passband at 25Hz. The analog front end can be designed to provide the needed attenuation to prevent aliasing, or the system may simply provide this inherently. Another possibility is increasing the data rate and then post filtering with a digital filter on the main controller. Filter Settling The number of modulator results used to compute each conversion result is three times the Decimation Ratio. This means that any step change (or any channel change for the ADS1211) will require at least three conversions to fully settle. However, if the change occurs asynchronously, then at least four conversions are required to ensure complete settling. For example, on the ADS1211, the fourth conversion result after a channel change will be valid (see Figure 4). Significant Analog Input Change or ADS1211 Channel Change Data not Valid Data not Valid Data not Valid 23.0 23.0 23.0 22.5 20.0 TABLE IV. Effective Resolution vs Data Rate and Turbo Mode Rate. (Gain setting of 1 and 10MHz clock.) NOISE LEVEL (µVrms) DATA RATE (Hz) 10 20 40 50 60 100 1000 TURBO MODE RATE 1 2.9 4.3 6.9 8.1 10.5 26.9 6909.7 TURBO MODE RATE 2 1.7 2.1 3.0 3.2 3.9 6.9 1354.5 TURBO MODE RATE 4 1.3 1.7 2.3 2.4 2.6 3.5 238.4 TURBO MODE RATE 8 1.3 1.6 1.8 1.9 2.7 46.6 TURBO MODE RATE 16 1.0 1.0 1.0 1.4 7.8 TABLE V. Noise Level vs Data Rate and Turbo Mode Rate. (Gain setting of 1 and 10MHz clock.) The Turbo Mode feature allows trade-offs to be made between the ADS1210/11 XIN clock frequency, power dissipation, and effective resolution. If a 5MHz clock is available but a 10MHz clock is needed to achieve the desired performance, a Turbo Mode Rate of 2X will result in the same effective resolution. Table VI provides a comparison of effective resolution at various clock frequencies, data rates, and Turbo Mode Rates. DATA RATE (Hz) 60 60 60 60 60 100 100 100 100 100 XIN CLOCK FREQUENCY (MHz) 10 5 2.5 1.25 0.625 10 5 2.5 1.25 0.625 TURBO MODE RATE 1 2 4 8 16 1 2 4 8 16 EFFECTIVE RESOLUTION (Bits rms) 19.5 19.5 19.5 19.5 19.5 18.0 18.0 18.0 18.0 18.0 Valid Data DRDY Valid Data Valid Data Valid Data Serial I/O tDATA FIGURE 4. Asynchronous ADS1210/11 Analog Input Voltage Step or ADS1211 Channel Change to Fully Settled Output Data. TURBO MODE The ADS1210/11 offers a unique Turbo Mode feature which can be used to increase the modulator sampling rate by 2, 4, 8, or 16 times normal. With the increase of modulator sampling frequency, there can be a substantial increase in ® TABLE VI. Effective Resolution vs Data Rate, Clock Frequency, and Turbo Mode Rate. (Gain setting of 1.) 12 ADS1210, 1211 The Turbo Mode Rate (TMR) is programmed via the Sampling Frequency bits of the Command Register. Due to the increase in input capacitor sampling frequency, higher Turbo Mode settings result in lower analog input impedance; AIN Impedance (Ω) = (10MHz/fXIN)•4.3E6/(G•TMR) where G is the gain setting. Because the modulator rate also changes in direct relation to the Turbo Mode setting, higher values result in a lower impedance for the REFIN input: REFIN Impedance (Ω) = (10MHz/fXIN)•1E6/TMR The Turbo Mode Rate can be set to 1, 2, 4, 8, or 16. Consult the graphs shown in the Typical Performance Curves for full details on the performance of the ADS1210/11 operating in different Turbo Mode Rates. Keep in mind that higher Turbo Mode Rates result in fewer available gain settings as shown in Table II. PROGRAMMABLE GAIN AMPLIFIER The programmable gain amplifier gain setting is programmed via the PGA Gain bits of the Command Register. Changes in the gain setting (G) of the programmable gain amplifier results in an increase in the input capacitor sampling frequency. Thus, higher gain settings result in a lower analog input impedance: AIN Impedance (Ω) = (10MHz/fXIN)•4.3E6/(G•TMR) where TMR is the Turbo Mode Rate. Because the modulator speed does not depend on the gain setting, the input impedance seen at REFIN does not change. The PGA can be set to gains of 1, 2, 4, 8, or 16. These gain settings with their resulting full-scale range and typical voltage range are shown in Table I. Keep in mind that higher Turbo Mode Rates result in fewer available gain settings as shown in Table II. SOFTWARE GAIN The excellent performance, flexibility, and low cost of the ADS1210/11 allow the converter to be considered for designs which would not normally need a 24-bit ADC. For example, many designs utilize a 12-bit converter and a highgain INA or PGA for digitizing low amplitude signals. For some of these cases, the ADS1210/11 by itself may be a solution, even though the maximum gain is limited to 16. To get around the gain limitation, the digital result can simply be shifted up by “n” bits in the main controller— resulting in a gain of “n” times G, where G is the gain setting. While this type of manipulation of the output data is obvious, it is easy to miss how much the gain can be increased in this manner on a 24-bit converter. For example, shifting the result up by three bits when the ADS1210/11 is set to a gain of 16 results in an effective gain of 128. At lower data rates, the converter can easily provide more than 12 bits of resolution. Even higher gains are possible. The limitation is a combination of the needed data rate, desired noise performance, and desired linearity. CALIBRATION The ADS1210/11 offers several different types of calibration, and the particular calibration desired is programmed via the Command Register. In the case of Background Calibration, the calibration will repeat at regular intervals indefinitely. For all others, the calibration is performed once and then normal operation is resumed. Each type of calibration is covered in detail in their respective section. In general, calibration is recommended immediately after power-on and whenever there is a “significant” change in the operating environment. The amount of change which should cause a re-calibration is dependent on the application, effective resolution, etc. Where high accuracy is important, re-calibration should be done on changes in temperature and power supply. In all cases, re-calibration should be done when the gain, Turbo Mode, or data rate is changed. After a calibration has been accomplished, the Offset Calibration Register and the Full-Scale Calibration Register contain the results of the calibration. The data in these registers are accurate to the effective resolution of the ADS1210/11’s mode of operation during the calibration. Thus, these values will show a variation (or noise) equivalent to a regular conversion result. For those cases where this error must be reduced, it is tempting to consider running the calibration at a slower data rate and then increasing the converter’s data rate after the calibration is complete. Unfortunately, this will not work as expected. The reason is that the results calculated at the slower data rate would not be valid for the higher data rate. Instead, the calibration should be done repeatedly. After each calibration, the results can be read and stored. After the desired number of calibrations, the main controller can compute an average and write this value into the calibration registers. The resulting error in the calibration values will be reduced by the square root of the number of calibrations which were averaged. The calibration registers can also be used to provide system offset and gain corrections separate from those computed by the ADS1210/11. For example, these might be burned into E2PROM during final product testing. On power-on, the main controller would load these values into the calibration registers. A further possibility is a look-up table based on the current temperature. Note that the values in the calibration registers will vary from configuration to configuration and from part to part. There is no method of reliably computing what a particular calibration register should be to correct for a given amount of system error. It is possible to present the ADS1210/11 with a known amount of error, perform a calibration, read the desired calibration register, change the error value, perform another calibration, read the new value and use these values to interpolate an intermediate value. ® 13 ADS1210, 1211 Normal Mode Valid Data DRDY SC(1) Serial I/O tDATA Valid Data Offset Calibration on Internal Offset(2) Self-Calibration Mode Full-Scale Calibration on Internal Full-Scale Analog Input Conversion Normal Mode Valid Data Valid Data NOTES: (1) SC = Self-Calibration instruction. (2) In Slave Mode, this function requires 4 cycles. FIGURE 5. Self-Calibration Timing. Self-Calibration A self-calibration is performed after the bits 001 have been written to the Command Register Operation Mode bits (MD2 through MD0). This initiates the following sequence at the start of the next conversion cycle (see Figure 5). The DRDY signal will not go LOW but will remain HIGH and will continue to remain HIGH throughout the calibration sequence. The inputs to the sampling capacitor are disconnected from the converter’s analog inputs and are shorted together. An offset calibration is performed over the next three conversion periods (four in Slave Mode). Then, the input to the sampling capacitor is connected across REFIN, and a full-scale calibration is performed over the next three conversions. After this, the Operation Mode bits are reset to 000 (normal mode) and the input capacitor is reconnected to the input. Conversions proceed as usual over the next three cycles in order to fill the digital filter. DRDY remains HIGH during this time. On the start of the fourth cycle, DRDY goes LOW indicating valid data and resumption of normal operation. System Offset Calibration A system offset calibration is performed after the bits 010 have been written to the Command Register Operation Mode bits (MD2 through MD0). This initiates the following sequence (see Figure 6). At the start of the next conversion cycle, the DRDY signal will not go LOW but will remain HIGH and will continue to remain HIGH throughout the calibration sequence. The offset calibration will be performed on the differential input voltage present at the converter’s input over the next three conversion periods (four in Slave Mode). When this is done, the Operation Mode bits are reset to 000 (Normal Mode). A single conversion is done with DRDY HIGH. After this conversion, the DRDY signal goes LOW indicating resumption of normal operation. Normal operation returns within a single conversion cycle because it is assumed that the input voltage at the converter’s input is not removed immediately after the offset calibration is performed. In this case, the digital filter already contains a valid result. For full system calibration, offset calibration must be performed first and then full-scale calibration. In addition, the offset calibration error will be the rms sum of the conversion error and the noise on the system offset voltage. See the System Calibration Limits section for information regarding the limits on the magnitude of the system offset voltage. System Full-Scale Calibration A system full-scale calibration is performed after the bits 011 have been written to the Command Register Operation Mode bits (MD2 through MD0). This initiates the following sequence (see Figure 7). At the start of the next conversion cycle, the DRDY signal will not go LOW but will remain HIGH and will continue to remain HIGH throughout the calibration sequence. The full-scale calibration will be performed on the differential input voltage (2 • REFIN/G) present at the converter’s input over the next three conversion periods (four in Slave Mode). When this is done, the Operation Mode bits are reset to 000 (Normal Mode). A single conversion is done with DRDY HIGH. After this conversion, the DRDY signal goes LOW indicating resumption of normal operation. Normal Mode Valid Data DRDY SOC(1) Serial I/O tDATA Valid Data System Offset Calibration Mode Offset Calibration on System Offset(2) Normal Mode Analog Possibly Valid Input Conversion Data Possibly Valid Data Normal Mode Valid Data DRDY SFSC(1) Serial I/O tDATA Valid Data System Full-Scale Calibration Mode Full-Scale Calibration on System Full-Scale(2) Normal Mode Analog Possibly Input Valid Conversion Data Possibly Valid Data NOTES: (1) SOC = System Offset Calibration instruction. (2) In Slave Mode, this function requires 4 cycles. NOTES: (1) SFSC = System Full-Scale Calibration instruction. (2) In Slave Mode, this function requires 4 cycles. FIGURE 6. System Offset Calibration Timing. ® FIGURE 7. System Full-Scale Calibration Timing. 14 ADS1210, 1211 Normal operation returns within a single conversion cycle because it is assumed that the input voltage at the converter’s input is not removed immediately after the full-scale calibration is performed. In this case, the digital filter already contains a valid result. For full system calibration, offset calibration must be performed first and then full-scale calibration. The calibration error will be a sum of the rms noise on the conversion result and the input signal noise. See the System Calibration Limits section for information regarding the limits on the magnitude of the system full-scale voltage. Pseudo System Calibration The Pseudo System Calibration is performed after the bits 100 have been written to the Command Register Operation Mode bits (MD2 through MD0). This initiates the following sequence (see Figure 8). At the start of the next conversion cycle, the DRDY signal will not go LOW but will remain HIGH and will continue to remain HIGH throughout the calibration sequence. The offset calibration will be performed on the differential input voltage present at the converter’s input over the next three conversion periods (four in Slave Mode). Then, the input to the sampling capacitor is disconnected from the converter’s analog input and connected across REFIN. A gain calibration is performed over the next three conversions. After this, the Operation Mode bits are reset to 000 (normal mode) and the input capacitor is then reconnected to the input. Conversions proceed as usual over the next three cycles in order to fill the digital filter. DRDY remains HIGH during this time. On the next cycle, the DRDY signal goes LOW indicating valid data and resumption of normal operation. The system offset calibration range of the ADS1210/11 is limited and is listed in the Specifications Table. For more information on how to use these specifications, see the System Calibration Limits section. To calculate VOS, use 2 • REFIN / GAIN for VFS. Background Calibration The Background Calibration Mode is entered after the bits 101 have been written to the Command Register Operation Mode bits (MD2 through MD0). This initiates the following continuous sequence (see Figure 9). At the start of the next conversion cycle, the DRDY signal will not go LOW but will remain HIGH. The inputs to the sampling capacitor are disconnected from the converter’s analog input and shorted together. An offset calibration is performed over the next three conversion periods (in Slave Mode, the very first offset calibration requires four periods and all subsequent offset calibrations require three periods). Then, the input capacitor is reconnected to the input. Conversions proceed as usual over the next three cycles in order to fill the digital filter. DRDY remains HIGH during this time. On the next cycle, the DRDY signal goes LOW indicating valid data. Normal Mode Valid Data DRDY PSC(1) Serial I/O tDATA Valid Data Offset Calibration on System Offset(2) Pseudo System Calibration Mode Full-Scale Calibration on Internal Full-Scale Analog Input Conversion Normal Mode Valid Data Valid Data NOTES: (1) PSC = Pseudo System Calibration instruction. (2) In Slave Mode, this function requires 4 cycles. FIGURE 8. Pseudo System Calibration Timing. Normal Mode Valid Data DRDY BC(1) Serial I/O tDATA Valid Data Background Calibration Mode Offset Calibration on Internal Offset(2) Analog Input Conversion Full-Scale Calibration on Internal Full-Scale Analog Input Conversion Cycle Repeats with Offset Calibration NOTES: (1) BC = Background Calibration instruction. (2) In Slave Mode, the very first offset calibration will require 4 cycles. All subsequent offset calibrations will require 3 cycles. FIGURE 9. Background Calibration Timing. ® 15 ADS1210, 1211 Also, during this cycle, the sampling capacitor is disconnected from the converter’s analog input and is connected across REFIN. A gain calibration is initiated and proceeds over the next three conversions. After this, the input capacitor is once again connected to the analog input. Conversions proceed as usual over the next three cycles in order to fill the digital filter. DRDY remains HIGH during this time. On the next cycle, the DRDY signal goes LOW indicating valid data, the input to the sampling capacitor is shorted, and an offset calibration is initiated. At this point, the Background Calibration sequence repeats. In essence, the Background Calibration Mode performs continuous self-calibration where the offset and gain calibrations are interleaved with regular conversions. Thus, the data rate is reduced by a factor of 6. The advantage is that the converter is continuously adjusting to environmental changes such as ambient or component temperature (due to airflow variations). The ADS1210/11 will remain in the Background Calibration Mode indefinitely. To move to any other mode, the Command Register Operation Mode bits (MD2 through MD0) must be set to the appropriate values. System Calibration Offset and Full-Scale Calibration Limits The System Offset and Full-Scale Calibration range of the ADS1210/11 is limited and is listed in the Specifications Table. The range is specified as: (VFS – | VOS |) < 1.3 • (2 • REFIN)/GAIN (VFS – | VOS |) > 0.7 • (2 • REFIN)/GAIN where VFS is the system full-scale voltage and | VOS | is the absolute value of the system offset voltage. In the following discussion, keep in mind that these voltages are differential voltages. For example, with the internal reference (2.5V) and a gain of two, the previous equations become (after some manipulation): VFS – 3.25 < VOS < VFS – 1.75 If VFS is perfect at 2.5V (positive full-scale), then VOS must be greater than –0.75V and less than 0.75V. Thus, when offset calibration is performed, the positive input can be no more than 0.75V below or above the negative input. If this range is exceeded, the ADS1210/11 may not calibrate properly. This calculation method works for all gains other than one. For a gain of one and the internal reference (2.5V), the equation becomes: VFS – 6.5 < VOS < VFS – 3.5 With a 5V positive full-scale input, VOS must be greater than –1.5V and less than 1.5V. Since the offset represents a common-mode voltage and the input voltage range in a gain of one is 0V to 5V, a common-mode voltage will cause the actual input voltage to possibly go below 0V or above 5V. The specifications also show that for the specifications to be valid, the input voltage must not go below AGND by more than 30mV or above AVDD by more than 30mV. ® This will be an important consideration in many systems which use a 2.5V or greater reference, as the input range is constrained by the expected power supply variations. In addition, the expected full-scale voltage will impact the allowable offset voltage (and vice-versa) as the combination of the two must remain within the power supply and ground potentials, regardless of the results obtained via the range calculation shown previously. There are only two solutions to this constraint: either the system design must ensure that the full-scale and offset voltage variations will remain within the power supply and ground potentials, or the part must be used in a gain of 2 or greater. SLEEP MODE The Sleep Mode is entered after the bits 110 have been written to the Command Register Operation Mode bits (MD2 through MD0). This mode is exited by entering a new mode into the MD2-MD0 bits. The Sleep Mode causes the analog section and a good deal of the digital section to power down. For full analog power down, the VBIAS generator and the internal reference must also be powered down by setting the BIAS and REFO bits in the Command Register accordingly. The power dissipation shown in the Specifications Table is with the internal reference and the VBIAS generator disabled. To initiate serial communication with the converter while it is in Sleep Mode, one of the following procedures must be used: If CS is being used, simply taking CS LOW will enable serial communication to proceed normally. If CS is not being used (tied LOW) and the ADS1210/11 is in the Master Mode, then a falling edge must be produced on the SDIO line. If SDIO is LOW, the SDIO line must be taken HIGH for 2 • tXIN periods (minimum) and then taken LOW. Alternatively, SDIO can be forced HIGH after putting the ADS1210/11 to “sleep” and then taken LOW when the Sleep Mode is to be exited. Finally, if CS is not being used (tied LOW) and the ADS1210/11 is in the Slave Mode, then simply sending a normal Instruction Register command will re-establish communication. Once serial communication is resumed, the Sleep Mode is exited by changing the MD2-MD0 bits to any other mode. When a new mode (other than Sleep) has been entered, the ADS1210/11 will execute a very brief internal power-up sequence of the analog and digital circuitry. Once this has been done, one normal conversion cycle is performed before the new mode is actually entered. At the end of this conversion cycle, the new mode takes effect and the converter will respond accordingly. The DRDY signal will remain HIGH through the first conversion cycle. It will also remain HIGH through the second, even if the new mode is the Normal Mode. If the VBIAS generator and/or the internal reference have been disabled, then they must be manually re-enabled via the appropriate bits in the Command Register. In addition, the internal reference will have to charge the external bypass capacitor(s) and possibly other circuitry. There may also be ADS1210, 1211 16 considerations associated with VBIAS and the settling of external circuitry. All of these must be taken into account when determining the amount of time required to resume normal operation. The timing diagram shown in Figure 10 does not take into account the settling of external circuitry. Sleep Mode Change to Normal Mode Occurs Here One (Other Normal Modes Conversion Start Here) Data Not Valid Valid Data(1) Valid Data(1) DRDY Serial I/O tDATA NOTE: (1) Assuming that the external circuitry has been stable for the previous three tDATA periods. FIGURE 10. Sleep Mode to Normal Mode Timing. ANALOG OPERATION ANALOG INPUT The input impedance of the analog input changes with ADS1210/11 clock frequency (fXIN), gain (G), and Turbo Mode Rate (TMR). The relationship is: AIN Impedance (Ω) = (10MHz/fXIN)•4.3E6/(G•TMR) Figure 11 shows the basic input structure of the ADS1210. The ADS1211 includes an input multiplexer, but this has little impact on the analysis of the input structure. The impedance is directly related to the sampling frequency of the input capacitor. The XIN clock rate sets the basic sampling rate in a gain of 1 and Turbo Mode Rate of 1. Higher gains and higher Turbo Mode Rates result in an increase of the sampling rate, while slower clock (XIN) frequencies result in a decrease. the analog signal must reside within this range, the linearity of the ADS1210/11 is only guaranteed when the actual analog input voltage resides within a range defined by AGND –30mV and AVDD +30mV. This is due to leakage paths which occur within the part when AGND and AVDD are exceeded. For this reason, the 0V to 5V input range (gain of 1 with a 2.5V reference) must be used with caution. Should AVDD be 4.75V, the analog input signal would swing outside of the guaranteed specifications of the device. Designs utilizing this mode of operation should consider limiting the span to a slightly smaller range. Common-mode voltages are also a significant concern in this mode and must be carefully analyzed. An input voltage range of 0.75V to 4.25V is the smallest span that is allowed if a full system calibration will be performed (see the Calibration section for more details). This also assumes an offset error of zero. A better choice would be 0.5V to 4.5V (a full-scale range of 9V). This span would allow some offset error, gain error, power supply drift, and common-mode voltage while still providing full system calibration over reasonable variation in each of these parameters. The actual input voltage exceeding AGND or AVDD should not be a concern in higher gain settings as the input voltage range will reside well within 0V to 5V. This is true unless the common-mode voltage is large enough to place positive fullscale or negative full-scale outside of the AGND to AVDD range. REFERENCE INPUT The input impedance of the REFIN input changes with clock frequency (fXIN) and Turbo Mode Rate (TMR). The relationship is: REFIN Impedance (Ω) = (10MHz/fXIN)•1E6/TMR Unlike the analog input, the reference input impedance has a negligible dependency on the PGA gain setting. The reference input voltage can vary between 2V and 3V. A nominal voltage of 2.5V appears at REFOUT, and this can be directly connected to REFIN. Higher reference voltages will cause the full-scale range to increase while the internal circuit noise of the converter remains approximately the same. This will increase the LSB weight but not the internal noise, resulting in increased signal-to-noise ratio and effective resolution. Likewise, lower reference voltages will decrease the signal-to-noise ratio and effective resolution. REFERENCE OUTPUT The ADS1210/11 contains an internal +2.5V reference. Tolerances, drift, noise, and other specifications for this reference are given in the Specification Table. Note that it is not designed to sink or to source more than 1mA of current. In addition, loading the reference with a dynamic or variable load is not recommended. This can result in small changes in reference voltage as the load changes. Finally, for designs approaching or exceeding 20 bits of effective resolution, a low-noise external reference is recommended as the internal reference may not provide adequate performance. ® RSW (8kΩ typical) AIN High Impedance > 1GΩ CINT 8pF Typical VCM Switching Frequency = fSAMP FIGURE 11. Analog Input Structure. This input impedance can become a major point of consideration in some designs. If the source impedance of the input signal is significant or if there is passive filtering prior to the ADS1210/11, then a significant portion of the signal can be lost across this external impedance. How significant this effect is depends on the desired system performance. There are two restrictions on the analog input signal to the ADS1210/11. Under no conditions should the current into or out of the analog inputs exceed 10mA. In addition, while 17 ADS1210, 1211 R1 3kΩ ±10V ±10V R2 3kΩ R3 1kΩ R4 1kΩ AINP AINN AGND VBIAS DVDD C1 12pF GND CS REFIN REFOUT AVDD MODE ADS1210 DRDY DGND DSYNC XIN XTAL C2 12pF DGND XOUT DGND SDOUT SDIO SCLK DVDD DVDD AVDD AGND 1.0µF DGND FIGURE 12. ±10V Input Configuration Using VBIAS. The circuitry which generates the +2.5V reference can be disabled via the Command Register and will result in a lower power dissipation. The reference circuitry consumes a little over 1.6mA of current with no external load. When the ADS1210/11 is in its default state, the internal reference is enabled. VBIAS The VBIAS output voltage is dependent on the reference input (REFIN) voltage and is approximately 1.33 times as great. This output is used to bias input signals such that bipolar signals with spans of greater than 5V can be scaled to match the input range of the ADS1210/11. Figure 12 shows a connection diagram which will allow the ADS1210/11 to accept a ±10V input signal (40V full-scale range). This method of scaling and offsetting the ±20V differential input signal will be a concern for those requiring minimum power dissipation. VBIAS will supply 1.68mA for every channel connected as shown. For the ADS1211, the current draw is within the specifications for VBIAS, but, at 12mW, the power dissipation is significant. If this is a concern, resistors R1 and R2 can be set to 9kΩ and R3 and R4 to 3kΩ. This will reduce power dissipation by one-third. In addition, these resistors can also be set to values which will provide any arbitrary input range. In all cases, the maximum current into or out of VBIAS should not exceed its specification of 10mA. Note that the connection diagram shown in Figure 12 causes a constant amount of current to be sourced by VBIAS. This will be very important in higher resolution designs as the voltage at VBIAS will not change with loading, as the load is constant. However, if the input signal is single-ended and one side of the input is grounded, the load will not be constant and VBIAS will change slightly with the input signal. Also, in all cases, note that noise on VBIAS introduces a common-mode error signal which is rejected by the converter. The 3k resistors should not be used as part of an anti-alias filter with a capacitor across the inputs. The ADS1210 samples charge from the capacitor which has the effect of introducing an offset in the measurement. This might be acceptable for relative differential measurements. The circuitry to generate VBIAS is disabled when the ADS1210/11 is in its default state, and it must be enabled, via the Command Register, in order for the VBIAS voltage to ® be present. When enabled, the VBIAS circuitry consumes approximately 1mA with no external load. On power-up, external signals may be present before VBIAS is enabled. This can create a situation in which a negative voltage is applied to the analog inputs (–2.5V for the circuit shown in Figure 12), reverse biasing the negative input protection diode. This situation should not be a problem as long as the resistors R1 and R2 limit the current being sourced by each analog input to under 10mA (a potential of 0V at the analog input pin should be used in the calculation). DIGITAL OPERATION SYSTEM CONFIGURATION The Micro Controller (MC) consists of an ALU and a register bank. The MC has two states: power-on reset and convert. In the power-on reset state, the MC resets all the registers to their default state, sets up the modulator to a stable state, and performs self-calibration at a 850Hz data rate. After this, it enters the convert mode, which is the normal mode of operation for the ADS1210/11. The ADS1210/11 has 5 internal registers, as shown in Table VII. Two of these, the Instruction Register and the Command Register, control the operation of the converter. The Data Output Register (DOR) contains the result from the most recent conversion. The Offset and Full-Scale Calibration Registers (OCR and FCR) contain data used for correcting the internal conversion result before it is placed into the DOR. The data in these two registers may be the result of a calibration routine, or they may be values which have been written directly via the serial interface. INSR DOR CMR OCR FCR Instruction Register Data Output Register Command Register Offset Calibration Register Full-Scale Calibration Register 8 Bits 24 Bits 32 Bits 24 Bits 24 Bits TABLE VII. ADS1210/11 Registers. Communication with the ADS1210/11 is controlled via the Instruction Register (INSR). Under normal operation, the INSR is written as the first part of each serial communication. The instruction that is sent determines what type of communication will occur next. It is not possible to read the INSR. 18 ADS1210, 1211 The Command Register (CMR) controls all of the ADS1210/ 11’s options and operating modes. These include the PGA gain setting, the Turbo Mode Rate, the output data rate (decimation ratio), etc. The CMR is the only 32-bit register within the ADS1210/11. It, and all the remaining registers, may be read from or written to. Instruction Register (INSR) The INSR is an 8-bit register which commands the serial interface either to read or to write “n” bytes beginning at the specified register location. Table VIII shows the format for the INSR. MSB R/W MB1 MB0 0 A3 A2 A1 LSB A0 Each serial communication starts with the 8-bits of the INSR being sent to the ADS1210/11. This directs the remainder of the communication cycle, which consists of n bytes being read from or written to the ADS1210/11. The read/write bit, the number of bytes n, and the starting register address are defined, as shown in Table VIII. When the n bytes have been transferred, the INSR is complete. A new communication cycle is initiated by sending a new INSR (under restrictions outlined in the Interfacing section). Command Register (CMR) The CMR controls all of the functionality of the ADS1210/ 11. The new configuration takes effect on the negative transition of SCLK for the last bit in each byte of data being written to the command register. The organization of the CMR is shown in Table X. Most Significant Bit Byte 3 DSYNC(1) BIAS REFO 0 Off DF U/B BD MSB SDL DRDY 0 Defaults TABLE VIII. Instruction Register. R/W (Read/Write) Bit—For a write operation to occur, this bit of the INSR must be 0. For a read, this bit must be 1, as follows: R/W 0 1 Write Read 1 On 0 Two’s 0 Biplr 0 MSByte 0 MSB 0 SDIO NOTE: (1) DSYNC is Write only, DRDY is Read only. Byte 2 MD2 MD1 MD0 G2 G1 000 Gain 1 Byte 1 SF2 SF1 SF0 DR12 DR11 DR10 DR9 00000 Byte 0 DR7 DR6 DR5 DR4 DR3 Least Significant Bit DR2 DR1 DR0 Defaults DR8 Defaults G0 CH1 CH0 Defaults 000 Normal Mode 00 Channel 1 MB1, MB0 (Multiple Bytes) Bits—These two bits are used to control the word length (number of bytes) of the read or write operation, as follows: MB1 0 0 1 1 MB0 0 1 0 1 1 Byte 2 Bytes 3 Bytes 4 Bytes 000 Turbo Mode Rate of 1 (00000) 0001 0111 (23) Data Rate of 814Hz A3-A0 (Address) Bits—These four bits select the beginning register location which will be read from or written to, as shown in Table IX. Each subsequent byte will be read from or written to the next higher location. (If the BD bit in the Command Register is set, each subsequent byte will be read from the next lower location. This bit does not affect the write operation.) If the next location is not defined in Table IX, then the results are unknown. Reading or writing continues until the number of bytes specified by MB1 and MB0 have been transferred. A3 0 0 0 0 0 0 0 1 1 1 1 1 1 A2 0 0 0 1 1 1 1 0 0 0 1 1 1 A1 0 0 1 0 0 1 1 0 0 1 0 0 1 A0 0 1 0 0 1 0 1 0 1 0 0 1 0 REGISTER BYTE Data Output Register Byte 2 (MSB) Data Output Register Byte 1 Data Output Register Byte 0 (LSB) Command Register Byte 3 (MSB) Command Register Byte 2 Command Register Byte 1 Command Register Byte 0 (LSB) Offset Cal Register Byte 2 (MSB) Offset Cal Register Byte 1 Offset Cal Register Byte 0 (LSB) Full-Scale Cal Register Byte 2 (MSB) Full-Scale Cal Register Byte 1 Full-Scale Cal Register Byte 0 (LSB) TABLE X. Organization of the Command Register and Default Status. BIAS (Bias Voltage) Bit—The BIAS bit controls the VBIAS output state—either on (1.33 • REFIN) or off (disabled), as follows: BIAS 0 1 VBIAS GENERATOR Off On VBIAS STATUS Disabled 1.33•REFIN Default The VBIAS circuitry consumes approximately 1mA of steady state current with no external load. See the VBIAS section for full details. When the internal reference (REFOUT) is connected to the reference input (REFIN), VBIAS is 3.3V, nominal. REFO (Reference Output) Bit—The REFO bit controls the internal reference (REFOUT) state, either on (2.5V) or off (disabled), as follows: REFO 0 1 INTERNAL REFERENCE Off On REFOUT STATUS High Impedance 2.5V Default Note: MSB = Most Significant Byte, LSB = Least Significant Byte TABLE IX. A3-A0 Addressing. The internal reference circuitry consumes approximately 1.6mA of steady state current with no external load. See the Reference Output section for full details on the internal reference. ® 19 ADS1210, 1211 DF (Data Format) Bit—The DF bit controls the format of the output data, either Two’s Complement or Offset Binary, as follows: DF 0 FORMAT Two’s Complement Offset Binary ANALOG INPUT +Full-Scale Zero –Full Scale +Full-Scale Zero –Full-scale DIGITAL OUTPUT 7FFFFFH 000000H 800000H FFFFFFH 800000H 000000H Default SDL (Serial Data Line) Bit—The SDL bit controls which pin on the ADS1210/11 will be used as the serial data output pin, either SDIO or SDOUT, as follows: SDL 0 1 SERIAL DATA OUTPUT PIN SDIO SDOUT Default 1 These two formats are the same for all bits except the most significant, which is simply inverted in one format vs the other. This bit only applies to the Data Output Register—it has no effect on the other registers. U/B (Unipolar) Bit—The U/B bit controls the limits imposed on the output data, as follows: U/B 0 1 MODE Bipolar Unipolar LIMITS None Zero to +Full-Scale only Default If SDL is LOW, then SDIO will be used for both input and output of serial data—see the Timing section for more details on how the SDIO pin transitions between these two states. In addition, SDOUT will remain in a tri-state condition at all times. Important Note: Since the default condition is SDL LOW, SDIO has the potential of becoming an output once every data output cycle if the ADS1210/11 is in the Master Mode. This will occur until the Command Register can be written and the SDL bit set HIGH. See the Interfacing section for more information. DRDY (Data Ready) Bit—The DRDY bit is a read only bit which reflects the state of the ADS1210/11’s DRDY output pin, as follows: DRDY 0 1 MEANING Data Ready Data Not Ready The particular mode has no effect on the actual full-scale range of the ADS1210/11, data format, or data format vs input voltage. In the bipolar mode, the ADS1210/11 operates normally. In the unipolar mode, the conversion result is limited to positive values only (zero included). This bit only controls what is placed in the Data Output Register. It has no effect on internal data. When cleared, the very next conversion will produce a valid bipolar result. BD (Byte Order) Bit—The BD bit controls the order in which bytes of data are read, either most significant byte first or least significant byte, as follows: BD 0 BYTE ACCESS ORDER Most Significant to Least Significant Byte Least Significant to Most Significant Byte Default DSYNC (Data Synchronization) Bit—The DSYNC bit is a write only bit which occupies the same location as DRDY. When a ‘one’ is written to this location, the affect on the ADS1210/11 is the same as if the DSYNC input pin had been taken LOW and returned HIGH. That is, the modulator count for the current conversion cycle will be reset to zero. DSYNC 0 1 MEANING No Change in Modulator Count Modulator Count Reset to Zero 1 Note that when BD is clear and a multi-byte read is initiated, A3-A0 of the Instruction Register is the address of the most significant byte and subsequent bytes reside at higher addresses. If BD is set, then A3-A0 is the address of the least significant byte and subsequent bytes reside at lower addresses. The BD bit only affects read operations, it has no affect on write operations. MSB (Bit Order) Bit—The MSB bit controls the order in which bits within a byte of data are read, either most significant bit first or least significant bit, as follows: MSB 0 1 BIT ORDER Most Significant Bit First Least Significant Bit First Default The DSYNC bit is provided in order to reduce the number of interface signals that are needed between the ADS1210/11 and the main controller. Consult “Making Use of DSYNC” in the Serial Interface section for more information. MD2-MD0 (Operating Mode) Bits—The MD2-MD0 bits initiate or enable the various calibration sequences, as follows: MD2 0 0 0 0 1 1 1 1 MD1 0 0 1 1 0 0 1 1 MD0 0 1 0 1 0 1 0 1 OPERATING MODE Normal Mode Self-Calibration System Offset Calibration System Full-Scale Calibration Pseudo System Calibration Background Calibration Sleep Reserved The MSB bit only affects read operations, it has no affect on write operations. ® The Normal Mode, Background Calibration Mode, and Sleep Mode are permanent modes and the ADS1210/11 will remain in these modes indefinitely. All other modes are temporary and will revert to Normal Mode once the appropriate actions are complete. See the Calibration and Sleep Mode sections for more information. 20 ADS1210, 1211 Data Rate (Hz) 1000 500 250 100 60 50 20 10 Decimation Ratio 19 38 77 194 325 390 976 1952 DR12 0 0 0 0 0 0 0 0 DR11 0 0 0 0 0 0 0 0 DR10 0 0 0 0 0 0 0 1 DR9 0 0 0 0 0 0 1 1 DR8 0 0 0 0 1 1 1 1 DR7 0 0 0 1 0 1 1 1 DR6 0 0 1 1 1 0 1 0 DR5 0 1 0 0 0 0 0 1 DR4 1 0 0 0 0 0 1 0 DR3 0 0 1 0 0 0 0 0 DR2 0 1 1 0 1 1 0 0 DR1 1 1 0 1 0 1 0 0 DR0 1 0 1 0 1 0 0 0 Table XI. Decimation Ratios vs Data Rates (Turbo Mode rate of 1 and 10MHz clock). G2-G0 (PGA Control) Bits—The G2-G0 bits control the gain setting of the PGA, as follows: G2 0 0 0 0 1 G1 0 0 1 1 0 G0 0 1 0 1 0 GAIN SETTING 1 2 4 8 16 AVAILABLE TURBO MODE RATES 1, 2, 4, 8, 16 1, 2, 4, 8 1, 2, 4 1, 2 1 Default The input capacitor sampling frequency and modulator rate can be calculated from the following equations: fSAMP = G • TMR • fXIN / 512 fMOD = TMR • fXIN / 512 where G is the gain setting and TMR is the Turbo Mode Rate. The sampling frequency of the input capacitor directly relates to the analog input impedance. The modulator rate relates to the power consumption of the ADS1210/11 and the output data rate. See the Turbo Mode, Analog Input, and Reference Input sections for more details. DR12-DR0 (Decimation Ratio) Bits—The DR12-DR0 bits control the decimation ratio of the ADS1210/11. In essence, these bits set the number of modulator results which are used in the digital filter to compute each individual conversion result. Since the modulator rate depends on both the ADS1210/11 clock frequency and the Turbo Mode Rate, the actual output data rate is given by the following equation: fDATA = fXIN • TMR / (512 • (Decimation Ratio + 1)) where TMR is the Turbo Mode Rate. Table XI shows various data rates and corresponding decimation ratios (with a 10MHz clock). Valid decimation ratios are from 19 to 8000. Outside of this range, the digital filter will compute results incorrectly due to inadequate or too much data. Data Output Register (DOR) The DOR is a 24-bit register which contains the most recent conversion result (see Table XII). This register is updated with a new result just prior to DRDY going LOW. If the contents of the DOR are not read within a period of time defined by 1/fDATA –12•(1/fXIN), then a new conversion result will overwrite the old. (DRDY is forced HIGH prior to the DOR update, unless a read is in progress). Most Significant Bit DOR23 DOR22 DOR21 Byte 2 DOR20 DOR19 DOR18 DOR17 DOR16 The gain is partially implemented by increasing the input capacitor sampling frequency, which is given by the following equation: fSAMP = G • TMR • fXIN /512 where G is the gain setting and TMR is the Turbo Mode Rate. The product of G and TMR cannot exceed 16. The sampling frequency of the input capacitor directly relates to the analog input impedance. See the Programmable Gain Amplifier and Analog Input sections for more details. CH1-CH0 (Channel Selection) Bits—The CH1 and CH0 bits control the input multiplexer on the ADS1211, as follows: CH1 0 0 1 1 CH0 0 1 0 1 ACTIVE INPUT Channel Channel Channel Channel 1 2 3 4 Default (For the ADS1210, CH1 and CH0 must always be zero.) The channel change takes effect when the last bit of byte 2 has been written to the Command Register. Output data will not be valid for the next three conversions despite the DRDY signal indicating that data is ready. On the fourth time that DRDY goes LOW after a channel change has been written to the Command Register, valid data will be present in the Data Output Register (see Figure 4). SF2-SF0 (Turbo Mode Rate) Bits—The SF2-SF0 bits control the input capacitor sampling frequency and modulator rate, as follows: TURBO MODE RATE 1 2 4 8 16 AVAILABLE PGA SETTINGS 1, 2, 4, 8, 16 1, 2, 4, 8 1, 2, 4 1, 2 1 Default Byte 1 DOR15 DOR14 DOR13 DOR12 DOR11 DOR10 DOR9 DOR8 Byte 0 DOR7 DOR6 DOR5 DOR4 DOR3 Least Significant Bit DOR2 DOR1 DOR0 TABLE XII. Data Output Register. The contents of the DOR can be in Two’s Complement or Offset Binary format. This is controlled by the DF bit of the Command Register. In addition, the contents can be limited to unipolar data only with the U/B bit of the Command Register. ® SF2 0 0 0 0 1 SF1 0 0 1 1 0 SF0 0 1 0 1 0 21 ADS1210, 1211 Offset Calibration Register (OCR) The OCR is a 24-bit register which contains the offset correction factor that is applied to the conversion result before it is placed in the Data Output Register (see Table XIII). In most applications, the contents of this register will be the result of either a self-calibration or a system calibration. The OCR is both readable and writeable via the serial interface. For applications requiring a more accurate offset calibration, multiple calibrations can be performed, each resulting OCR value read, the results averaged, and a more precise offset calibration value written back to the OCR. The actual OCR value will change from part-to-part and with configuration, temperature, and power supply. Thus, the actual OCR value for any arbitrary situation cannot be accurately predicted. That is, a given system offset could not be corrected simply by measuring the error externally, computing a correction factor, and writing that value to the OCR. In addition, be aware that the contents of the OCR are not used to directly correct the conversion result. Rather, the correction is a function of the OCR value. This function is linear and two known points can be used as a basis for interpolating intermediate values for the OCR. Consult the Calibration section for more details. Most Significant Bit OCR23 OCR22 OCR21 Byte 2 OCR20 OCR19 OCR18 OCR17 OCR16 The actual FCR value will change from part-to-part and with configuration, temperature, and power supply. Thus, the actual FCR value for any arbitrary situation cannot be accurately predicted. That is, a given system full-scale error cannot be corrected simply by measuring the error externally, computing a correction factor, and writing that value to the FCR. In addition, be aware that the contents of the FCR are not used to directly correct the conversion result. Rather, the correction is a function of the FCR value. This function is linear and two known points can be used as a basis for interpolating intermediate values for the FCR. Consult the Calibration section for more details. The contents of the FCR are in unsigned binary format. This is not affected by the DF bit in the Command Register. TIMING Table XV and Figures 13 through 21 define the basic digital timing characteristics of the ADS1210/11. Figure 13 and the associated timing symbols apply to the XIN input signal. Figures 14 through 20 and associated timing symbols apply to the serial interface signals (SCLK, SDIO, SDOUT, and CS) and their relationship to DRDY. The serial interface is discussed in detail in the Serial Interface section. Figure 21 and the associated timing symbols apply to the maximum DRDY rise and fall times. tXIN t2 XIN t3 Byte 1 OCR15 OCR14 OCR13 OCR12 OCR11 OCR10 OCR9 OCR8 Byte 0 OCR7 OCR6 OCR5 OCR4 OCR3 Least Significant Bit OCR2 OCR1 OCR0 TABLE XIII. Offset Calibration Register. The contents of the OCR are in Two’s Complement format. This is not affected by the DF bit in the Command Register. Full-Scale Calibration Register (FCR) The FCR is a 24-bit register which contains the full-scale correction factor that is applied to the conversion result before it is placed in the Data Output Register (see Table XIV). In most applications, the contents of this register will be the result of either a self-calibration or a system calibration. Most Significant Bit FSR23 FSR22 FSR21 Byte 2 FSR20 Byte 1 FSR15 FSR14 FSR13 FSR12 Byte 0 FSR7 FSR6 FSR5 FSR4 FSR3 FSR11 FSR10 FSR9 FSR8 FSR19 FSR18 FSR17 FSR16 FIGURE 13. XIN Clock Timing. t4 t5 SCLK (Internal) t7 SDIO (as input) SDOUT (or SDlO as output) t9 t6 t8 FIGURE 14. Serial Input/Output Timing, Master Mode. Least Significant Bit FSR2 FSR1 FSR0 SCLK (External) t13 SDIO (as input) SDOUT (or SDlO as output) t15 t10 t11 t12 t14 TABLE XIV. Full-Scale Calibration Register. The FCR is both readable and writable via the serial interface. For applications requiring a more accurate full-scale calibration, multiple calibrations can be performed, each resulting FCR value read, the results averaged, and a more precise calibration value written back to the FCR. FIGURE 15. Serial Input/Output Timing, Slave Mode. ® ADS1210, 1211 22 SYMBOL fXIN tXIN t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12 t13 t14 t15 t16 t17 t18 t19 t20 t21 t22 t23 t24 t25 t26 t27 t28 t29 t30 t31 t32 t33 t34 t35 t36 t37 t38 DESCRIPTION XIN Clock Frequency XIN Clock Period XIN Clock High XIN Clock LOW Internal Serial Clock HIGH Internal Serial Clock LOW Data In Valid to Internal SCLK Falling Edge (Setup) Internal SCLK Falling Edge to Data In Not Valid (Hold) Data Out Valid to Internal SCLK Falling Edge (Setup) Internal SCLK Falling Edge to Data Out Not Valid (Hold) External Serial Clock HIGH External Serial Clock LOW Data In Valid to External SCLK Falling Edge (Setup) External SCLK Falling Edge to Data In Not Valid (Hold) Data Out Valid to External SCLK Falling Edge (Setup) External SCLK Falling Edge to Data Out Not Valid (Hold) Falling Edge of DRDY to First SCLK Rising Edge (Master Mode, CS Tied LOW) Falling Edge of Last SCLK for INSR to Rising Edge of First SCLK for Register Data (Master Mode) Falling Edge of Last SCLK for Register Data to Rising Edge of DRDY (Master Mode) Falling Edge of Last SCLK for INSR to Rising Edge of First SCLK for Register Data (Slave Mode) Falling Edge of Last SCLK for Register Data to Rising Edge of DRDY (Slave Mode) Falling Edge of DRDY to Falling Edge of CS (Master and Slave Mode) Falling Edge of CS to Rising Edge of SCLK (Master Mode) Rising Edge of DRDY to Rising Edge of CS (Master and Slave Mode) Falling Edge of CS to Rising Edge of SCLK (Slave Mode) Falling Edge of Last SCLK for INSR to SDIO Tri-state (Master Mode) SDIO as Output to Rising Edge of First SCLK for Register Data (Master and Slave Modes) Falling Edge of Last SCLK for INSR to SDIO Tri-state (Slave Mode) SDIO Tri-state Time (Master and Slave Modes) Falling Edge of Last SCLK for Register Data to SDIO Tri-State (Master Mode) Falling Edge of Last SCLK for Register Data to SDIO Tri-state (Slave Mode) DRDY Fall Time DRDY Rise Time Minimum DSYNC LOW Time DSYNC Valid HIGH to Falling Edge of XIN (for Exact Synchronization of Multiple Converters only) Falling Edge of XIN to DSYNC Not Valid LOW (for Exact Synchronization of Multiple Converters only) Falling Edge of Last SCLK for Register Data to Rising Edge of First SCLK of next INSR (Slave Mode, CS Tied LOW) Rising Edge of CS to Falling Edge of CS (Slave Mode, Using CS) Falling Edge of DRDY to First SCLK Rising Edge (Slave Mode, CS Tied LOW) MIN 0.5 100 0.4 • tXIN 0.4 • tXIN NOM MAX 10 2000 UNITS MHz ns ns ns tXIN tXIN 40 20 tXIN –25 tXIN 2.5 • tXIN 2.5 • tXIN 40 20 tXIN –40 1.5 • tXIN 6 • tXIN 5 • tXIN 3 • tXIN 5.5 • tXIN 4 • tXIN 0.5 • tXIN 5 • tXIN 10 5.5 • tXIN 2 • tXIN 2 • tXIN 3 • tXIN tXIN tXIN 2 • tXIN 3 • tXIN 30 30 10.5 • tXIN 10 10 20.5 • tXIN 10.5 • tXIN 5.5 • tXIN 4 • tXIN 6 • tXIN 5 • tXIN ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns TABLE XV. Digital Timing Characteristics. ® 23 ADS1210, 1211 t16 DRDY SCLK SDIO IN7 IN1 IN0 t17 t18 INM IN1 IN0 Write Register Data SDIO IN7 IN1 IN0 OUTM OUT1 OUT0 Read Register Data using SDIO SDIO IN7 IN1 IN0 SDOUT OUTM Read Register Data using SDOUT OUT1 OUT0 FIGURE 16. Serial Interface Timing (CS LOW), Master Mode. t38 DRDY t19 SCLK t36 SDIO IN7 IN1 IN0 INM IN1 IN0 IN7 t20 Write Register Data SDIO IN7 IN1 IN0 OUTM OUT1 OUT0 IN7 Read Register Data using SDIO SDIO IN7 IN1 IN0 IN7 SDOUT OUTM Read Register Data using SDOUT OUT1 OUT0 FIGURE 17. Serial Interface Timing (CS LOW), Slave Mode. DRDY t21 CS t22 SCLK SDIO IN7 IN1 IN0 Write Register Data SDIO IN7 IN1 IN0 OUTM OUT1 OUT0 INM IN1 IN0 t17 t23 t18 Read Register Data using SDIO SDIO SDOUT IN7 IN1 IN0 OUTM Read Register Data using SDOUT OUT1 OUT0 DRDY t16 CS SCLK SDIO OUTM OUT1 OUT0 t18 Continuous Read of Data Output Register using SDIO SDOUT OUTM OUT1 OUT0 Continuous Read of Data Output Register using SDOUT FIGURE 18. Serial Interface Timing (Using CS), Master Mode. ® ADS1210, 1211 24 DRDY t21 CS t24 SCLK SDIO IN7 IN1 IN0 Write Register Data SDIO IN7 IN1 IN0 OUTM OUT1 OUT0 IN7 INM IN1 IN0 t19 t23 t24 t20 t37 IN7 Read Register Data Using SDIO SDIO SDOUT IN7 IN1 IN0 OUTM Read Register Data Using SDOUT OUT1 OUT0 IN7 DRDY t16 CS SCLK SDIO OUTM OUT1 OUT0 t20 Continuous Read of Data Output Register using SDIO SDOUT OUTM OUT1 OUT0 Continuous Read of Data Output Register using SDOUT FIGURE 19. Serial Interface Timing (Using CS), Slave Mode. t16 DRDY t21 CS(1) t22 Master Mode SCLK t17 SDIO SCLK Slave Mode SDIO t38 SDIO is an input NOTE: (1) CS is optional. IN7 IN0 t28 t19 SDIO is an output OUT MSB OUT0 t24 IN7 IN6 IN5 IN2 IN1 IN0 t27 t26 OUT M OUT0 t20 t25 t26 t23 t18 t29 t30 FIGURE 20. SDIO Input to Output Transition Timing. t31 DRDY t32 FIGURE 21. DRDY Rise and Fall Time. ® 25 ADS1210, 1211 Synchronizing Multiple Converters A negative going pulse on DSYNC can be used to synchronize multiple ADS1210/11s. This assumes that each ADS1210 is driven from the same master clock and is set to the same Decimation Ratio and Turbo Mode Rate. The affect that this signal has on data output timing in general is discussed in the Serial Interface section. The concern here is what happens if the DSYNC input is completely asynchronous to this master clock. If the DSYNC input rises at a critical point in relation to the master clock input, then some ADS1210/11s may start-up one XIN clock cycle before the others. Thus, the output data will be synchronized, but only to within one XIN clock cycle. For many applications, this will be more than adequate. In these cases, the timing symbols which relate the DSYNC signal to the XIN signal can be ignored. For other multipleconverter applications, this one XIN clock cycle difference could be a problem. These types of applications would include using the DRDY and/or the SCLK output from one ADS1210/11 as the “master” signal for all converters. To ensure exact synchronization to the same XIN edge, the timing relationship between the DSYNC and XIN signals, as shown in Figure 22, must be observed. Figure 23 shows a simple circuit which can be used to clock multiple ADS1210/11s from one ADS1210/11, as well as to ensure that an asynchronous DSYNC signal will exactly synchronize all the converters. SERIAL INTERFACE The ADS1210/11 includes a flexible serial interface which can be connected to microcontrollers and digital signal processors in a variety of ways. Along with this flexibility, there is also a good deal of complexity. This section describes the trade-offs between the different types of interfacing methods in a top-down approach—starting with the overall flow and control of serial data, moving to specific interface examples, and then providing information on various issues related to the serial interface. Multiple Instructions The general timing diagrams which appear throughout this data sheet show serial communication to and from the ADS1210/11 occurring during the DRDY LOW period (see Figures 4 through 10 and Figure 36). This communication represents one instruction that is executed by the ADS1210/ 11, resulting in a single read or write of register data. However, more than one instruction can be executed by the ADS1210/11 during any given conversion period (see Figure 24). Note that DRDY remains HIGH during the subsequent instructions. There are several important restrictions on how and when multiple instructions can be issued during any one conversion period. Internal Update of DOR 12 • tXIN DRDY t34 XIN t35 t33 DSYNC Serial I/O FIGURE 24. Timing of Data Output Register Update. The first restriction is that the converter must be in the Slave Mode. There is no provision for multiple instructions when the ADS1210/11 is operating in the Master Mode. The second is that some instructions will produce invalid results if started at the end of one conversion period and carried into the start of the next conversion period. FIGURE 22. DSYNC to XIN Timing for Synchronizing Mutliple ADS1210/11s. Asynchronous DSYNC Strobe 1/2 74AHC74 D CLK Q Q 1/6 74AHC04 C1 12pF XTAL C2 12pF DSYNC XIN XOUT DGND SDOUT SDIO SCLK DVDD DSYNC XIN XOUT DGND SDOUT SDIO SCLK DVDD DSYNC XIN XOUT DGND SDOUT SDIO SCLK DVDD DGND ADS1210/11 ADS1210/11 ADS1210/11 FIGURE 23. Exactly Synchronizing Multiple ADS1210/11s to an Asynchronous DSYNC Signal. ® ADS1210, 1211 26 For example, Figure 24 shows that just prior to the DRDY signal going LOW, the internal Data Output Register (DOR) is updated. This update involves the Offset Calibration Register (OCR) and the Full-Scale Register (FSR). If the OCR or FSR are being written, their final value may not be correct, and the result placed into the DOR will certainly not be valid. Problems can also arise if certain bits of the Command Register are being changed. Note that reading the Data Output Register is an exception. If the DOR is being read when the internal update is initiated, the update is blocked. The old output data will remain in the DOR and the new data will be lost. The old data will remain valid until the read operation has completed. In general, multiple instructions may be issued, but the last one in any conversion period should be complete within 12 • XIN clock periods of the next DRDY LOW time. In this usage, “complete” refers to the point where DRDY rises in Figures 17 and 19 (in the Timing Section). Consult Figures 25 and 26 for the flow of serial data during any one conversion period. Start Reading Start Writing ADS1210/11 drives DRDY LOW ADS1210/11 drives DRDY LOW CS state HIGH LOW CS state HIGH LOW CS state HIGH LOW No ADS1210/11 generates 8 serial clock cycles and receives Instruction Register data via SDIO ADS1210/11 generates 8 serial clock cycles and receives Instruction Register data via SDIO Continuous Read Mode? Yes ADS1210/11 generates n serial clock cycles and receives specified register data via SDIO Use SDIO for output? Yes No SDOUT becomes active from tri-state SDIO input to output transition ADS1210/11 drives DRDY HIGH End ADS1210/11 generates n serial clock cycles and transmits specified register data via SDOUT ADS1210/11 generates n serial clock cycles and transmits specified register data via SDIO SDOUT returns to tri-state condition SDIO transitions to tri-state condition ADS1210/11 drives DRDY HIGH End FIGURE 25. Flowchart for Writing and Reading Register Data, Master Mode. ® 27 ADS1210, 1211 Start Reading Start Writing From Read Flowchart ADS1210/11 drives DRDY LOW To Write Flowchart ADS1210/11 drives DRDY LOW CS taken HIGH for 10.5 t XIN periods minimum (see text if CS tied LOW). LOW CS state HIGH CS taken HIGH for 10.5 t XIN periods minimum (see text if CS tied LOW). CS state HIGH LOW LOW External device generates 8 serial clock cycles and transmits instruction register data via SDIO CS state HIGH Continuous Read Mode? No Yes CS state LOW HIGH External device generates 8 serial clock cycles transmits and receives instruction register data via SDIO External device generates n serial clock cycles and transmits specified register data via SDIO Use SDIO for output? Yes No ADS1210/11 drives DRDY HIGH SDOUT becomes active SDIO input to output transition Yes More Instructions? See text for restrictions Is Next Instruction a Read? No External device generates n serial clock cycles and transmits specified register data via SDOUT External device generates n serial clock cycles and receives specified register data via SDIO No Yes SDOUT returns to tri-state condition SDIO transitions to tri-state condition End To Read Flowchart ADS1210/11 drives DRDY HIGH No More Instructions? No End Yes See text for restrictions Is Next Instruction a Write? Yes To Write Flowchart FIGURE 26. Flowchart for Writing and Reading Register Data, Slave Mode. ® ADS1210, 1211 28 Using CS and Continuous Read Mode The serial interface may make use of the CS signal, or this input may simply be tied LOW. There are several issues associated with choosing to do one or the other. The CS signal does not directly control the tri-state condition of the SDOUT or SDIO output. These signals are normally in the tri-state condition. They only become active when serial data is being transmitted from the ADS1210/11. If the ADS1210/11 is in the middle of a serial transfer and SDOUT or SDIO is an output, taking CS HIGH will not tri-state the output signal. If there are multiple serial peripherals utilizing the same serial I/O lines and communication may occur with any peripheral at any time, then the CS signal must be used. The ADS1210/11 may be in the Master Mode or the Slave Mode. In the Master Mode, the CS signal is used to hold-off serial communication with a “ready” (DRDY LOW) ADS1210/11 until the main controller can accommodate the communication. In the Slave Mode, the CS signal is used to enable communication with the ADS1210/11. The CS input has another use. If the CS state is left LOW after a read of the Data Output Register has been performed, then the next time that DRDY goes LOW, the ADS1210/11 Instruction Register will not be entered. Instead, the Instruction Register contents will be re-used, and the new contents of the Data Output Register, or some part thereof, will be transmitted. This will occur as long as CS is LOW and not toggled. This mode of operation is called the Continuous Read Mode and is shown in the read flowcharts of Figures 25 and 26. It is also shown in the Timing Diagrams of Figures 18 and 19 in the Timing section. Note that once CS has been taken HIGH, the Continuous Read Mode will be enabled (but not entered) and can never be disabled. The mode is actually entered and exited as described above. Power-On Conditions for SDIO Even if the SDIO connection will be used only for input, there is one important item to consider regarding SDIO. This only applies when the ADS1210/11 is in the Master Mode and CS will be tied LOW. At power-up, the serial I/O lines of most microcontrollers and digital signal processors will be in a tri-state condition, or they will be configured as inputs. When power is applied to the ADS1210/11, it will begin operating as defined by the default condition of the Command Register (see Table X in the System Configuration section). This condition defines SDIO as the data output pin. Since the ADS1210/11 is in the Master Mode and CS is tied LOW, the serial clock will run whenever DRDY is LOW and an instruction will be entered and executed. If the SDIO line is HIGH, as it might be with an active pull-up, then the instruction is a read operation and SDIO will become an output every DRDY LOW period—for 32 serial clock cycles. When the serial port on the main controller is enabled, signal contention could result. The recommended solution to this problem is to actively pull SDIO LOW. If SDIO is LOW when the ADS1210/11 enters the instruction byte, then the resulting instruction is a write of one byte of data to the Data Output Register, which results in no internal operation. If the SDIO signal cannot be actively pulled LOW, then another possibility is to time the initialization of the controller’s serial port such that it becomes active between adjacent DRDY LOW periods. The default configuration for the ADS1210/11 produces a data rate of 814Hz—a conversion period of 1.2ms. This time should be more than adequate for most microcontrollers and DSPs to monitor DRDY and initialize the serial port at the appropriate time. Master Mode The Master Mode is active when the MODE input is HIGH. All serial clock cycles will be produced by the ADS1210/11 in this mode, and the SCLK pin is configured as an output. The frequency of the serial clock will be one-half of the XIN frequency. Multiple instructions cannot be issued during a single conversion period in this mode—only one instruction per conversion cycle is possible. The Master Mode will be difficult for some microcontrollers, particularly when the XIN input frequency is greater than a few MHz, as the serial clock may exceed the microcontroller’s maximum serial clock frequency. For the majority of digital signal processors, this will be much less of a concern. In addition, if SDIO is being used as an input and an output, then the transition time from input to output may be a concern. This will be true for both microcontrollers and DSPs. See Figure 20 in the Timing section. Note that if CS is tied LOW, there are special considerations regarding SDIO as outlined previously in this section. Also note that if CS is being used to control the flow of data from the ADS1210/11 and it remains HIGH for one or more conversion periods, the ADS1210/11 will operate properly. However, the result in the Data Output Register will be lost when it is overwritten by each new result. Just prior to this update, DRDY will be forced HIGH and will return LOW after the update. Slave Mode Most systems will use the ADS1210/11 in the Slave Mode. This mode allows multiple instructions to be issued per conversion period as well as allowing the main controller to set the serial clock frequency and pace the serial data transfer. The ADS1210/11 is in the Slave Mode when the MODE input is LOW. There are several important items regarding the serial clock for this mode of operation. The maximum serial clock frequency cannot exceed the ADS1210/11 XIN frequency divided by 5 (see Figure 15 in the Timing section). When using SDIO as the serial output, the falling edge of the last serial clock cycle of the instruction byte will cause the SDIO pin to begin its transition from input to output. Between three and four XIN cycles after this falling edge, the SDIO pin will become an output. This transition may be too fast for some microcontrollers and digital signal processors. ® 29 ADS1210, 1211 If a serial communication does not occur during any conversion period, the ADS1210/11 will continue to operate properly. However, the results in the Data Output Register will be lost when they are overwritten by the new result at the start of the next conversion period. Just prior to this update, DRDY will be forced HIGH and will return LOW after the update. Making Use of DSYNC The DSYNC input pin and the DSYNC write bit in the Command Register reset the current modulator count to zero. This causes the current conversion cycle to proceed as normal, but all modulator outputs from the last data output to the point where DSYNC is asserted are discarded. Note that the previous two data outputs are still present in the ADS1210/11 internal memory. Both will be used to compute the next conversion result, and the most recent one will be used to compute the result two conversions later. DSYNC does not reset the internal data to zero. There are two main uses of DSYNC. In the first case, DSYNC allows for synchronization of multiple converters. In regards to the DSYNC input pin, this case was discussed under “Synchronizing Multiple Converters” in the Timing section. In regards to the DSYNC bit, it will be difficult to set all of the converter’s DSYNC bits at the same time unless all of the converters are in the Slave Mode and the same instruction can be sent to all of the converters at the same time. The second use of DSYNC is to reset the modulator count to zero in order to obtain valid data as quickly as possible. For example, if the input channel is changed on the ADS1211, the current conversion cycle will be a mix of the old channel and the new channels. Thus, four conversions are needed in order to ensure valid data. However, if the channel is changed and then DSYNC is used to reset the modulator count, the modulator data at the end of the current conversion cycle will be entirely from the new channel. After two additional conversion cycles, the output data will be completely valid. Note that the conversion cycle in which DSYNC is used will be slightly longer than normal. Its length will depend on when DSYNC was set. Reset, Power-On Reset, and Brown-Out The ADS1210/11 contains an internal power-on reset circuit. If the power supply ramp rate is greater than 50mV/ms, this circuit will be adequate to ensure that the device powers up correctly. (Due to oscillator settling considerations, commu- nication to and from the ADS1210/11 should not occur for at least 25ms after power is stable.) If this requirement cannot be met or if the circuit has brown-out considerations, the timing diagram of Figure 27 can be used to reset the ADS1210/11. This timing applies only when the ADS1210/11 is in the Slave Mode and accomplishes the reset by controlling the duty cycle of the SCLK input. In general, a reset is required after power-up, after a brown-out has been detected, or when a watchdog timer event has occured. If the ADS1210/11 is in the Master Mode, a reset of the device is not possible. If the power supply does not meet the minimum ramp rate requirement, or brown-out is of concern, low on-resistance MOSFETs or equivalent should be used to control power to the ADS1210/11. When powered down, the device should be left unpowered for at least 300ms before power is reapplied. An alternate method would be to control the MODE pin and temporarily place the ADS1210/11 in the Slave Mode while a reset is initiated as shown in Figure 27. Two-Wire Interface For a two-wire interface, the Master Mode of operation may be preferable. In this mode, serial communication occurs only when data is ready, informing the main controller as to the status of the ADS1210/11. The disadvantages are that the ADS1210/11 must have a dedicated serial port on the main controller, only one instruction can be issued per data ready period, and the serial clock may define the maximum clock frequency of the converter. In the Slave Mode, the main controller must read and write to the ADS1210/11 “blindly”. Writes to the internal registers, such as the Command Register or Offset Calibration Register, might occur during an update of the Data Output Register. This can result in invalid data in the DOR. A twowire interface can be used if the main controller can read and/or write to the converter, either much slower or much faster that the data rate. For example, if much faster, the main controller can use the DRDY bit to determine when data is becoming valid (polling it multiple times during one conversion cycle). Thus, the controller obtains some idea of when to write to the internal register. If much slower, then reads of the DOR might always return valid data (multiple conversions have occurred since the last read of the DOR or since any write of the internal registers). Reset Occurs at Falling Edge t2 SCLK t1 t3 t4 t2 t1: > 256 • tXIN < 400 • tXIN t2: > 5 • tXIN t3: > 512 • tXIN < 900 • tXIN t4: ≥ 1024 • tXIN < 1200 • tXIN FIGURE 27. Resetting the ADS1210/11 (Slave Mode only). ® ADS1210, 1211 30 Three-Wire Interface Figure 28 shows a three-wire interface with a 8xC32 microprocessor. Note that the Slave Mode is being selected and the SDIO pin is being used for input and output. Figure 29 shows a different type of three-wire interface with a 8xC51 microprocessor. Here, the Master Mode is used. The interface signals consist of SDOUT, SDIO, and SCLK. P1.0 P1.1 P1.2 AVDD P1.3 P1.4 AINP AINN AGND AGND DVDD VBIAS CS ADS1210 REFIN REFOUT AVDD MODE DRDY DGND RXD TXD INT0 INT1 DVDD R1 10kΩ T0 T1 DGND WR C1 27pF XTAL Q Q D CLK Q Q D CLK C2 27pF RD X2 X1 VSS AGND 1.0µF P1.5 P1.6 P1.7 RESET 8xC32 DSYNC XIN XOUT DGND SDOUT SDIO SCLK DVDD 1/2 74HC74 1/2 74HC74 FIGURE 28. Three-Wire Interface with a 8xC32 Microprocessor. P1.0 P1.1 P1.2 AVDD AINP AINN AGND AGND DVDD C1 12pF XTAL C2 12pF DGND VBIAS CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD R1 10kΩ DVDD P1.3 P1.4 1.0µF AGND P1.5 P1.6 P1.7 8xC51 VCC P0.0 P0.1 P0.2 P0.3 P0.4 P0.5 P0.6 DSYNC XIN XOUT DGND DGND FIGURE 29. Three-Wire Interface with a 8xC51 Microprocessor. ® 31 ADS1210, 1211 Four-wire Interface Figure 30 shows a four-wire interface with a 8xC32 microprocessor. Again, the Slave Mode is being used. Multi-wire Interface Figures 31 and 32 show multi-wire interfaces with a 8xC51 or 68HC11 microprocessor. In these interfaces, the mode of the ADS1210/11 is actually controlled dynamically. This could be extremely useful when the ADS1210/11 is to be used in a wide variety of ways. For example, it might be desirable to have the ADS1210/11 produce data at a steady rate and to have the converter operating in the Continuous Read Mode. But for system calibration, the Slave Mode might be preferred because multiple instructions can be issued per conversion period. Note that the MODE input should not be changed in the middle of a serial transfer. This could result in misoperation of the device. A Master/Slave Mode change will not affect the output data. Note that the XIN input can also be controlled. It is possible with some microcontrollers and digital signal processors to produce a continuous serial clock, which could be connected to the XIN input. The frequency of the clock is often settable over some range. Thus, the power dissipation of the ADS1210/11 could be dynamically varied by changing both the Turbo Mode and XIN input-trading off conversion speed and resolution for power consumption. I/O Recovery If serial communication stops during an instruction or data transfer for longer than 4 • tDATA, the ADS1210/11 will reset its serial interface. This will not affect the internal registers. The main controller must not continue the transfer after this event, but must restart the transfer from the beginning. This feature is very useful if the main controller can be reset at any point. After reset, simply wait 8 • tDATA before starting serial communication. P1.0 P1.1 P1.2 AVDD P1.3 P1.4 AINP AINN AGND AGND DVDD VBIAS CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD DVDD R1 10kΩ C1 27pF DGND RXD TXD INT0 INT1 WR RD X2 X1 Q Q D CLK Q Q D CLK C2 27pF XTAL VSS AGND 1.0µF P1.5 P1.6 P1.7 RESET 8xC32 DSYNC XIN XOUT DGND DGND 1/2 74HC74 1/2 74HC74 FIGURE 30. Four-Wire Interface with a 8xC32 Microprocessor. AVDD AINP AINN AGND AGND C1 12pF XTAL C2 12pF DGND VBIAS CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD DVDD R1 10kΩ R2 10kΩ AGND P1.0 1.0µF P1.1 P1.2 P1.3 P1.4 P1.5 P1.6 P1.7 8xC51 VCC P0.0 P0.1 P0.2 P0.3 P0.4 P0.5 P0.6 DSYNC XIN XOUT DGND DGND FIGURE 31. Full Interface with a 8xC51 Microprocessor. ® ADS1210, 1211 32 PB7 PB6 PB5 PB4 PB3 PB2 PB1 PB0 PE0 PE1 PE2 68HC11 XIRQ RESET PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0 XTAL C1 12pF XTAL C2 12pF AGND AINP AINN AGND VBIAS CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD DVDD R2 10kΩ R1 10kΩ AGND 1.0µF AVDD DSYNC XIN XOUT DGND DGND FIGURE 32. Full Interface with a 68HC11 Microprocessor. VDD2 DRDY DGND R/T2A R/T2B R/T1B D2A D1A VSA AINP AINN AGND AGND VDD1 C1 12pF XTAL C2 12pF DGND VBIAS CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO 1.0µF AGND VDD1 DGND VDD1 VDD1 SDOUT VDD2 GND VDD2 GND SDIN DGND DSYNC XIN XOUT DGND R1 100Ω R/T2A R/T2B R/T1B D2A SCLK DVDD DGND R/T1A D1A VSA ISO150 VSB VDD1 SCLK DGND GND VDD2 FIGURE 33. Isolated Four-Wire Interface. Isolation The serial interface of the ADS1210/11 provides for simple isolation methods. An example of an isolated four-wire interface is shown in Figure 33. The ISO150 is used to transmit the digital signals over the isolation barrier. 33 In addition, the digital outputs of the ADS1210/11 can, in some cases, drive opto-isolators directly. Figures 34 and 35 show the voltage of the SDOUT pin versus source or sink current under worst case conditions. Worst-case conditions for source current occur when the analog input differential ® ADS1210, 1211 D1B GB D2B GA D1B GB AVDD R/T1A ISO150 VSB D2B GA SOURCE CURRENT 30 25 20 AIN3N AIN2P AIN3P +5V AIN4N AIN4P REFIN REFOUT ADS1211U, P AVDD MODE DRDY SDOUT SDIO SCLK DVDD +5V VOH P1 2kΩ 0V +5V VOH AVDD +5V 1.0µF REF1004 +2.5V R1 49.9kΩ AIN2N AIN1P 25°C 85°C –40°C +5V IOUT (mA) AIN1N AGND 15 +5V VBIAS CS DSYNC XIN XTAL C2 12pF DGND XOUT DGND 10 5 0 0 1 2 VOH (V) 3 4 5 DGND C1 12pF FIGURE 34. Source Current vs VOH for SDOUT Under Worst-Case Conditions. SINK CURRENT 30 25 20 –40°C 25°C 85°C 0V AIN3N AIN2P AIN2N AIN1P AIN1N AGND VBIAS ADS1211U, P AIN3P +5V AIN4N AIN4P REFIN REFOUT AVDD MODE DRDY SDOUT SDIO SCLK DVDD VOL VOL P1 2kΩ +5V +5V 0V AVDD +5V 1.0µF REF1004 +2.5V R1 49.9kΩ IOUT (mA) 15 10 5 0 0 1 2 VOL (V) 3 4 5 C2 12pF DGND +5V C1 12pF XTAL CS DSYNC XIN XOUT DGND DGND FIGURE 35. Sink Current vs VOL for SDOUT Under Worst-Case Conditions. voltage is 5V and the output format is Offset Binary (FFFFFFH). For sink current, the worst-case condition occurs when the analog input differential voltage is 0V and the output format is Two’s Complement (000000H). Note that SDOUT is tri-stated for the majority of the conversion period and the opto-isolator connection must take this into account. Synchronization of Multiple Converters The DSYNC input is used to synchronize the output data of multiple ADS1210/11s. Synchronization involves configuring each ADS1210/11 to the same Decimation Ratio and Turbo Mode setting, and providing a common signal to the XIN inputs. Then, the DSYNC signal is pulsed LOW (see Figure 22 in the Timing section). This results in an internal reset of the modulator count for the current conversion. Thus, all the converters start counting from zero at the same time, producing a DRDY LOW signal at approximately the same point (see Figure 36). Note that an asynchronous DSYNC input may cause multiple converters to be different from one another by one XIN clock cycle. This should not be a concern for most applications. However, the Timing section contains information on exactly synchronizing multiple converters to the same XIN clock cycle. tDATA DRDY A tDATA DRDY B tDATA DRDY C DSYNC tDATA FIGURE 36. Affect of Synchronization on Output Data Timing. ® ADS1210, 1211 34 LAYOUT POWER SUPPLIES The ADS1210/11 requires the digital supply (DVDD) to be no greater than the analog supply (AVDD) +0.3V. In the majority of systems, this means that the analog supply must come up first, followed by the digital supply. Failure to observe this condition could cause permanent damage to the ADS1210/11. Inputs to the ADS1210/11, such as SDIO, AIN, or REFIN, should not be present before the analog and digital supplies are on. Violating this condition could cause latch-up. If these signals are present before the supplies are on, series resistors should be used to limit the input current (see the Analog Input and VBIAS sections of this data sheet for more details concerning these inputs). The best scheme is to power the analog section of the design and AVDD of the ADS1210/11 from one +5V supply and the digital section (and DVDD) from a separate +5V supply. The analog supply should come up first. This will ensure that AIN and REFIN do not exceed AVDD and that the digital inputs are present only after AVDD has been established, and that they do not exceed DVDD. The analog supply should be well regulated and low noise. For designs requiring very high resolution from the ADS1210/ 11, power supply rejection will be a concern. See the PSRR vs Frequency curve in the Typical Performance Curves section of this data sheet for more information. The requirements for the digital supply are not as strict. However, high frequency noise on DVDD can capacitively couple into the analog portion of the ADS1210/11. This noise can originate from switching power supplies, very fast microprocessors or digital signal processors. For either supply, high frequency noise will generally be rejected by the digital filter except at interger multiplies of fMOD. Just below and above these frequencies, noise will alias back into the passband of the digital filter, affecting the conversion result. If one supply must be used to power the ADS1210/11, the AVDD supply should be used to power DVDD. This connection can be made via a 10Ω resistor which, along with the decoupling capacitors, will provide some filtering between DVDD and AVDD. In some systems, a direct connection can be made. Experimentation may be the best way to determine the appropriate connection between AVDD and DVDD. GROUNDING The analog and digital sections of the design should be carefully and cleanly partitioned. Each section should have its own ground plane with no overlap between them. AGND should be connected to the analog ground plane as well as all other analog grounds. DGND should be connected to the digital ground plane and all digital signals referenced to this plane. The ADS1210/11 pinout is such that the converter is cleanly separated into an analog and digital portion. This should allow simple layout of the analog and digital sections of the design. For a single converter system, AGND and DGND of the ADS1210/11 should be connected together, underneath the converter. Do not join the ground planes, but connect the two with a moderate signal trace. For multiple converters, connect the two ground planes at one location as central to all of the converters as possible. In some cases, experimentation may be required to find the best point to connect the two planes together. The printed circuit board can be designed to provide different analog/digital ground connections via short jumpers. The initial prototype can be used to establish which connection works best. DECOUPLING Good decoupling practices should be used for the ADS1210/ 11 and for all components in the design. All decoupling capacitors, but specifically the 0.1µF ceramic capacitors, should be placed as close as possible to the pin being decoupled. A 1µF to 10µF capacitor, in parallel with a 0.1µF ceramic capacitor, should be used to decouple AVDD to AGND. At a minimum, a 0.1µF ceramic capacitor should be used to decouple DVDD to DGND, as well as for the digital supply on each digital component. SYSTEM CONSIDERATIONS The recommendations for power supplies and grounding will change depending on the requirements and specific design of the overall system. Achieving 20 bits or more of effective resolution is a great deal more difficult than achieving 12 bits. In general, a system can be broken up into four different stages: Analog Processing Analog Portion of the ADS1210/11 Digital Portion of the ADS1210/11 Digital Processing For the simplest system consisting of minimal analog signal processing (basic filtering and gain), a self-contained microcontroller, and one clock source, high-resolution could be achieved by powering all components by a common power supply. In addition, all components could share a common ground plane. Thus, there would be no distinctions between “analog” and “digital” power and ground. The layout should still include a power plane, a ground plane, and careful decoupling. In a more extreme case, the design could include: multiple ADS1210/11s; extensive analog signal processing; one or more microcontrollers, digital signal processors, or microprocessors; many different clock sources; and interconnections to various other systems. High resolution will be very difficult to achieve for this design. The approach would be to break the system into as many different parts as possible. For example, each ADS1210/11 may have its own “analog” processing front end, its own analog power and ground (possibly shared with the analog front end), and its own “digital” power and ground. The converter’s “digital” power and ground would be separate from the power and ground for the system’s processors, RAM, ROM, and “glue” logic. ® 35 ADS1210, 1211 APPLICATIONS The ADS1210/11 can be used in a broad range of data acquisition tasks. The following application diagrams show the ADS1210 and/or ADS1211 being used for bridge transducer measurements, temperature measurement, and 4-20mA receiver applications. 1/2 OPA1013 AGND 3kΩ AINP AINN AGND AGND DVDD C1 12pF XTAL C2 12pF DGND AGND VBIAS CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD DVDD AGND 1.0µF AVDD DSYNC XIN XOUT DGND DGND FIGURE 37. Bridge Transducer Interface with Voltage Excitation. R1 6kΩ +In 10kΩ RG 3 1 5 INA118 AINP AINN AGND AGND VBIAS DVDD CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD DVDD DGND AVDD AGND 8 –In 2 6 1.0µF 8 100µA 7 6 100µA I 5 REF200 O C1 12pF DSYNC XIN XTAL XOUT DGND A 1 B 2 3 4 C DGND C2 12pF DGND AGND FIGURE 38. Bridge Transducer Interface with Current Excitation. ® ADS1210, 1211 36 REF200 100µA 100µA A B +In RG R1 100Ω R2 100Ω –In 3 1 7 5 INA118 6 AINP AINN 4 AGND AGND DVDD AGND VBIAS CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD DVDD DGND AVDD AGND 1.0µF 8 2 R3 14kΩ C1 12pF XTAL C2 12pF DGND DSYNC XIN AGND DGND XOUT DGND FIGURE 39. PT100 Interface. +15V +In 3 4–20mA –In 1 –15V C1 12pF XTAL C2 12pF DGND 5 AGND DVDD CT 2 15 RCV420 13 14 AINP AINN AGND VBIAS CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD DVDD DGND AVDD AGND 1.0µF DSYNC XIN XOUT DGND DGND FIGURE 40. Complete 4-20mA Receiver. 3 1 RG –In Termination R1 10kΩ 8 2 INA128 4 +In 7 5 6 AINP AINN AGND AGND DVDD C1 12pF XTAL C2 12pF DGND VBIAS CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD DVDD DGND +5V AGND 1.0µF AGND DSYNC XIN XOUT DGND DGND FIGURE 41. Single Supply, High Accuracy Thermocouple. ® 37 ADS1210, 1211 +In 3 1 7 5 INA128 4 AGND –5V DVDD C1 12pF XTAL C2 12pF DGND 6 AINP AINN AGND VBIAS CS REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD DVDD DGND +5V AGND 1.0µF RG –In R1 10kΩ 8 2 AGND DSYNC XIN XOUT DGND DGND FIGURE 42. Dual Supply, High Accuracy Thermocouple. +In 3 1 7 5 INA118 6 AGND AIN3N AIN2P AIN2N AIN1P AGND AIN1N AGND AGND ADS1211U, P AIN3P AIN4N AIN4P REFIN REFOUT AVDD MODE DRDY DGND DSYNC XIN XTAL C2 12pF DGND XOUT DGND SDOUT SDIO SCLK DVDD DVDD +5V AGND AGND 1.0µF RG –In R1 10kΩ 8 2 4 1N4148 AGND R2 13kΩ C1 12pF VBIAS DVDD CS DGND FIGURE 43. Single Supply, High Accuracy Thermocouple Interface with Cold Junction Compensation. ® ADS1210, 1211 38 +In 3 1 7 5 INA118 6 AIN3N AIN2P AIN2N AIN1P AIN1N AIN3P AIN4N AIN4P AGND REFIN REFOUT ADS1211U, P AVDD MODE DRDY DGND DSYNC XIN XTAL C2 12pF DGND XOUT DGND SDOUT SDIO SCLK DVDD DVDD +5V AGND 1.0µF RG –In 8 2 4 –5V R1 10kΩ AGND AGND AGND VBIAS DVDD C1 12pF CS 1N4148 AGND R2 13kΩ DGND FIGURE 44. Dual Supply, High Accuracy Thermocouple Interface with Cold Junction Compensation. R1 6kΩ –In 10kΩ +In AINP AINN AGND REFIN REFOUT AVDD MODE ADS1210 DRDY SDOUT SDIO SCLK DVDD DVDD AVDD AGND 1.0µF AVDD 8 100µA 7 6 100µA I 5 REF200 O DVDD C1 12pF XTAL A 1 B 2 3 4 C DGND C2 12pF AGND VBIAS CS DSYNC XIN XOUT DGND DGND AGND FIGURE 45. Low Cost Bridge Transducer Interface with Current Excitation. ® 39 ADS1210, 1211 TOPIC INDEX TOPIC PAGE 1 1 1 2 TOPIC PAGE FEATURES ..................................................................................... APPLICATIONS ............................................................................. DESCRIPTION ............................................................................... SPECIFICATIONS .......................................................................... ANALOG OPERATION ................................................................. 17 ANALOG INPUT ....................................................................................... 17 REFERENCE INPUT ................................................................................ 17 REFERENCE OUTPUT ............................................................................ 17 VBIAS ..................................................................................................................................................... 18 ABSOLUTE MAXIMUM RATINGS ............................................................. 3 ELECTROSTATIC DISCHARGE SENSITIVITY ........................................ 3 PACKAGE INFORMATION ........................................................................ 3 ORDERING INFORMATION ...................................................................... 3 ADS1210 SIMPLIFIED BLOCK DIAGRAM ................................................ 4 ADS1210 PIN CONFIGURATION .............................................................. 4 ADS1210 PIN DEFINITIONS ..................................................................... 4 ADS1211 SIMPLIFIED BLOCK DIAGRAM ................................................ 5 ADS1211P and ADS1211U PIN CONFIGURATION ................................. 5 ADS1211P and ADS1211U PIN DEFINITIONS ........................................ 5 ADS1211E PIN CONFIGURATION ........................................................... 6 ADS1211E PIN DEFINITIONS ................................................................... 6 DIGITAL OPERATION .................................................................. 18 SYSTEM CONFIGURATION .................................................................... 18 Instruction Register (INSR) ................................................................... 19 Command Register (CMR) .................................................................... 19 Data Output Register (DOR) ................................................................. 21 Offset Calibration Register (OCR) ........................................................ 22 Full-Scale Calibration Register (FCR) ................................................... 22 TIMING ..................................................................................................... 22 Synchronizing Multiple Converters ........................................................ 26 SERIAL INTERFACE ............................................................................... 26 Multiple Instructions ............................................................................... 26 Using CS and Continuous Read Mode ................................................ 29 Power-On Conditions for SDIO ............................................................. 29 Master Mode .......................................................................................... 29 Slave Mode ............................................................................................ 29 Making Use of DSYNC ......................................................................... 30 Reset, Power-On Reset, and Brown-Out ............................................. 30 Two-Wire Interface ................................................................................ 30 Three-Wire Interface .............................................................................. 30 Four-Wire Interface ................................................................................ 30 Multi-Wire Interface ............................................................................... 32 I/O Recovery .......................................................................................... 32 Isolation ................................................................................................. 33 Synchronization of Multiple Converters ................................................ 34 TYPICAL PERFORMANCE CURVES ........................................... 7 THEORY OF OPERATION ............................................................ 9 DEFINITION OF TERMS ......................................................................... 10 DIGITAL FILTER ...................................................................................... 11 Filter Equation ....................................................................................... 12 Filter Settling .......................................................................................... 12 TURBO MODE ......................................................................................... 12 PROGRAMMABLE GAIN AMPLIFIER ..................................................... 13 SOFTWARE GAIN ................................................................................... 13 CALIBRATION .......................................................................................... 13 Self-Calibration ...................................................................................... 14 System Offset Calibration ..................................................................... 14 System Full-Scale Calibration ............................................................... 14 Pseudo System Calibration ................................................................... 15 Background Calibration ......................................................................... 15 System Calibration Offset and Full-Scale Calibration Limits ................ 16 SLEEP MODE .......................................................................................... 16 LAYOUT ........................................................................................ 35 POWER SUPPLIES ................................................................................. 35 GROUNDING ............................................................................................ 35 DECOUPLING .......................................................................................... 35 SYSTEM CONSIDERATIONS ................................................................. 35 APPLICATIONS ............................................................................ 36 ® ADS1210, 1211 40 FIGURE INDEX FIGURE Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 Figure 27 Figure 28 Figure 29 Figure 30 Figure 31 Figure 32 Figure 33 Figure 34 Figure 35 Figure 36 Figure 37 Figure 38 Figure 39 Figure 40 Figure 41 Figure 42 Figure 43 Figure 44 Figure 45 TABLE INDEX PAGE TABLE Table I Table II Table III Table IV Table V Table VI Table VII Table VIII Table IX Table X Table XI Table XII Table XIII Table XIV Table XV TITLE TITLE PAGE Normalized Digital Filter Response ......................................... 11 Digital Filter Response at a Data Rate of 50Hz ..................... 11 Digital Filter Response at a Data Rate of 60Hz ..................... 11 Asynchronous ADS1210/11 Analog Input Voltage Step or ADS1211 Channel Change to Fully Settled Output Data ...... 12 Self-Calibration Timing ............................................................ 14 System Offset Calibration Timing ........................................... 14 System Full-Scale Calibration ................................................. 14 Pseudo System Calibration Timing ......................................... 15 Background Calibration ........................................................... 15 Sleep Mode to Normal Mode Timing ...................................... 17 Analog Input Structure ............................................................. 17 ±10V Input Configuration Using VBIAS .................................................... 18 XIN Clock Timing ...................................................................... 22 Serial Input/Output Timing, Master Mode ............................... 22 Serial Input/Output Timing, Slave Mode ................................. 22 Serial Interface Timing (CS LOW), Master Mode ................... 24 Serial Interface Timing (CS LOW), Slave Mode ..................... 24 Serial Interface Timing (Using CS), Master Mode .................. 24 Serial Interface Timing (Using CS), Slave Mode .................... 25 SDIO Input to Output Transition Timing ................................. 25 DRDY Rise and Fall Time ....................................................... 25 DSYNC to XIN Timing for Synchronizing Multiple ADS1210/11s ........................................................................... 26 Exactly Synchronizing Multiple ADS1210/11s to Asynchronous DSYNC Signal ............................................. 26 Timing of Data Output Register Update ................................. 26 Flowchart for Writing and Reading Register Data, Master Mode 27 Flowchart for Writing and Reading Register Data, Slave Mode .. 28 Resetting the ADS1210/11 (Slave Mode Only) ...................... 30 Three-Wire Interface with an 8xC32 Microprocessor ............. 31 Three-Wire Interface with an 8xC51 Microprocessor ............. 31 Four-Wire Interface with an 8xC32 Microprocessor ............... 32 Full Interface with an 8xC51 Microprocessor ......................... 32 Full Interface with a 68HC11 Microprocessor ........................ 33 Isolated Four-Wire Interface .................................................... 33 Source Current vs VOH for SDOUT Under Worst-Case Conditions ............................................................ 34 Sink Current vs VOL for SDOUT Under Worst-Case Conditions ............................................................ 34 Affect of Synchronization on Output Data Timing .................. 34 Bridge Transducer Interface with Voltage Excitation .............. 36 Bridge Transducer Interface with Current Excitation .............. 36 PT100 Interface ....................................................................... 37 Complete 4-20mA Receiver .................................................... 37 Single Supply, High Accuracy Thermocouple ......................... 37 Dual Supply, High Accuracy Thermocouple ........................... 38 Single Supply, High Accuracy Thermocouple Interface with Cold Junction Compensation ........................................... 38 Dual Supply, High Accuracy Thermocouple Interface with Cold Junction Compensation ........................................... 39 Low Cost Bridge Transducer Interface with Current Excitation ..... 39 Full-Scale Range vs PGA Setting ............................................. 9 Available PGA Settings vs Turbo Mode Rate .......................... 9 Effective Resolution vs Data Rate and Gain Setting ............. 10 Effective Resolution cs Data Rate and Turbo Mode Rate ..... 12 Noise Level vs Data Rate and Turbo Mode Rate .................. 12 Effective Resolution vs Data Rate, Clock Frequency, and Turbo Mode Rate .................................................................... 12 ADS1210/11 Registers ............................................................ 18 Instruction Register .................................................................. 19 A3-A0 Addressing .................................................................... 19 Organization of the Command Register and Default Status .. 19 Decimation Ratios vs Data Rates ........................................... 21 Data Output Register ............................................................... 21 Offset Calibration Register ...................................................... 22 Full-Scale Calibration Register ................................................ 22 Digital Timing Characteristics .................................................. 23 ® 41 ADS1210, 1211