ADS8343

ADS8343 ADS8 343 SBAS183A – JANUARY 2001 – REVISED OCTOBER 2002 16-Bit, 4-Channel Serial Output Sampling ANALOG-TO-DIGITAL CONVERTER FEATURES q BIPOLAR INPUT RANGE q PIN-FOR-PIN COMPATIBLE WITH THE ADS7841 AND ADS8341 q SINGLE SUPPLY: 2.7V to 5V q 4-CHANNEL SINGLE-ENDED OR 2-CHANNEL DIFFERENTIAL INPUT q UP TO 100kHz CONVERSION RATE q 86dB SINAD q SERIAL INTERFACE q SSOP-16 PACKAGE DESCRIPTION The ADS8343 is a 4-channel, 16-bit sampling Analog-toDigital (A/D) converter with a synchronous serial interface. Typical power dissipation is 8mW at a 100kHz throughput rate and a +5V supply. The reference voltage (VREF) can be varied between 500mV and VCC/2, providing a corresponding input voltage range of ±VREF. The device includes a shutdown mode which reduces power dissipation to under 15µW. The ADS8343 is ensured down to 2.7V operation. Low power, high speed, and an onboard multiplexer make the ADS8343 ideal for battery-operated systems such as personal digital assistants, portable multi-channel data loggers, and measurement equipment. The serial interface also provides low-cost isolation for remote data acquisition. The ADS8343 is available in an SSOP-16 package and is ensured over the –40°C to +85°C temperature range. APPLICATIONS q q q q q DATA ACQUISITION TEST AND MEASUREMENT INDUSTRIAL PROCESS CONTROL PERSONAL DIGITAL ASSISTANTS BATTERY-POWERED SYSTEMS SAR DCLK CS CH0 CH1 CH2 CH3 COM VREF Four Channel Multiplexer CDAC Comparator Serial Interface and Control SHDN DIN DOUT BUSY Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2001, Texas Instruments Incorporated www.ti.com PACKAGE/ORDERING INFORMATION MAXIMUM INTEGRAL LINEARITY ERROR (LSB) 8 NO MISSING CODES ERROR (LSB) 14 SPECIFIED TEMPERATURE RANGE –40°C to +85°C PRODUCT ADS8343E PACKAGE-LEAD SSOP-16 PACKAGE DESIGNATOR(1) DBQ ORDERING NUMBER ADS8343E ADS8343E/2K5 ADS8343EB ADS8343EB/2K5 TRANSPORT MEDIA, QUANTITY Rails, 100 Tape and Reel, 2500 Rails, 100 Tape and Reel, 2500 " ADS8343EB " 6 " 15 " SSOP-16 " DBQ " –40°C to +85°C " " " " " " NOTE: (1) For the most current specifications and package information, refer to our web site at www.ti.com. ABSOLUTE MAXIMUM RATINGS(1) +VCC to GND ........................................................................ –0.3V to +6V Analog Inputs to GND ............................................ –0.3V to +VCC + 0.3V Digital Inputs to GND ........................................................... –0.3V to +6V Power Dissipation .......................................................................... 250mW Maximum Junction Temperature ................................................... +150°C Operating Temperature Range ........................................ –40°C to +85°C Storage Temperature Range ......................................... –65°C to +150°C Lead Temperature (soldering, 10s) ............................................... +300°C NOTE: (1) Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. Exposure to absolute maximum conditions for extended periods may affect device reliability. PIN CONFIGURATIONS Top View SSOP +VCC CH0 CH1 1 2 3 4 5 6 7 8 ADS8343 16 15 14 13 12 11 10 9 DCLK CS DIN BUSY DOUT GND GND +VCC ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. CH2 CH3 COM SHDN VREF PIN DESCRIPTIONS PIN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 NAME +VCC CH0 CH1 CH2 CH3 COM SHDN VREF +VCC GND GND DOUT BUSY DIN CS DCLK DESCRIPTION Power Supply, 2.7V to 5V Analog Input Channel 0 Analog Input Channel 1 Analog Input Channel 2 Analog Input Channel 3 Common reference for analog inputs. This pin is typically connected to VREF. Shutdown. When LOW, the device enters a very low power shutdown mode. Voltage Reference Input. See Electrical Characteristic Table for ranges. Power Supply, 2.7V to 5V Ground Ground Serial Data Output. Data is shifted on the falling edge of DCLK. This output is high impedance when CS is HIGH. Busy Output. This output is high impedance when CS is HIGH. Serial Data Input. If CS is LOW, data is latched on rising edge of DCLK. Chip Select Input. Controls conversion timing and enables the serial input/output register. External Clock Input. This clock runs the SAR conversion process and synchronizes serial data I/O. Maximum input clock frequency equals 2.4MHz to achieve 100kHz sampling rate. 2 ADS8343 www.ti.com SBAS183A ELECTRICAL CHARACTERISTICS: +5V At TA = –40°C to +85°C, +VCC = +5V, VREF = +2.5V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. ADS8343E PARAMETER RESOLUTION ANALOG INPUT Full-Scale Input Span Absolute Input Range Capacitance Leakage Current SYSTEM PERFORMANCE No Missing Codes Integral Linearity Error Bipolar Error Bipolar Error Match Gain Error Gain Error Match Noise Power-Supply Rejection SAMPLING DYNAMICS Conversion Time Acquisition Time Throughput Rate Multiplexer Settling Time Aperture Delay Aperture Jitter Internal Clock Frequency External Clock Frequency DYNAMIC CHARACTERISTICS Total Harmonic Distortion(2) Signal-to-(Noise + Distortion) Spurious-Free Dynamic Range Channel-to-Channel Isolation REFERENCE INPUT Range Resistance Input Current 14 ±8 ±2 8.0 ±0.05 4.0 Positive Input-Negative Input Positive Input Negative Input –VREF –0.2 –0.2 25 ±1 15 ±6 ±1 ✻ ±0.024 ✻ CONDITIONS MIN TYP MAX 16 +VREF +VCC + 0.2 +VCC + 0.2 ✻ ✻ ✻ ✻ ✻ MIN ADS8343EB TYP MAX ✻ ✻ ✻ ✻ UNITS Bits V V V pF µA Bits LSB mV LSB(1) % LSB µVrms LSB(1) Clk Cycles Clk Cycles kHz ns ns ps MHz MHz MHz dB dB dB dB ✻ ✻ ✻ ✻ ✻ ✻ 5.5 +0.8 ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ 3 10 +85 ✻ ✻ ✻ ✻ ✻ ✻ V V V V ✻ ✻ V GΩ µA µA µA 2.3 1.0 20 3 ✻ ✻ ✻ ✻ +4.75V < VCC < 5.25V 16 4.5 100 500 30 100 2.4 0.024 0 –95 86 97 100 0.5 DCLK Static fSAMPLE = 12.5kHz DCLK Static 5 40 2.5 0.001 CMOS | IIH | ≤ +5µA | IIL | ≤ +5µA IOH = –250µA IOL = 250µA 3.0 –0.3 3.5 +VCC/2 100 3 ✻ 2.4 2.4 ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ SHDN = VDD Data Transfer Only VIN VIN VIN VIN = = = = 5Vp-p 5Vp-p 5Vp-p 5Vp-p at at at at 10kHz 10kHz 10kHz 50kHz ✻ ✻ DIGITAL INPUT/OUTPUT Logic Family Logic Levels VIH VIL VOH VOL Data Format POWER-SUPPLY REQUIREMENTS +VCC Quiescent Current 0.4 Binary Two’s Complement 4.75 1.5 150 7.5 –40 5.25 2.0 Specified Performance fSAMPLE = 10kHz Power-Down Mode(3, 4), CS = +VCC Power Dissipation TEMPERATURE RANGE Specified Performance ✻ Same specifications as ADS8343E. V mA µA µA mW °C NOTES: (1) LSB means Least Significant Bit. With VREF equal to +2.5V, one LSB is 76µV. (2) First nine harmonics of the test frequency. (3) Auto power-down mode (PD1 = PD0 = 0) active or SHDN = GND. (4) Power-down after conversion mode with external clock gated ‘HIGH’. ADS8343 SBAS183A www.ti.com 3 ELECTRICAL CHARACTERISTICS: +2.7V At TA = –40°C to +85°C, +VCC = +2.7V, VREF = +1.25V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. ADS8343E PARAMETER RESOLUTION ANALOG INPUT Full-Scale Input Span Absolute Input Range Capacitance Leakage Current SYSTEM PERFORMANCE No Missing Codes Integral Linearity Error Bipolar Error Bipolar Error Match Gain Error Gain Error Match Noise Power-Supply Rejection SAMPLING DYNAMICS Conversion Time Acquisition Time Throughput Rate Multiplexer Settling Time Aperture Delay Aperture Jitter Internal Clock Frequency External Clock Frequency 14 ±12 ±1 4.0 ±0.05 4.0 Positive Input-Negative Input Positive Input Negative Input –VREF –0.2 –0.2 25 ±1 15 ±8 ±0.5 ✻ ±0.0024 ✻ CONDITIONS MIN TYP MAX 16 +VREF +VCC + 0.2 +VCC + 0.2 ✻ ✻ ✻ ✻ ✻ MIN ADS8343EB TYP MAX ✻ ✻ ✻ ✻ UNITS BITS V V V pF µA Bits LSB mV LSB % of FSR LSB µVrms LSB(1) Clk Cycles Clk Cycles kHz ns ns ps MHz MHz MHz MHz 1.2 1.0 20 3 ✻ ✻ ✻ ✻ +2.7 < VCC < +3.3V 16 4.5 100 500 30 100 2.4 0.024 0.024 0 2.4 2.0 2.4 ✻ ✻ ✻ ✻ ✻ ✻ ✻ +VCC/2 5 13 2.5 0.001 CMOS | IIH | ≤ +5µA | IIL | ≤ +5µA IOH = –250µA IOL = 250µA +VCC • 0.7 –0.3 +VCC • 0.8 5.5 +0.8 ✻ ✻ ✻ 40 3 ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ SHDN = VDD When Used with Internal Clock Data Transfer Only ✻ ✻ ✻ DYNAMIC CHARACTERISTICS Total Harmonic Distortion(2) Signal-to-(Noise + Distortion) Spurious-Free Dynamic Range Channel-to-Channel Isolation REFERENCE INPUT Range Resistance Input Current VIN = 2.5Vp-p at 1kHz VIN = 2.5Vp-p at 1kHz VIN = 2.5Vp-p at 1kHz VIN = 2.5Vp-p at 10kHz 0.5 DCLK Static fSAMPLE = 12.5kHz DCLK Static DIGITAL INPUT/OUTPUT Logic Family Logic Levels VIH VIL VOH VOL Data Format POWER-SUPPLY REQUIREMENTS +VCC Quiescent Current –94 81 98 100 dB dB dB dB ✻ ✻ ✻ V GΩ µA µA µA ✻ ✻ ✻ ✻ 0.4 Binary Two’s Complement 2.7 1.2 105 3.2 –40 3.6 1.85 3 5 +85 ✻ ✻ ✻ V V V V Specified Performance fSAMPLE = 10kHz Power-Down Mode(3, 4), CS = +VCC ✻ ✻ ✻ ✻ ✻ Power Dissipation TEMPERATURE RANGE Specified Performance ✻ Same specifications as ADS8343E. V mA µA µA mW °C NOTES: (1) LSB means Least Significant Bit. With VREF equal to +1.25V, one LSB is 38µV. (2) First nine harmonics of the test frequency. (3) Auto power-down mode (PD1 = PD0 = 0) active or SHDN = GND. (4) Power-down after conversion mode with external clock gated ‘HIGH’. 4 ADS8343 www.ti.com SBAS183A TYPICAL CHARACTERISTICS: +5V At TA = +25°C, +VCC = +5V, VREF = +2.5V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. FREQUENCY SPECTRUM (4096 Point FFT; fIN = 1.001kHz, –0.2dB) 0 –20 –40 0 –20 –40 FREQUENCY SPECTRUM (4096 Point FFT; fIN = 9.985kHz, –0.2dB) Amplitude (dB) –60 –80 –100 –120 –140 0 10 20 30 40 50 Frequency (kHz) Amplitude (dB) –60 –80 –100 –120 –140 0 10 20 30 40 50 Frequency (kHz) SIGNAL-TO-NOISE RATIO AND SIGNAL-TO-(NOISE + DISTORTION) vs INPUT FREQUENCY 100 110 SPURIOUS-FREE DYNAMIC RANGE AND TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY –110 SFDR SNR and SINAD (dB) 90 SNR 100 –100 SFDR (dB) 80 SINAD 70 80 THD(1) –80 70 NOTE: (1) First nine harmonics of the input frequency. 1 10 Frequency (kHz) –70 60 1 10 Frequency (kHz) 100 60 –60 100 EFFECTIVE NUMBER OF BITS vs INPUT FREQUENCY 15.0 14.5 Effective Number of Bits Delta from 25°C (dB) 14.0 13.5 13.0 12.5 12.0 11.5 11.0 1 10 Frequency (kHz) 100 CHANGE IN SIGNAL-TO-(NOISE + DISTORTION) vs TEMPERATURE 0.1 fIN = 4.956kHz, –0.2dB 0 –0.1 –0.2 –0.3 –50 –25 0 25 Temperature (°C) 50 75 100 ADS8343 SBAS183A www.ti.com 5 THD (dB) 90 –90 TYPICAL CHARACTERISTICS: +5V (Cont.) At TA = +25°C, +VCC = +5V, VREF = +2.5V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. INTEGRAL LINEARITY ERROR vs CODE 3 2 4 3 DIFFERENTIAL LINEARITY ERROR vs CODE 0 –1 –2 –3 –4 8000H DLE (LSBs) 0000H Output Code 1 2 1 0 –1 –2 –3 8000H ILE (LSBs) C000H 4000H 7FFFH C000H 0000H Output Code 4000H 7FFFH SUPPLY CURRENT vs TEMPERATURE 1.6 1 CHANGE IN BPZ vs TEMPERATURE Supply Current (mA) 1.5 Delta from 25°C (LSBs) –50 –25 0 25 50 75 100 0 –1 1.4 –2 1.3 –3 1.2 Temperature (°C) –4 –50 –25 0 25 50 75 100 Temperature (°C) CHANGE IN GAIN vs TEMPERATURE 1.0 4.5 WORST-CASE CHANNEL-TO-CHANNEL BPZ MATCH vs TEMPERATURE Delta from 25°C (LSBs) 0.5 BPZ Match (LSBs) 4.0 0 3.5 –0.5 –50 –25 0 25 50 75 100 Temperature (°C) 3.0 –50 –25 0 25 50 75 100 Temperature (°C) 6 ADS8343 www.ti.com SBAS183A TYPICAL CHARACTERISTICS: +5V (Cont.) At TA = +25°C, +VCC = +5V, VREF = +2.5V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. WORST CASE CHANNEL-TO-CHANNEL GAIN MATCH vs TEMPERATURE 0.4 100 COMMON-MODE REJECTION vs FREQUENCY 0.3 Gain Match (LSBs) 90 CMRR (dB) 0.2 80 0.1 70 0 60 VCM = 2Vp-p Sinewave Centered Around VREF –0.1 –50 –25 0 25 50 75 100 Temperature (°C) 50 0.1 1 Frequency (kHz) 10 100 TYPICAL CHARACTERISTICS: +2.7V At TA = +25°C, +VCC = +2.7V, VREF = +1.25V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. FREQUENCY SPECTRUM (4096 Point FFT; fIN = 1.001kHz, –0.2dB) 0 –20 –40 0 –20 –40 FREQUENCY SPECTRUM (4096 Point FFT; fIN = 9.985kHz, –0.2dB) Amplitude (dB) –60 –80 –100 –120 –140 0 10 20 30 40 50 Frequency (kHz) Amplitude (dB) –60 –80 –100 –120 –140 0 10 20 30 40 50 Frequency (kHz) SIGNAL-TO-NOISE RATIO AND SIGNAL-TO-(NOISE + DISTORTION) vs INPUT FREQUENCY 95 100 SPURIOUS-FREE DYNAMIC RANGE AND TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY –100 SNR and SINAD (dB) 85 SNR 90 SFDR SFDR (dB) –90 75 SINAD 65 70 THD(1) –70 60 NOTE: (1) First nine harmonics of the input frequency. 55 1 10 Frequency (kHz) 100 500 1 10 Frequency (kHz) –60 –50 100 ADS8343 SBAS183A www.ti.com 7 THD (dB) 80 –80 TYPICAL CHARACTERISTICS: +2.7V (Cont.) At TA = +25°C, +VCC = +2.7V, VREF = +1.25V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. EFFECTIVE NUMBER OF BITS vs INPUT FREQUENCY 14.0 13.5 Effective Number of Bits Delta from 25°C (dB) 13.0 12.5 12.0 11.5 11.0 10.5 10.0 9.5 9.0 1 10 Frequency (kHz) 100 –0.8 –50 0.2 0 –0.2 –0.4 –0.6 0.4 CHANGE IN SIGNAL-TO-(NOISE + DISTORTION) vs TEMPERATURE fIN = 4.956kHz, –0.2dB –25 0 25 Temperature (°C) 50 75 100 INTEGRAL LINEARITY ERROR vs CODE 3 2 4 3 DIFFERENTIAL LINEARITY ERROR vs CODE ILE (LSBs) 1 0 –1 –2 –3 8000H DLE (LSBs) 2 1 0 –1 –2 –3 8000H C000H 0000H Output Code 4000H 7FFFH C000H 0000H Output Code 4000H 7FFFH SUPPLY CURRENT vs TEMPERATURE 1.2 1.0 CHANGE IN BPZ vs TEMPERATURE Delta from 25°C (LSBs) –50 –25 0 25 50 75 100 Supply Current (mA) 0.5 1.1 0 1.0 –0.5 0.9 Temperature (°C) –1.0 –50 –25 0 25 50 75 100 Temperature (°C) 8 ADS8343 www.ti.com SBAS183A TYPICAL CHARACTERISTICS: +2.7V (Cont.) At TA = +25°C, +VCC = +2.7V, VREF = +1.25V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. CHANGE IN GAIN vs TEMPERATURE 0.5 1.5 WORST-CASE CHANNEL-TO-CHANNEL BPZ MATCH vs TEMPERATURE Delta from 25°C (LSBs) 0 BPZ Match (LSBs) 1.0 –0.5 0.5 –1.0 –50 –25 0 25 50 75 100 Temperature (°C) 0 –50 –25 0 25 50 75 100 Temperature (°C) WORST-CASE CHANNEL-TO-CHANNEL GAIN MATCH vs TEMPERATURE 0.16 80 COMMON-MODE REJECTION vs FREQUENCY 0.15 Gain Match (LSBs) 70 CMRR (dB) 0.14 60 0.13 50 VCM = 1Vp-p Sinewave Centered Around VREF –50 –25 0 25 50 75 100 40 0.1 1 Frequency (kHz) 10 100 Temperature (°C) 0.12 POWER-DOWN SUPPLY CURRENT vs TEMPERATURE 140 External Clock Disabled 120 Supply Current (mA) SUPPLY CURRENT vs +VSS 1.4 fSAMPLE = 100kHz Supply Current (mA) 1.3 100 80 60 40 20 0 –50 –25 0 25 50 75 100 Temperature (°C) 1.2 1.1 1.0 2.5 3.0 3.5 +VSS (V) 4.0 4.5 5.0 ADS8343 SBAS183A www.ti.com 9 TYPICAL CHARACTERISTICS: +2.7V (Cont.) At TA = +25°C, +VCC = +2.7V, VREF = +1.25V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. SUPPLY CURRENT vs SAMPLING FREQUENCY 1.4 1.2 Supply Current (mA) fCLK = 2.4MHz 1.0 VSS = 5.0V 0.8 0.6 0.4 0.2 0 10 20 VSS = 2.7V Power-Down After Conversion Mode. External Clock Gated HIGH After Conversion. 30 40 50 60 70 80 90 100 Sampling Frequency (kHz) THEORY OF OPERATION The ADS8343 is a classic Successive Approximation Register (SAR) A/D converter. The architecture is based on capacitive redistribution which inherently includes a sample-and-hold function. The converter is fabricated on a 0.6µm CMOS process. The basic operation of the ADS8343 is shown in Figure 1. The device requires an external reference and an external clock. It operates from a single supply of 2.7V to 5.25V. The external reference can be any voltage between 500mV and +VCC/2. The value of the reference voltage directly sets the input range of the converter. The average reference input current depends on the conversion rate of the ADS8343. +2.7V to +5V ADS8343 + 1µF to 10µF 0.1µF 1 2 3 4 5 6 7 VREF 1µF 8 +VCC CH0 CH1 CH2 CH3 COM SHDN VREF DCLK 16 CS 15 DIN 14 BUSY 13 DOUT 12 GND 11 GND 10 +VCC 9 Serial Data Out Serial/Conversion Clock Chip Select Serial Data In The analog input to the converter is differential and is provided via a 4-channel multiplexer. The input can be provided in reference to a voltage on the COM pin (which is generally VREF) or differentially by using two of the four input channels (CH0-CH3). The particular configuration is selectable via the digital interface. ANALOG INPUT The analog input is bipolar and fully differential. There are two general methods of driving the analog input of the ADS8343: single-ended or differential, as shown in Figure 2. 2 • VREF peak-to-peak Common Voltage (typically VREF) CHX ADS8343 COM Single-ended or differential analog inputs. Single-Ended Input VREF peak-to-peak Common Voltage VREF peak-to-peak Differential Input CHX ADS8343 COM FIGURE 1. Basic Operation of the ADS8343. FIGURE 2. Methods of Driving the ADS8343—Single-Ended or Differential. 10 ADS8343 www.ti.com SBAS183A When the input is single-ended, the COM input is held at a fixed voltage. The CHX input swings around the same voltage and the peak-to-peak amplitude is 2 • VREF. The value of VREF determines the range over which the common voltage may vary, as shown in Figure 3. 5 4.9 4 VCC = 5V In each case, care should be taken to ensure that the output impedance of the sources driving the CHX and COM inputs are matched. If this is not observed, the two inputs could have different settling times. This may result in offset error, gain error, and linearity error which change with both temperature and input voltage. If the impedance cannot be matched, the errors can be lessened by giving the ADS8343 additional acquisition time. The input current on the analog inputs depends on a number of factors: sample rate, input voltage, and source impedance. Essentially, the current into the ADS8343 charges the internal capacitor array during the sample period. After this capacitance has been fully charged, there is no further input current. Care must be taken regarding the absolute analog input voltage. Outside of these ranges, the converter’s linearity may not meet specifications. Please refer to the electrical characteristics table for min/max ratings. Common Voltage Range (V) 3 Single-Ended Input 2.8 2.1 2 1 0.1 0 REFERENCE INPUT –1 0.5 1.0 1.5 VREF (V) 2.0 2.5 FIGURE 3. Single-Ended Input—Common Voltage Range vs VREF. When the input is differential, the amplitude of the input is the difference between the CHX and COM input. A voltage or signal is common to both of these inputs. The peak-to-peak amplitude of each input is VREF about this common voltage. However, since the inputs are 180° out-of-phase, the peakto-peak amplitude of the difference voltage is 2 • VREF. The value of VREF also determines the range of the voltage that may be common to both inputs, as shown in Figure 4. The external reference sets the analog input range. The ADS8343 will operate with a reference in the range of 500mV to +VCC/2. Keep in mind that the analog input is the difference between the CHX input and the COM input, as shown in Figure 5. For example, in the single-ended mode, a 1.25V reference, and with the COM pin at VREF, the selected input channel (CH0-CH3) will properly digitize a signal in the range of 0V to 1.25V. If the COM pin is connected to 0.5V, the input range on the selected channel is 0.5V to 1.75V. A2-A0 (Shown 001B) CH0 CH1 CH2 5.2 5 VCC = 5V 4.2 4 CH3 +IN Converter –IN Common Voltage Range (V) 3 Differential Input COM SGL/DIF (Shown HIGH) 2 FIGURE 5. Simplified Diagram of the Analog Input. 1 0.2 0 0.0 1.0 1.5 VREF (V) 2.0 2.5 0.8 FIGURE 4. Differential Input—Common Voltage Range vs VREF. There are several critical items concerning the reference input and its wide voltage range. As the reference voltage is reduced, the analog voltage weight of each digital output code is also reduced. This is often referred to as the LSB (Least Significant Bit) size and is equal to the reference voltage divided by 65,536. Any offset or gain error inherent in the A/D converter will appear to increase, in terms of LSB ADS8343 SBAS183A www.ti.com 11 size, as the reference voltage is reduced. For example, if the offset of a given converter is 2LSBs with a 2.5V reference, then it will typically be 10LSBs with a 0.5V reference. In each case, the actual offset of the device is the same, 76µV. The noise or uncertainty of the digitized output will increase with lower LSB size. With a reference voltage of 500mV, the LSB size is 7.6µV. This level is below the internal noise of the device. As a result, the digital output code will not be stable and vary around a mean value by a number of LSBs. The distribution of output codes will be gaussian and the noise can be reduced by simply averaging consecutive conversion results or applying a digital filter. With a lower reference voltage, care should be taken to provide a clean layout including adequate bypassing, a clean (low-noise, low-ripple) power supply, a low-noise reference, and a low-noise input signal. Because the LSB size is lower, the converter will also be more sensitive to nearby digital signals and electromagnetic interference. The voltage into the VREF input is not buffered and directly drives the Capacitor Digital-to-Analog Converter (CDAC) portion of the ADS8343. Typically, the input current is 13µA with a 2.5V reference. This value will vary by microamps depending on the result of the conversion. The reference current diminishes directly with both conversion rate and reference voltage. As the current from the reference is drawn on each bit decision, clocking the converter more quickly during a given conversion period will not reduce overall current drain from the reference. converter enters the conversion mode. At this point, the input sample-and-hold goes into the hold mode. The next 16 clock cycles accomplish the actual A/D conversion. Control Byte Also shown in Figure 6 is the placement and order of the control bits within the control byte. Tables I and II give detailed information about these bits. The first bit, the ‘S’ bit, must always be HIGH and indicates the start of the control byte. The ADS8343 will ignore inputs on the DIN pin until the start bit is detected. The next three bits (A2-A0) select the active input channel or channels of the input multiplexer, as shown in Tables III and IV and Figure 5. Bit 7 (MSB) S Bit 0 (LSB) PD0 Bit 6 A2 Bit 5 A1 Bit 4 A0 Bit 3 — Bit 2 SGL/DIF Bit 1 PD1 TABLE I. Order of the Control Bits in the Control Byte. BIT 7 6-4 2 NAME S A2-A0 SGL/DIF DESCRIPTION Start Bit. Control byte starts with first HIGH bit on DIN. Channel Select Bits. Along with the SGL/DIF bit, these bits control the setting of the multiplexer input. Single-Ended/Differential Select Bit. Along with bits A2-A0, this bit controls the setting of the multiplexer input. Power-Down Mode Select Bits. See Table V for details. 1-0 PD1-PD0 DIGITAL INTERFACE Figure 6 shows the typical operation of the ADS8343’s digital interface. This diagram assumes that the source of the digital signals is a microcontroller or digital signal processor with a basic serial interface (note that the digital inputs are overvoltage tolerant up to 5.5V, regardless of +VCC). Each communication between the processor and the converter consists of eight clock cycles. One complete conversion can be accomplished with three serial communications, for a total of 24 clock cycles on the DCLK input. The first eight cycles are used to provide the control byte via the DIN pin. When the converter has enough information about the following conversion to set the input multiplexer appropriately, it enters the acquisition (sample) mode. After three more clock cycles, the control byte is complete and the TABLE II. Descriptions of the Control Bits within the Control Byte. A2 0 1 0 1 A1 0 0 1 1 A0 1 1 0 0 CH0 +IN +IN +IN +IN CH1 CH2 CH3 COM –IN –IN –IN –IN TABLE III. Single-Ended Channel Selection (SGL/DIF HIGH). A2 0 1 0 1 A1 0 0 1 1 A0 1 1 0 0 CH0 +IN –IN CH1 –IN +IN +IN –IN –IN +IN CH2 CH3 COM TABLE IV. Differential Channel Control (SGL/DIF LOW). CS tACQ DCLK 1 Idle Acquire A1 A0 8 1 8 Conversion 1 8 1 Idle S A2 A1 A0 Acquire 8 1 Conversion DIN S A2 SGL/ PD1 PD0 DIF SGL/ PD1 PD0 DIF (START) (START) BUSY DOUT 15 (MSB) 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 (LSB) Zero Filled... 15 (MSB) 14 FIGURE 6. Conversion Timing, 24-Clocks per Conversion, 8-Bit Bus Interface. No DCLK delay required with dedicated serial port. 12 ADS8343 www.ti.com SBAS183A The SGL/DIF bit controls the multiplexer input mode: either single-ended (HIGH) or differential (LOW). In single-ended mode, the selected input channel is referenced to the COM pin. In differential mode, the two selected inputs provide a differential input. See Tables III and IV and Figure 5 for more information. The last two bits (PD1-PD0) select the powerdown mode as shown in Table V. If both inputs are HIGH, the device is always powered up. If both inputs are LOW, the device enters a power-down mode between conversions. When a new conversion is initiated, the device will resume normal operation instantly—no delay is needed to allow the device to power up and the very first conversion will be valid. PD1 0 PD0 0 DESCRIPTION Power-down between conversions. When each conversion is finished, the converter enters a lowpower mode. At the start of the next conversion, the device instantly powers up to full power. There is no need for additional delays to assure full operation and the very first conversion is valid. Internal clock mode. Reserved for future use. No power-down between conversions, device always powered. If the user decides to switch from one clock mode to the other, an extra conversion cycle will be required before the ADS8343 can switch to the new mode. The extra cycle is required because the PD0 and PD1 control bits need to be written to the ADS8343 prior to the change in clock modes. NOTE: It is recommended that the customer write to the PD1 and PD0 registers prior to the first conversion in order to insure that the proper clock mode is selected. External Clock Mode In external clock mode, the external clock not only shifts data in and out of the ADS8343, it also controls the A/D conversion steps. BUSY will go HIGH for one clock period after the last bit of the control byte is shifted in. Successive-approximation bit decisions are made and appear at DOUT on each of the next 16 SCLK falling edges, see Figure 6. Figure 7 shows the BUSY timing in external clock mode. Since one clock cycle of the serial clock is consumed with BUSY going HIGH (while the MSB decision is being made), 16 additional clocks must be given to clock out all 16 bits of data; thus, one conversion takes a minimum of 25 clock cycles to fully read the data. Since most microprocessors communicate in 8-bit transfers, this means that an additional transfer must be made to capture the LSB. There are two ways of handling this requirement. One is presented in Figure 6, where the beginning of the next control byte appears at the same time the LSB is being clocked out of the ADS8343. This method allows for maximum throughput and 24 clock cycles per conversion. 1 0 1 0 1 1 TABLE V. Power-Down Selection. Clock Modes The ADS8343 can be used with an external serial clock or an internal clock to perform the successive-approximation conversion. In both clock modes, the external clock shifts data in and out of the device. Internal clock mode is selected when PD1 is HIGH and PD0 is LOW. CS tCSS DCLK tDS DIN tBDV BUSY tDV DOUT 15 14 tTR tDH PD0 tBTR tCH tCL tBD tBD tD0 tCSH FIGURE 7. Detailed Timing Diagram. ADS8343 SBAS183A www.ti.com 13 The other method is shown in Figure 8, which uses 32 clock cycles per conversion; the last seven clock cycles simply shift out zeros on the DOUT line. BUSY and DOUT go into a high-impedance state when CS goes HIGH; after the next CS falling edge, BUSY will go LOW. SYMBOL tACQ tDS tDH tDO tDV tTR tCSS tCSH tCH tCL tBD tBDV tBTR DESCRIPTION Acquisition Time DIN Valid Prior to DCLK Rising DIN Hold After DCLK HIGH DCLK Falling to DOUT Valid CS Falling to DOUT Enabled CS Rising to DOUT Disabled CS Falling to First DCLK Rising CS Rising to DCLK Ignored DCLK HIGH DCLK LOW DCLK Falling to BUSY Rising CS Falling to BUSY Enabled CS Rising to BUSY Disabled MIN 1.5 100 10 TYP MAX UNITS µs ns ns 200 200 200 100 0 200 200 200 200 200 ns ns ns ns ns ns ns ns ns ns Internal Clock Mode In internal clock mode, the ADS8343 generates its own conversion clock internally. This relieves the microprocessor from having to generate the SAR conversion clock and allows the conversion result to be read back at the processor’s convenience, at any clock rate from 0MHz to 2.0MHz. BUSY goes LOW at the start of conversion and then returns HIGH when the conversion is complete. During the conversion, BUSY will remain LOW for a maximum of 8µs. Also, during the conversion, SCLK should remain LOW to achieve the best noise performance. The conversion result is stored in an internal register; the data may be clocked out of this register any time after the conversion is complete. If CS is LOW when BUSY goes LOW following a conversion, the next falling edge of the external serial clock will write out the MSB on the DOUT line. The remaining bits (D14-D0) will be clocked out on each successive clock cycle following the MSB. If CS is HIGH when BUSY goes LOW then the DOUT line will remain in tri-state until CS goes LOW, as shown in Figure 9. CS does not need to remain LOW once a conversion has started. Note that BUSY is not tri-stated when CS goes HIGH in internal clock mode. Data can be shifted in and out of the ADS8343 at clock rates exceeding 2.4MHz, provided that the minimum acquisition time tACQ, is kept above 1.7µs. TABLE VI. Timing Specifications (+VCC = +2.7V to 3.6V, TA = –40°C to +85°C, CLOAD = 50pF). SYMBOL tACQ tDS tDH tDO tDV tTR tCSS tCSH tCH tCL tBD tBDV tBTR DESCRIPTION Acquisition Time DIN Valid Prior to DCLK Rising DIN Hold After DCLK HIGH DCLK Falling to DOUT Valid CS Falling to DOUT Enabled CS Rising to DOUT Disabled CS Falling to First DCLK Rising CS Rising to DCLK Ignored DCLK HIGH DCLK LOW DCLK Falling to BUSY Rising CS Falling to BUSY Enabled CS Rising to BUSY Disabled 50 0 150 150 100 70 70 MIN 1.7 50 10 100 70 70 TYP MAX UNITS µs ns ns ns ns ns ns ns ns ns ns ns ns Digital Timing Figure 4 and Tables VI and VII provide detailed timing for the digital interface of the ADS8343. CS tACQ TABLE VII. Timing Specifications (+VCC = +4.75V to +5.25V, TA = –40°C to +85°C, CLOAD = 50pF). DCLK 1 Idle Acquire A1 A0 8 1 8 Conversion 1 8 1 Idle 8 DIN S A2 SGL/ DIF PD1 PD0 (START) BUSY DOUT 15 (MSB) 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 (LSB) Zero Filled... FIGURE 8. External Clock Mode 32 Clocks Per Conversion. CS tACQ DCLK 1 Idle Acquire A1 A0 8 Conversion 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 DIN S A2 SGL/ DIF PD1 PD0 (START) BUSY DOUT 15 (MSB) 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 (LSB) Zero Filled... FIGURE 9. Internal Clock Mode Timing. 14 ADS8343 www.ti.com SBAS183A DATA FORMAT The output data from the ADS8343 is in Binary Two’s Complement format, as shown in Table VIII. This table represents the ideal output code for the given input voltage and does not include the effects of offset, gain, or noise. DESCRIPTION Full-Scale Range Least Significant Bit (LSB) +Full-Scale Midscale Midscale – 1LSB –Full-Scale ANALOG VALUE 2 • VREF 2 • VREF/65536 BINARY CODE +VREF – 1LSB 0V 0V – 1LSB –VREF 0111 1111 1111 1111 0000 0000 0000 0000 1111 1111 1111 1111 1000 0000 0000 0000 HEX CODE 7FFF 0000 FFFF 8000 If DCLK is active and CS is LOW while the ADS8343 is in auto power-down mode, the device will continue to dissipate some power in the digital logic. The power can be reduced to a minimum by keeping CS HIGH. The differences in supply current for these two cases are shown in Figure 11. Operating the ADS8343 in auto power-down mode will result in the lowest power dissipation, and there is no conversion time “penalty” on power-up. The very first conversion will be valid. SHDN can be used to force an immediate power-down. DIGITAL OUTPUT BINARY TWO’S COMPLEMENT 1000 fCLK = 24 • fSAMPLE Supply Current (µA) TABLE VIII. Ideal Input Voltages and Output Codes. 100 POWER DISSIPATION There are three power modes for the ADS8343: full-power (PD1 = PD0 = 1B), auto power-down (PD1 = PD0 = 0B), and shutdown (SHDN LOW). The affects of these modes varies depending on how the ADS8343 is being operated. For example, at full conversion rate and 24-clocks per conversion, there is very little difference between full-power mode and auto power-down, a shutdown (SHDN LOW) will not lower power dissipation. When operating at full-speed and 24 clocks per conversion (see Figure 6), the ADS8343 spends most of its time acquiring or converting. There is little time for auto power-down, assuming that this mode is active. Thus, the difference between full-power mode and auto power-down is negligible. If the conversion rate is decreased by simply slowing the frequency of the DCLK input, the two modes remain approximately equal. However, if the DCLK frequency is kept at the maximum rate during a conversion, but conversion are simply done less often, then the difference between the two modes is dramatic. Figure 10 shows the difference between reducing the DCLK frequency (“scaling” DCLK to match the conversion rate) or maintaining DCLK at the highest frequency and reducing the number of conversion per second. In the later case, the converter spends an increasing percentage of its time in power-down mode (assuming the auto power-down mode is active). 10 fCLK = 2.4MHz TA = 25°C +VCC = +2.7V VREF = +2.5V PD1 = PD0 = 0 1k 10k fSAMPLE (Hz) 100k 1M 1 FIGURE 10. Supply Current versus Directly Scaling the Frequency of DCLK with Sample Rate or Keeping DCLK at the Maximum Possible Frequency. 14 12 Supply Current (µA) 10 8 6 4 2 TA = 25°C +VCC = +2.7V VREF = +2.5V fCLK = 24 • fSAMPLE PD1 = PD0 = 0 CS LOW (GND) CS HIGH (+VCC) 0 0.09 0.00 1k 10k fSAMPLE (Hz) 100k 1M FIGURE 11. Supply Current vs State of CS . ADS8343 SBAS183A www.ti.com 15 NOISE The noise floor of the ADS8343 itself is extremely low, as can be seen from Figures 12 and 13, and is much lower than competing A/D converters. The ADS8343 was tested at both 5V and 2.7V and in both the internal and external clock modes. A low-level DC input was applied to the analog input pins and the converter was put through 5000 conversions. The digital output of the A/D converter will vary in output code due to the internal noise of the ADS8343. This is true for all 16-bit, SAR-type, A/D converters. Using a histogram to plot the output codes, the distribution should appear bell-shaped with the peak of the bell curve representing the nominal code for the input value. The ±1σ, ±2σ, and ±3σ distributions will represent the 68.3%, 95.5%, and 99.7%, respectively, of all codes. The transition noise can be calculated by dividing the number of codes measured by 6 and this will yield the ±3σ distribution or 99.7% of all codes. Statistically, up to 3 codes could fall outside the distribution when executing 1000 conversions. The ADS8343, with < 3 output codes for the ±3σ distribution, will yield a < ±0.5LSB transition noise at 5V operation. Remember, to achieve this low noise performance, the peak-to-peak noise of the input signal and reference must be < 50µV. 3295 AVERAGING The noise of the A/D converter can be compensated by averaging the digital codes. By averaging conversion results, transition noise will be reduced by a factor of 1/√n , where n is the number of averages. For example, averaging 4 conversion results will reduce the transition noise by 1/2 to ±0.25LSBs. Averaging should only be used for input signals with frequencies near DC. For AC signals, a digital filter can be used to low-pass filter and decimate the output codes. This works in a similar manner to averaging; for every decimation by 2, the signalto-noise ratio will improve 3dB. LAYOUT For optimum performance, care should be taken with the physical layout of the ADS8343 circuitry. This is particularly true if the reference voltage is low and/or the conversion rate is high. The basic SAR architecture is sensitive to glitches or sudden changes on the power supply, reference, ground connections, and digital inputs that occur just prior to latching the output of the analog comparator. Thus, during any single conversion for an nbit SAR converter, there are n “windows” in which large external transient voltages can easily affect the conversion result. Such glitches might originate from switching power supplies, nearby digital logic, and high-power devices. The degree of error in the digital output depends on the reference voltage, layout, and the exact timing of the external event. The error can change if the external event changes in time with respect to the DCLK input. With this in mind, power to the ADS8343 should be clean and well bypassed. A 0.1µF ceramic bypass capacitor should be placed as close to the device as possible. In addition, a 1µF to 10µF capacitor and a 5Ω or 10Ω series resistor may be used to low-pass filter a noisy supply. 774 705 131 95 FFFEH FFFFH 0000H Code 0001H 0002H FIGURE 12. Histogram of 5000 Conversions of a DC Input at the Code Transition, 5V Operation External Clock Mode. 2387 The reference should be similarly bypassed with a 1µF capacitor. Again, a series resistor and large capacitor can be used to low-pass filter the reference voltage. If the reference voltage originates from an op amp, make sure that it can drive the bypass capacitor without oscillation (the series resistor can help in this case). The ADS8343 draws very little current from the reference on average, but it does place larger demands on the reference circuitry over short periods of time (on each rising edge of DCLK during a conversion). The ADS8343 architecture offers no inherent rejection of noise or voltage variation in regards to the reference input. This is of particular concern when the reference input is tied to the power supply. Any noise and ripple from the supply will appear directly in the digital results. While high-frequency noise can be filtered out as discussed in the previous paragraph, voltage variation due to line frequency (50Hz or 60Hz) can be difficult to remove. 905 694 411 8 38 512 38 7 FFFCH FFFDH FFFEH FFFFH 0000H 0001H 0002H 0003H 0004H Code FIGURE 13. Histogram of 5000 Conversions of a DC Input at the Code Center, 2.7V Operation Internal Clock Mode. The GND pin should be connected to a clean ground point. In many cases, this will be the “analog” ground. Avoid connections which are too near the grounding point of a microcontroller or digital signal processor. If needed, run a ground trace directly from the converter to the power-supply entry point. The ideal layout will include an analog ground plane dedicated to the converter and associated analog circuitry. 16 ADS8343 www.ti.com SBAS183A PACKAGE DRAWING DBQ (R-PDSO-G**) 24 PINS SHOWN 0.012 (0,30) 0.008 (0,20) 13 PLASTIC SMALL-OUTLINE 0.025 (0,64) 24 0.005 (0,13) M 0.244 (6,20) 0.228 (5,80) 0.157 (3,99) 0.150 (3,81) 0.008 (0,20) NOM 1 A 12 Gage Plane 0.010 (0,25) 0°– 8° 0.069 (1,75) MAX 0.035 (0,89) 0.016 (0,40) Seating Plane 0.010 (0,25) 0.004 (0,10) PINS ** DIM A MAX 0.004 (0,10) 16 0.197 (5,00) 0.188 (4,78) 20 0.344 (8,74) 0.337 (8,56) 24 0.344 (8,74) 0.337 (8,56) 28 0.394 (10,01) 0.386 (9,80) 4073301/E 10/00 A MIN NOTES: A. B. C. D. All linear dimensions are in inches (millimeters). This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion not to exceed 0.006 (0,15). Falls within JEDEC MO-137 ADS8343 SBAS183A www.ti.com 17 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s standard warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily performed. 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