ADS8345 ADS 834 5 ADS 834 5 ® ® SBAS177C – FEBRUARY 2001 – REVISED APRIL 2003 16-Bit, 8-Channel Serial Output Sampling ANALOG-TO-DIGITAL CONVERTER FEATURES DESCRIPTION ● BIPOLAR INPUT RANGE The ADS8345 is an 8-channel, 16-bit, sampling Analog-to-Digital (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 ADS8345 is ensured down to 2.7V operation. ● PIN-FOR-PIN COMPATIBLE WITH THE ADS7844 AND ADS8344 ● SINGLE SUPPLY: 2.7V to 5V ● 8-CHANNEL SINGLE-ENDED OR 4-CHANNEL DIFFERENTIAL INPUT ● UP TO 100kHz CONVERSION RATE ● 85dB SINAD ● SERIAL INTERFACE ● QSOP-20 AND SSOP-20 PACKAGES Low-power, high-speed, and an onboard multiplexer make the ADS8345 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 ADS8345 is available in a QSOP-20 or SSOP-20 package and is ensured over the –40°C to +85°C temperature range. APPLICATIONS ● ● ● ● ● DATA ACQUISITION TEST AND MEASUREMENT EQUIPMENT INDUSTRIAL PROCESS CONTROL PERSONAL DIGITAL ASSISTANTS BATTERY-POWERED SYSTEMS CH0 SAR CH1 DCLK CH2 CH3 CH4 8-Channel Multiplexer CH5 CS Comparator CDAC CH6 CH7 COM Serial Interface and Control SHDN DIN DOUT BUSY VREF 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. Copyright © 2001-2003, Texas Instruments Incorporated 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. www.ti.com ABSOLUTE MAXIMUM RATINGS(1) ELECTROSTATIC DISCHARGE SENSITIVITY +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. 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. PACKAGE/ORDERING INFORMATION PRODUCT MAXIMUM INTEGRAL LINEARITY ERROR (LSB) MAXIMUM GAIN ERROR (%) ADS8345E 8 " 8 " ADS8345N " ADS8345EB " ADS8345NB " PACKAGE-LEAD PACKAGE DESIGNATOR(1) SPECIFIED TEMPERATURE RANGE ±0.05 QSOP-20 DBQ –40°C to +85°C ADS8345E Rails, 100 " " " " ADS8345E/2K5 Tape and Reel, 2500 ±0.05 SSOP-20 DB –40°C to +85°C ADS8345N Rails, 100 Tape and Reel, 1000 ORDERING NUMBER TRANSPORT MEDIA, QUANTITY " " " " " ADS8345N/1K 6 ±0.024 QSOP-20 DBQ –40°C to +85°C ADS8345EB Rails, 100 " " " " " ADS8345EB/2K5 Tape and Reel, 2500 6 ±0.024 SSOP-20 DB –40°C to +85°C ADS8345NB Rails, 100 " " " " " ADS8345NB/1K Tape and Reel, 1000 NOTE: (1) For the most current specifications and package information, refer to our web site at www.ti.com. PIN DESCRIPTIONS PIN CONFIGURATION Top View SSOP CH0 1 20 +VCC CH1 2 19 DCLK CH2 3 18 CS CH3 4 17 DIN CH4 5 16 BUSY PIN NAME 1 2 3 4 5 6 7 8 9 CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 COM 10 SHDN 11 VREF +VCC GND GND DOUT ADS8345 2 CH5 6 15 DOUT CH6 7 14 GND CH7 8 13 GND 12 13 14 15 COM 9 12 +VCC 16 BUSY SHDN 10 11 VREF 17 DIN 18 CS 19 DCLK 20 +VCC www.ti.com DESCRIPTION Analog Input Channel 0 Analog Input Channel 1 Analog Input Channel 2 Analog Input Channel 3 Analog Input Channel 4 Analog Input Channel 5 Analog Input Channel 6 Analog Input Channel 7 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 the Electrical Characteristics Table for ranges. Power Supply, 2.7V to 5.25V 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. Busy goes LOW when the DIN control bits are being read and also when the device is converting. The 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; Active LOW. Data will not be clocked into DIN unless CS is LOW. When CS is HIGH, DOUT is high impedance. External Clock Input. The clock speed determines the conversion rate by the equation fDCLK = 24 • fSAMPLE. Power Supply ADS8345 SBAS177C 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. ADS8345E, N PARAMETER CONDITIONS MIN RESOLUTION ANALOG INPUT Full-Scale Input Span Absolute Input Range Positive Input-Negative Input +IN –IN 1.0 20 3 POWER-SUPPLY REQUIREMENTS +VCC Quiescent Current ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ 100 VIN VIN VIN VIN = = = = 5Vp-p 5Vp-p 5Vp-p 5Vp-p at at at at ✻ ✻ ✻ ✻ 500 30 100 2.4 0.024 0 10kHz 10kHz 10kHz 10kHz 2.4 2.4 ✻ ✻ 0.5 +VCC/2 5 40 0.001 ✻ 100 3 3.0 –0.3 3.5 5.5 +0.8 4.75 1.5 1.2 Power Dissipation 7.5 –40 Bits LSB mV LSB(1) % LSB µVrms LSB(1) CLK Cycles CLK Cycles kHz ns ns ps MHz MHz MHz ✻ ✻ V GΩ µA µA ✻ ✻ ✻ ✻ 5.25 2.0 V V V V ✻ ✻ ✻ ✻ 3 10 +85 ✻ ✻ ✻ 0.4 Binary Two’s Complement Specified Performance V V V pF µA dB dB dB dB ✻ ✻ ✻ ✻ CMOS | IIH | ≤ +5µA | IIL | ≤ +5µA IOH = –250µA IOL = 250µA ✻ ✻ ✻ ✻ ✻ ✻ –96 85 98 105 DCLK Static ±6 ±1 ✻ ±0.024 ✻ ✻ 16 fSAMPLE = 10kHz Power-Down Mode(3), CS = +VCC TEMPERATURE RANGE Specified Performance ±8 ±2 8 ±0.05 4 4.5 DCLK Static DIGITAL INPUT/OUTPUT Logic Family Logic Levels VIH VIL VOH VOL Data Format ✻ ✻ ✻ UNITS Bits 15 4 SHDN = VDD MAX ✻ ✻ 14 +4.75V < VCC < 5.25V TYP ✻ +VREF +VCC + 0.2 +VCC + 0.2 –VREF –0.2 –0.2 Data Transfer Only REFERENCE INPUT Range Resistance Input Current MIN 25 ±1 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 MAX 16 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 TYP ADS8345EB, NB ✻ ✻ ✻ ✻ ✻ ✻ V mA mA µA mW ✻ °C ✻ Same specifications as ADS8345E, N. 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. ADS8345 SBAS177C 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. ADS8345E, N PARAMETER CONDITIONS MIN RESOLUTION ANALOG INPUT Full-Scale Input Span Absolute Input Range SAMPLING DYNAMICS Conversion Time Acquisition Time Throughput Rate Multiplexer Settling Time Aperture Delay Aperture Jitter Internal Clock Frequency External Clock Frequency Positive Input-Negative Input +IN –IN REFERENCE INPUT Range Resistance Input Current 1 20 3 POWER-SUPPLY REQUIREMENTS +VCC Quiescent Current ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ ✻ 100 ✻ ✻ ✻ ✻ 500 30 100 2.4 0.024 0.024 0 VIN = 2.5Vp-p at 1kHz VIN = 2.5Vp-p at 1kHz VIN = 2.5Vp-p at 1kHz VIN = 2.5Vp-p at 10kHz 2.4 2.0 2.4 ✻ ✻ ✻ 0.5 +VCC/2 5 13 0.001 ✻ 40 3 +VCC • 0.7 –0.3 +VCC • 0.8 5.5 +0.8 2.7 1.2 950 Power Dissipation 3.2 –40 Bits LSB mV LSB % of FSR LSB µVrms LSB(1) CLK Cycles CLK Cycles kHz ns ns ps MHz MHz MHz MHz ✻ ✻ V GΩ µA µA ✻ ✻ ✻ ✻ 3.6 1.85 V V V V ✻ ✻ ✻ ✻ 3 5 +85 ✻ ✻ ✻ 0.4 Binary Two’s Complement Specified Performance V V V pF µA dB dB dB dB ✻ ✻ ✻ ✻ CMOS | IIH | ≤ +5µA | IIL | ≤ +5µA IOH = –250µA IOL = 250µA ✻ ✻ ✻ ✻ ✻ ✻ ✻ –95 81 95 108 DCLK Static ±6 ±0.5 ✻ ±0.024 ✻ ✻ 16 4.5 fSAMPLE = 10kHz Power-Down Mode(3), CS = +VCC TEMPERATURE RANGE Specified Performance ±8 ±1.0 4 ±0.05 4 UNITS Bits 15 2 SHDN = VDD MAX ✻ ✻ 14 +2.7 < VCC < +3.3V TYP ✻ ✻ ✻ 25 ±1 DCLK Static DIGITAL INPUT/OUTPUT Logic Family Logic Levels VIH VIL VOH VOL Data Format MIN ✻ +VREF +VCC + 0.2 +VCC + 0.2 –VREF –0.2 –0.2 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 MAX 16 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 TYP ADS8345EB, NB ✻ ✻ ✻ ✻ ✻ ✻ V mA µA µA mW ✻ °C ✻ Same specifications as ADS8345E, N. 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 www.ti.com ADS8345 SBAS177C TYPICAL CHARACTERISTICS: +5V At TA = +25°C, +VCC = +5V, VREF = +2.5V, fSAMPLE = 100kHz, and fDCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. FREQUENCY SPECTRUM (4096 Point FFT; fIN = 9.985kHz, –0.2dB) 0 0 –20 –20 –40 –40 Amplitude (dB) –60 –80 –100 –60 –80 –100 –120 –120 –140 –140 0 10 20 30 40 0 50 20 30 40 Frequency (kHz) SIGNAL-TO-NOISE RATIO AND SIGNAL-TO-(NOISE + DISTORTION) vs INPUT FREQUENCY SPURIOUS-FREE DYNAMIC RANGE AND TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY 50 –110 110 100 90 SFDR 100 SNR SFDR (dB) SNR and SINAD (dB) 10 Frequency (kHz) 80 SINAD 70 –100 –90 90 (1) THD –80 80 –70 70 NOTE: (1) First Nine Harmonics of the Input Frequency 1 10 1 100 10 100 Frequency (kHz) Frequency (kHz) EFFECTIVE NUMBER OF BITS vs INPUT FREQUENCY CHANGE IN SIGNAL-TO-(NOISE + DISTORTION) vs TEMPERATURE 15.0 0.4 fIN = 4.956kHz, –0.2dB 14.5 0.2 14.0 Delta from +25°C (dB) Effective Number of Bits –60 60 60 13.5 13.0 12.5 12.0 0.0 –0.2 –0.4 –0.6 11.5 11.0 –0.8 1 10 100 ADS8345 SBAS177C –50 –25 0 20 50 75 100 Temperature (°C) Frequency (kHz) www.ti.com 5 THD (dB) Amplitude (dB) FREQUENCY SPECTRUM (4096 Point FFT; fIN = 1.001kHz, –0.2dB) TYPICAL CHARACTERISTICS: +5V (Cont.) At TA = +25°C, +VCC = +5V, VREF = +2.5V, fSAMPLE = 100kHz, and fDCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. DIFFERENTIAL LINEARITY ERROR vs CODE 3 2 2 1 1 DLE (LSB) ILE (LSB) INTEGRAL LINEARITY ERROR vs CODE 3 0 0 –1 –1 –2 –2 –3 8000H 0000H C000H 4000H –3 8000H 7FFFH C000H 7FFFH Output Code SUPPLY CURRENT vs TEMPERATURE CHANGE IN BPZ vs TEMPERATURE 1.7 4 3 Delta from 25°C (LSBs) 1.6 Supply Current (mA) 4000H 0000H Output Code 1.5 1.4 1.3 2 1 0 –1 1.2 –2 –50 –25 0 25 50 75 100 –50 –25 0 25 50 75 100 Temperature (°C) Temperature (°C) CHANGE IN GAIN vs TEMPERATURE WORST-CASE CHANNEL-TO-CHANNEL BPZ MATCH vs TEMPERATURE 1.0 5.0 BPZ Match (LSBs) Delta from 25°C (LSBs) 4.5 0.5 0 4.0 3.5 3.0 2.5 –0.5 2.0 –50 –25 0 25 50 75 100 –50 Temperature (°C) 6 –25 0 25 50 75 100 Temperature (°C) www.ti.com ADS8345 SBAS177C TYPICAL CHARACTERISTICS: +5V (Cont.) At TA = +25°C, +VCC = +2.5V, VREF = +2.5V, fSAMPLE = 100kHz, and fDCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. WORST-CASE CHANNEL-TO-CHANNEL GAIN MATCH vs TEMPERATURE COMMON-MODE REJECTION vs FREQUENCY 0.5 100 90 CMRR (dB) Gain Match (LSBs) 0.4 0.3 80 70 0.2 60 VCM = 2Vp-p Sinewave Centered Around VREF 0.1 50 –50 –25 0 25 50 75 100 0.1 1 Temperature (°C) 10 100 Frequency (kHz) TYPICAL CHARACTERISTICS: +2.7V At TA = +25°C, +VCC = +2.7V, VREF = +1.25V, fSAMPLE = 100kHz, and fDCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. FREQUENCY SPECTRUM (4096 Point FFT; fIN = 9.985kHz, –0.2dB) 0 0 –20 –20 –40 –40 Amplitude (dB) –60 –80 –60 –80 –100 –100 –120 –120 –140 –140 0 10 20 30 40 0 50 20 30 40 Frequency (kHz) Frequency (kHz) SIGNAL-TO-NOISE RATIO AND SIGNAL-TO-(NOISE + DISTORTION) vs INPUT FREQUENCY SPURIOUS-FREE DYNAMIC RANGE AND TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY SNR 50 –100 100 95 –90 90 85 SFDR SFDR (dB) SNR and SINAD (dB) 10 75 –80 80 –70 70 THD (dB) Amplitude (dB) FREQUENCY SPECTRUM (4096 Point FFT; fIN = 1.001kHz, –0.2dB) THD(1) SINAD 65 –60 60 NOTE: (1) First Nine Harmonics of the Input Frequency –50 50 55 1 10 100 Frequency (kHz) ADS8345 SBAS177C 1 10 100 Frequency (kHz) www.ti.com 7 TYPICAL CHARACTERISTICS: +2.7V (Cont.) At TA = +25°C, +VCC = +2.7V, VREF = +1.25V, fSAMPLE = 100kHz, and fDCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. EFFECTIVE NUMBER OF BITS vs INPUT FREQUENCY CHANGE IN SIGNAL-TO-(NOISE + DISTORTION) vs TEMPERATURE 0.4 14.0 fIN = 4.956kHz, –0.2dB 0.2 13.0 Delta from +25°C (dB) Effective Number of Bits 13.5 12.5 12.0 11.5 11.0 10.5 10.0 0 –0.2 –0.4 –0.6 –0.8 9.5 –1.0 9.0 1 10 –50 100 –25 0 2 2 1 1 0 –1 –2 –2 4000H 0000H –3 8000H 7FFFH C000H 100 7FFFH Output Code SUPPLY CURRENT vs TEMPERATURE CHANGE IN BPZ vs TEMPERATURE 1.0 Delta from 25°C (LSBs) 1.3 Supply Current (mA) 4000H 0000H Output Code 1.2 1.1 1.0 0.9 0.5 0 –0.5 –1.0 –50 –25 0 25 50 75 100 –50 Temperature (°C) 8 75 0 –1 C000H 50 DIFFERENTIAL LINEARITY ERROR vs CODE 3 DLE (LSB) ILE (LSB) INTEGRAL LINEARITY ERROR vs CODE 3 –3 8000H 20 Temperature (°C) Frequency (kHz) –25 0 25 50 75 100 Temperature (°C) www.ti.com ADS8345 SBAS177C TYPICAL CHARACTERISTICS: +2.7V (Cont.) At TA = +25°C, +VCC = +2.7V, VREF = +1.25V, fSAMPLE = 100kHz, and fDCLK = 24 • fSAMPLE = 2.4MHz, unless otherwise noted. WORST-CASE CHANNEL-TO-CHANNEL BPZ MATCH vs TEMPERATURE CHANGE IN GAIN vs TEMPERATURE 1.0 0.9 BPZ Match (LSBs) Delta from 25°C (LSBs) 1.0 0.5 0 0.8 0.7 0.6 0.5 –0.5 –50 –25 0 25 50 75 –50 100 –25 0 Temperature (°C) WORST-CASE CHANNEL-TO-CHANNEL GAIN MATCH vs TEMPERATURE 50 75 100 COMMON-MODE REJECTION vs FREQUENCY 0.35 80 70 0.30 CMRR (dB) Gain Match (LSBs) 25 Temperature (°C) 0.25 60 50 VCM = 1Vp-p Sinewave Centered Around VREF 0.20 40 –50 –25 0 25 50 75 100 0.1 1 Temperature (°C) POWER-DOWN SUPPLY CURRENT vs TEMPERATURE 100 SUPPLY CURRENT vs VSS 140 1.5 120 1.4 External Clock Disabled 100 Supply Current (mA) Supply Current (nA) 10 Frequency (kHz) 80 60 40 fSAMPLE = 100kHz 1.3 1.2 1.1 1.0 20 0.9 0 –50 –25 0 25 50 75 2.5 100 ADS8345 SBAS177C 3.0 3.5 4.0 4.5 5.0 +VSS (V) Temperature (°C) www.ti.com 9 THEORY OF OPERATION determines the range over which the common voltage may vary (see Figure 3). The ADS8345 is a classic Successive Approximation Register (SAR) A/D converter. The architecture is based on capacitive redistribution which inherently includes a sampleand-hold function. The converter is fabricated on a 0.6µm CMOS process. When the input is differential, the amplitude of the input is the difference between the CHX and COM input (see Figure 4). 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 input are 180°C out-ofphase, the peak-to-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 (see Figure 5). The basic operation of the ADS8345 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 ADS8345. 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 changes with both temperature and input voltage. If the impedance cannot be matched, the errors can be lessened by giving the ADS8345 additional acquisition time. The analog input to the converter is differential and is provided via an eight-channel multiplexer. The input can be provided in reference to a voltage on the COM pin (which is generally +VCC/2) or differentially by using four of the eight input channels (CH-CH7). The particular configuration is selectable via the digital interface. 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 ADS8345 charges the internal capacitor array during the sample period. After this capacitance has been fully charged, there is no further input current. ANALOG INPUT The analog input is bipolar and fully differential. There are two general methods of driving the analog input of the ADS8345: single-ended or differential (see Figure 2). 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 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. +2.7V to +5V ADS8345 Single-ended or differential analog inputs. VREF 0.1µF 1µF to 10µF 1 CH0 +VCC 20 2 CH1 DCLK 19 3 CH2 CS 18 Chip Select 4 CH3 DIN 17 Serial Data In 5 CH4 BUSY 16 6 CH5 DOUT 15 7 CH6 GND 14 8 CH7 GND 13 9 COM +VCC 12 10 SHDN VREF 11 Serial/Conversion Clock Serial Data Out +1.25V to +2.5V 1µF to 10µF FIGURE 1. Basic Operation of the ADS8345. 10 www.ti.com ADS8345 SBAS177C REFERENCE INPUT The external reference sets the analog input range. The ADS8345 will operate with a reference in the range of 500mV to +VCC/2. Keep in mind that the analog input is the differ- ence between the CHX input and the COM input, as shown in Figure 4. For example, in the single-ended mode, a 1.25V reference with the COM pin at VCC/2, the selected input channel (CH0-CH7) will properly digitize a signal in the range of (VCC/2 – 1.25V) to (VCC/2 + 1.25V). A2-A0 (shown 00oB)(1) CH0 CH1 CH2 CH3 ±VREF(1) CHX ADS8345 CH4 COM CH5 Common-Mode Voltage (typically VREF) CH6 ± –IN VREF(1) CHX+ 2 ADS8345 (1) Common-Mode Voltage +IN Converter CH7 Single-Ended Input ± VREF 2 CHX– Differential Input NOTE: (1) Relative to common-mode voltage. COM NOTE: (1) See Truth Tables, Table I, and Table II for address coding. FIGURE 2. Methods of Driving the ADS8345—Single-Ended or Differential. 5 SGL/DIF (shown HIGH) FIGURE 4. Simplified Diagram of the Analog Input. VCC = 5V 4.9 5.2 5 4 VCC = 5V 3 2.8 2.1 2 1 0.1 0 –1 0.5 1.0 1.5 2.0 Common Voltage Range (V) Common Voltage Range (V) 4.2 4 Single-Ended Input 2.5 2 1 0.8 0.2 1.0 1.5 2.0 2.5 VREF (V) FIGURE 3. Single-Ended Input—Common Voltage Range vs VREF. SBAS177C Differential Input 0 0.0 VREF (V) ADS8345 3 FIGURE 5. Differential Input—Common Voltage Range vs VREF. www.ti.com 11 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 65536. Any offset or gain error inherent in the A/D converter will appear to increase, in terms of LSB 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, 152.8µV. Most microprocessors communicate using 8-bit transfers; the ADS8345 can complete a conversion with three such transfers, for a total of 24 clock cycles on the DCLK input, provided the timing is as shown in Figure 6. The first eight clock 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 four more clock cycles, the control byte is complete and the converter enters the conversion mode. At this point, the input sample-and-hold goes into the Hold mode. The next sixteen clock cycles accomplish the actual A/D conversion. The noise or uncertainty of the digitized output will increase with lower LSB size. With a reference voltage of 500mV, the LSB size is 15.3µV. This level is below the internal noise of the device. As a result, the digital output code will not be stable and will 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. Control Byte Figure 6 shows 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 ADS8345 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 (see Tables III and IV and Figure 4). 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 ADS8345. 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. BIT 7 (MSB) BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 (LSB) S A2 A1 A0 — SGL/DIF PD1 PD0 TABLE I. Order of the Control Bits in the Control Byte. BIT NAME 7 S Start Bit. Control byte starts with first HIGH bit on DIN. A2-A0 Channel Select Bits. Along with the SGL/DIF bit, these bits control the setting of the multiplexer input. 2 SGL/DIF Single-Ended/Differential Select Bit. Along with bits A2-A0, this bit controls the setting of the multiplexer input. 1-0 PD1-PD0 Power-Down Mode Select Bits. See Table V for details. 6-4 DIGITAL INTERFACE The ADS8345 has a 4-wire serial interface compatible with several microprocessor families (note that the digital inputs are over-voltage tolerant up to +5.5V, regardless of +VCC). Figure 6 shows the typical operation of the ADS8345 digital interface. DESCRIPTION TABLE II. Descriptions of the Control Bits within the Control Byte. CS tACQ DCLK 1 8 Idle DIN S A2 8 1 Acquire A1 A0 1 8 1 8 Conversion Idle SGL/ PD1 PD0 DIF S (START) A2 Acquire A1 A0 1 Conversion SGL/ PD1 PD0 DIF (START) BUSY DOUT 15 14 13 12 11 10 9 8 7 (MSB) 6 5 4 3 2 1 0 (LSB) Zero Filled... 15 14 (MSB) FIGURE 6. Conversion Timing, 24-Clocks per Conversion, 8-Bit Bus Interface. No DCLK delay required with dedicated serial port. 12 www.ti.com ADS8345 SBAS177C The SGL/DIF -bit controls the multiplexer input mode: either in single-ended mode, where the selected input channel is referenced to the COM pin, or in differential mode, where the two selected inputs provide a differential input. See Tables III and IV and Figure 4 for more information. The last two bits (PD1-PD0) select the Power-Down mode and Clock mode, as shown in Table V. If both PD1 and PD0 are HIGH, the device is always powered up. If both PD1 and PD0 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. A2 A1 A0 0 0 0 1 0 0 0 0 1 1 0 1 0 1 0 1 1 0 0 1 1 1 1 1 CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 COM +IN –IN +IN –IN +IN –IN +IN –IN +IN –IN +IN –IN +IN –IN +IN A1 A0 CH0 CH1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 +IN –IN –IN CH2 CH3 +IN –IN CH4 CH5 +IN –IN CH6 CH7 +IN –IN +IN –IN PD0 0 0 Power-down between conversions. When each conversion is finished, the converter enters a low-power 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. DESCRIPTION 1 0 Selects internal clock mode. 0 1 Reserved for future use. 1 1 No power-down between conversions, device always powered. Selects external clock mode. TABLE V. Power-Down Selection. Clock Modes The ADS8345 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. If the user decides to switch from one clock mode to the other, an extra conversion cycle will be required before the ADS8345 can switch to the new mode. The extra cycle is required because the PD0 and PD1 control bits need to be written to the ADS8345 prior to the change in clock modes. –IN TABLE III. Single-Ended Channel Selection (SGL/DIF HIGH). A2 PD1 When power is first applied to the ADS8345, the user must set the desired clock mode. It can be set by writing PD1 = 1 and PD0 = 0 for internal clock mode or PD1 = 1 and PD0 = 1 for external clock mode. After enabling the required clock mode, only then should the ADS8345 be set to power-down between conversions (i.e., PD1 = PD0 = 0). The ADS8345 maintains the clock mode it was in prior to entering the power-down modes. External Clock Mode +IN –IN In external clock mode, the external clock not only shifts data in and out of the ADS8345, 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 DCLK falling edges (see Figure 6). Figure 7 shows the BUSY timing in external clock mode. +IN –IN +IN TABLE IV. Differential Channel Control (SGL/DIF LOW). CS tCSS tCL tCH tBD tBD tD0 tCSH DCLK tDS DIN tDH PD0 tBDV tBTR BUSY tDV tTR DOUT 15 14 FIGURE 7. Detailed Timing Diagram. ADS8345 SBAS177C www.ti.com 13 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. 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. There are two ways of handling this requirement. One is where the beginning of the next control byte appears at the same time the LSB is being clocked out of the ADS8345 (see Figure 6). This method allows for maximum throughput and 24 clock cycles per conversion. Data can be shifted in and out of the ADS8345 at clock rates exceeding 2.4MHz, provided that the minimum acquisition time tACQ, is kept above 1.7µs. Digital Timing 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. Figure 7 and Tables VI and VII provide detailed timing for the digital interface of the ADS8345. SYMBOL DESCRIPTION MIN tACQ tDS tDH tDO tDV tTR tCSS tCSH tCH tCL tBD tBDV tBTR 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 1.5 100 10 Internal Clock Mode In internal clock mode, the ADS8345 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 a 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, DCLK 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. TYP MAX UNITS µs ns ns ns ns ns ns ns ns ns ns ns ns 200 200 200 100 0 200 200 200 200 200 TABLE VI. Timing Specifications (+VCC = +2.7V to 3.6V, TA = –40°C to +85°C, CLOAD = 50pF). CS tACQ DCLK 1 8 Idle DIN S A2 1 8 Acquire A1 A0 1 1 8 8 Conversion Idle SGL/ DIF PD1 PD0 (START) BUSY DOUT 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Zero Filled... 0 (MSB) (LSB) FIGURE 8. External Clock Mode, 32 Clocks Per Conversion. CS tACQ DCLK 1 8 Idle DIN S A2 Acquire A1 A0 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Conversion SGL/ PD1 PD0 DIF (START) BUSY DOUT 15 14 13 12 11 10 (MSB) 9 8 7 6 5 4 3 2 1 0 Zero Filled... (LSB) FIGURE 9. Internal Clock Mode Timing. 14 www.ti.com ADS8345 SBAS177C SYMBOL DESCRIPTION MIN tACQ tDS tDH tDO tDV tTR tCSS tCSH tCH tCL tBD tBDV tBTR 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 1.7 50 10 TYP MAX UNITS µs ns ns ns ns ns ns ns ns ns ns ns ns 100 70 70 50 0 150 150 100 70 70 Operating the ADS8345 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. NOISE TABLE VII. Timing Specifications (+VCC = +4.75V to +5.25V, TA = –40°C to +85°C, and CLOAD = 50pF). Data Format The output data from the ADS8345 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 error, or noise. DESCRIPTION ANALOG VALUE DIGITAL OUTPUT Full-Scale Range 2 • VREF Least Significant Bit (LSB) 2 • VREF/65536 BINARY CODE HEX CODE +Full-Scale +VREF – 1LSB 0111 1111 1111 1111 7FFF 0V 0000 0000 0000 0000 0000 0V – 1LSB 1111 1111 1111 1111 FFFF –VREF 1000 0000 0000 0000 8000 Midscale Midscale – 1LSB –Full-Scale If DCLK is active and CS is LOW while the ADS8345 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. BINARY TWO’S COMPLEMENT TABLE VIII. Ideal Input Voltages and Output Codes. The noise floor of the ADS8345 itself is rather low (see Figures 10 and 11). The ADS8345 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 ADS8345. This is true for all 16-bit, SARtype, 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 ADS8345, with 5 output codes for the ±3σ distribution, will yield a < ±0.83LSB 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. POWER DISSIPATION 3544 There are three power modes for the ADS8345: full-power (PD1-PD0 = 11B), auto power-down (PD1-PD0 = 00B), and shutdown (SHDN LOW). The effects of these modes varies depending on how the ADS8345 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 will not lower power dissipation. When operating at full-speed and 24-clocks per conversion (see Figure 6), the ADS8345 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 conversions are simply done less often, then the difference between the two modes is dramatic. In the latter case, the converter spends an increasing percentage of its time in power-down mode (assuming the auto power-down mode is active). ADS8345 SBAS177C 701 568 122 FFFEH 65 FFFFH 0000H 0001H 0002H Code FIGURE 10. Histogram of 5000 Conversions of a DC Input at the Code Transition, 5V operation external clock mode. VREF = VCOM = 2.5V. www.ti.com 15 output of the analog comparator. Thus, during any single conversion for an n-bit 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 highpower 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. 2305 938 780 436 6 435 64 FFFCH FFFDH FFFEH FFFFH 0000H 0001H 0002H 28 8 0003H 0004H With this in mind, power to the ADS8345 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. Code FIGURE 11. Histogram of 5000 Conversions of a DC Input at the Code Center, 2.7V operation external clock mode. VREF = VCOM = 1.25V. 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 signal-to-noise ratio will improve 3dB. LAYOUT For optimum performance, care should be taken with the physical layout of the ADS8345 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 16 The reference should be similarly bypassed with a 0.1µF 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 ADS8345 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 ADS8345 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. 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. www.ti.com ADS8345 SBAS177C PACKAGE DRAWINGS DBQ (R-PDSO-G**) PLASTIC SMALL-OUTLINE 24 PINS SHOWN 0.012 (0,30) 0.008 (0,20) 0.025 (0,64) 24 0.005 (0,13) M 13 0.244 (6,20) 0.228 (5,80) 0.008 (0,20) NOM 0.157 (3,99) 0.150 (3,81) 1 Gage Plane 12 A 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) 0.004 (0,10) PINS ** 16 20 24 28 A MAX 0.197 (5,00) 0.344 (8,74) 0.344 (8,74) 0.394 (10,01) A MIN 0.188 (4,78) 0.337 (8,56) 0.337 (8,56) 0.386 (9,80) DIM 4073301/E 10/00 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 ADS8345 SBAS177C www.ti.com 17 PACKAGE DRAWINGS (Cont.) DB (R-PDSO-G**) PLASTIC SMALL-OUTLINE 28 PINS SHOWN 0,38 0,22 0,65 28 0,15 M 15 0,25 0,09 8,20 7,40 5,60 5,00 Gage Plane 1 14 0,25 A 0°– 8° 0,95 0,55 Seating Plane 2,00 MAX 0,10 0,05 MIN PINS ** 14 16 20 24 28 30 38 A MAX 6,50 6,50 7,50 8,50 10,50 10,50 12,90 A MIN 5,90 5,90 6,90 7,90 9,90 9,90 12,30 DIM 4040065 /E 12/01 NOTES: A. B. C. D. 18 All linear dimensions are in millimeters. This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion not to exceed 0,15. Falls within JEDEC MO-150 www.ti.com ADS8345 SBAS177C PACKAGE OPTION ADDENDUM www.ti.com 3-Oct-2003 PACKAGING INFORMATION ORDERABLE DEVICE STATUS(1) PACKAGE TYPE PACKAGE DRAWING PINS PACKAGE QTY ADS8345E ACTIVE SSOP DBQ 20 56 ADS8345E/2K5 ACTIVE SSOP DBQ 20 2500 ADS8345EB ACTIVE SSOP DBQ 20 56 ADS8345EB/2K5 ACTIVE SSOP DBQ 20 2500 ADS8345N ACTIVE SSOP DB 20 68 ADS8345N/1K ACTIVE SSOP DB 20 1000 ADS8345NB ACTIVE SSOP DB 20 68 ADS8345NB/1K ACTIVE SSOP DB 20 1000 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. 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