AD7714* 3 V/5 V, CMOS, 500 ÂµA Signal Conditioning ADC - dreamm

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AD7714 Data Acquisition The AD7714 with its three differential channels (or five pseudodifferential channels) is suited to low bandwidth, high resolution data acquisition systems. In addition, the three-wire digital interface allows this data acquisition front end to be isolated with just three optoisolators. The entire system can be operated +5V from a single +3 V or +5 V supply provided that the input signals to the AD7714’s analog inputs are all of positive polarity. The low power operation of the AD7714 ensures that very little power has to be brought across the isolation barrier. Figure 15 shows the AD7714 in an isolated data acquisition system. AV DD DV DD AV DD 1µA AD7714 IN1+ AIN1 IN1– AIN2 AIN3 AUTO-ZEROED IN2+ ∑∆ AIN4 PGA IN2– BUFFER MODULATOR +V IN AGND REGISTER BANK IN3+ AIN5 IN3– AIN6 A = 1–128 +5V 1µA SERIAL INTERFACE AD780 GND V OUT REF IN (+) REF IN (–) AGND SWITCHING MATRIX CHARGING BALANCING A/D CONVERTER DIGITAL FILTER CLOCK GENERATION STANDBY SYNC MCLK IN MCLK OUT RESET DRDY POL DGND BUFFER DOUT DIN CS SCLK DV DD MICROCONTROLLER OPTO-ISOLATORS Figure 15. Data Acquisition System Using the AD7714 ISOLATION BARRIER MAIN TRANSMITTER ASSEMBLY ISOLATED SUPPLY 3V VOLTAGE REGULATOR DV DD AV DD REF IN VOLTAGE REFERENCE V CC VOLTAGE REFERENCE SENSORS RTD mV ohm TC AMBIENT TEMP. SENSOR AD7714 MCLK IN MCLK OUT MICROCONTROLLER UNIT *PID *RANGE SETTING *CALIBRATION *LINEARIZATION *OUTPUT CONTROL *SERIAL COMMUNICATION *HART PROTOCOL COM 3V D/A CONVERTER HART MODEM BELL 202 SIGNAL CONDITIONER WAVEFORM SHAPER INPUT/OUTPUT STAGE BANDPASS FILTER LOOP RTN 4–20mA DGND AGND COM ISOLATED GROUND Smart Transmitters Another area where the low power, single supply, three-wire interface capabilities is of benefit is in smart transmitters. Here, the entire smart transmitter must operate from the 4 mA to 20 mA loop. Tolerances in the loop mean that the amount of current available to power the transmitter is as low as 3.5 mA. Figure 16. Smart Transmitter Using the AD7714 –34– The AD7714 consumes only <strong>500</strong> µA, leaving 3 mA available for the rest of the transmitter. Figure 16 shows a block diagram of a smart transmitter which includes the AD7714. Not shown in Figure 16 is the isolated power source required to power the front end. REV. B
PAGE INDEX Topic Page FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . 1 PRODUCT HIGHLIGHTS . . . . . . . . . . . . . . . . . . . . . . . . . 1 AD7714-5 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . 2 AD7714-3 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . 3 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 TIMING CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . 5 ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . 6 PIN CONFIGURATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 6 PIN FUNCTION DESCRIPTION . . . . . . . . . . . . . . . . . . . 7 TERMINOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 AD7714-5 OUTPUT NOISE . . . . . . . . . . . . . . . . . . . . . . . . 9 AD7714-3 OUTPUT NOISE . . . . . . . . . . . . . . . . . . . . . . . 10 BUFFERED MODE NOISE . . . . . . . . . . . . . . . . . . . . . . . 11 ON-CHIP REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Communications Register . . . . . . . . . . . . . . . . . . . . . . . . 12 Mode Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Mode Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Filter Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Test Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Calibration Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 CALIBRATION OPERATION . . . . . . . . . . . . . . . . . . . . . 16 CIRCUIT DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . 17 ANALOG INPUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Analog Input Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Input Sample Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Burn-Out Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Bipolar/Unipolar Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . 19 REFERENCE INPUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 DIGITAL FILTERING . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Filter Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Post-Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 ANALOG FILTERING . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 CALIBRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Self-Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 System Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 System-Offset Calibration . . . . . . . . . . . . . . . . . . . . . . . . 23 Background Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Span and Offset Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Power-Up and Calibration . . . . . . . . . . . . . . . . . . . . . . . . 24 USING THE AD7714 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Clocking and Oscillator Circuit . . . . . . . . . . . . . . . . . . . . 24 System Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Reset Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Standby Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Drift Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 POWER SUPPLIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Supply Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Grounding and Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Evaluating the AD7714 Performance . . . . . . . . . . . . . . . . 26 DIGITAL INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 CONFIGURING THE AD7714 . . . . . . . . . . . . . . . . . . . . . 28 MICROCOMPUTER/MICROPROCESSOR INTERFACING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 AD7714 to 68HC11 Interface . . . . . . . . . . . . . . . . . . . . . 29 AD7714 to 8051 Interface . . . . . . . . . . . . . . . . . . . . . . . . 29 AD7714 to ADSP-2103/ADSP-2105 Interface . . . . . . . . 30 AD7714 Topic Page CODE FOR SETTING UP AD7714 . . . . . . . . . . . . . . . . . 30 C Code for Interfacing AD7714 to 68HC11 . . . . . . . . . . 31 APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Pressure Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Temperature Measurement . . . . . . . . . . . . . . . . . . . . . . . 32 Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Smart Transmitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . 36 TABLE INDEX Table Title Table Ia. AD7714-5 Output Noise/Resolution vs. Gain and First Notch for f CLK IN = 2.4576 MHz Table Ib. AD7714-5 Output Noise/Resolution vs. Gain and First Notch for f CLK IN = 1 MHz Table IIa. AD7714-3 Output Noise/Resolution vs. Gain and First Notch for f CLK IN = 2.4576 MHz Table IIb. AD7714-3 Output Noise/Resolution vs. Gain and First Notch for f CLK IN = 1 MHz Table III. AD7714-5 Buffered Mode Output Noise/ Resolution Table IV. AD7714-3 Buffered Mode Output Noise/ Resolution Table V. Communications Register Table VI. Register Selection Table VII. Channel Selection Table VIII. Mode Register Table IX. Filter High Register Table X. Filter Low Register Table XI. Calibration Sequences Table XII. External R, C for No 16-Bit Gain Error Table XIII. External R, C for No 20-Bit Gain Error Table XIV. Input Sampling Frequency vs. Gain Table XV. C Code for AD7714 to 68HC11 Interface 2 REV. B –35–
Page 1 and 2: a FEATURES Charge Balancing ADC 24
Page 3 and 4: AD7714-3-SPECIFICATIONS (AV DD = +3
Page 5 and 6: TIMING CHARACTERISTICS 1, 2 (AV DD
Page 7 and 8: AD7714 DIP/SOIC PIN NUMBERS PIN FUN
Page 9 and 10: AD7714 AD7714-5 OUTPUT NOISE Table
Page 11 and 12: AD7714 BUFFERED MODE NOISE Table II
Page 13 and 14: CH2-CH0 AD7714 Channel Select. Thes
Page 15 and 16: AD7714 Filter Registers. Power On/R
Page 17 and 18: CIRCUIT DESCRIPTION The AD7714 is a
Page 19 and 20: AD7714 Gain Table XIV. Input Sampli
Page 21 and 22: ANALOG FILTERING The digital filter
Page 23 and 24: System-Offset Calibration System-of
Page 25 and 26: The SYNC input can also be used as
Page 27 and 28: no longer corresponds to a full-sca
Page 29 and 30: AD7714 MICROCOMPUTER/MICROPROCESSOR
Page 31 and 32: AD7714 TABLE XV. C CODE FOR INTERFA
Page 33: AD7714 +5V AV DD DV DD THERMOCOUPLE

AD7714* 3 V/5 V, CMOS, 500 ÂµA Signal Conditioning ADC - dreamm

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