Datasheet AD7710 (Analog Devices)

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Signal Conditioning ADC AD7710 FEATURES FUNCTIONAL BLOCK DIAGRAM Charge Balancing ADC REF REF 24 Bits, No Missing Codes AV IN (–) IN (+) V REF OUT DD DVDD BIAS
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0.0015% Nonlinearity AV 2-Channel Programmable Gain Front End DD Gains from 1 to 128 2.5V REFERENCE 4.5
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A Differential Inputs CHARGE-BALANCING A/D Low-Pass Filter with Programmable Filter Cutoffs CONVERTER AIN1(+) Ability to Read/Write Calibration Coefficients AUTO-ZEROED AIN1(–) M PGA DIGITAL SYNC Bidirectional Microcontroller Serial Interface
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FILTER U MODULATOR AIN2(+) Internal/External Reference Option X A = 1 – 128 Single- or Dual-Supply Operation AIN2(–) MCLK Low Power (25 mW Typ) with Power-Down Mode AV CLOCK IN DD GENERATION (7 mW Typ) MCLK OUT 20
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A SERIAL INTERFACE APPLICATIONS CONTROL Weigh Scales OUTPUT IOUT REGISTER REGISTER Thermocouples AD7710 Process Control Smart Transmitters Chromatography AGND DGND V RFS TFS MODE SDATA SCLK DRDY A0 SS GENERAL DESCRIPTION
The AD7710 is a complete analog front end for low frequency CMOS construction ensures low power dissipation, and a soft- measurement applications. The device accepts low level signals ware programmable power-down mode reduces the standby directly from a strain gage or transducer and outputs a serial power consumption to only 7 mW typical. The part is available digital word. It employs a sigma-delta conversion technique to in a 24-lead, 0.3 inch-wide, plastic and hermetic dual-in-line realize up to 24 bits of no missing codes performance. The input package (DIP) as well as a 24-lead small outline (SOIC) package. signal is applied to a proprietary programmable gain front end based around an analog modulator. The modulator output is
PRODUCT HIGHLIGHTS
processed by an on-chip digital filter. The first notch of this 1. The programmable gain front end allows the AD7710 to digital filter can be programmed via the on-chip control register, accept input signals directly from a strain gage or transducer, allowing adjustment of the filter cutoff and settling time. removing a considerable amount of signal conditioning. The part features two differential analog inputs and a differen- 2. The AD7710 is ideal for microcontroller or DSP processor tial reference input. Typically, one of the channels will be used applications with an on-chip control register that allows as the main channel with the second channel used as an auxil- control over filter cutoff, input gain, channel selection, signal iary input to measure a second voltage periodically. It can be polarity, and calibration modes. operated from a single supply (by tying the VSS pin to AGND), provided that the input signals on the analog inputs are more 3. The AD7710 allows the user to read and write the on-chip positive than –30 mV. By taking the V calibration registers. This means that the microcontroller has SS pin negative, the part can convert signals down to –V much greater control over the calibration procedure. REF on its inputs. The AD7710 thus performs all signal conditioning and conversion for a single- 4. No missing codes ensures true, usable, 23-bit dynamic range or dual-channel system. coupled with excellent ± 0.0015% accuracy. The effects of The AD7710 is ideal for use in smart, microcontroller based temperature drift are eliminated by on-chip self-calibration, systems. Input channel selection, gain settings, and signal polar- which removes zero-scale and full-scale errors. ity can be configured in software using the bidirectional serial port. The AD7710 contains self-calibration, system calibration, and background calibration options, and also allows the user to read and write the on-chip calibration registers. REV. G Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise
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Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION PRODUCT HIGHLIGHTS SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS TIMING CHARACTERISTICS ORDERING GUIDE PIN CONFIGURATION PIN FUNCTION DESCRIPTIONS Terminology Integral Nonlinearity Positive Full-Scale Error Unipolar Offset Error Bipolar Zero Error Bipolar Negative Full-Scale Error Positive Full-Scale Overrange Negative Full-Scale Overrange Offset Calibration Range Full-Scale Calibration Range Input Span CONTROL REGISTER (24 BITS) PGA GAIN CHANNEL SELECTION Power-Down Word Length Output Compensation Current Burn-Out Current Bipolar/Unipolar Selection (Both Inputs) FILTER SELECTION (FS11–FS0) CIRCUIT DESCRIPTION THEORY OF OPERATION Input Sample Rate DIGITAL FILTERING Filter Characteristics Post Filtering Antialias Considerations ANALOG INPUT FUNCTIONS Analog Input Ranges Burnout Current Output Compensation Current Bipolar/Unipolar Inputs REFERENCE INPUT/OUTPUT VBIAS Input USING THE AD7710 SYSTEM DESIGN CONSIDERATIONS Clocking System Synchronization Accuracy Autocalibration Self-Calibration System Calibration System Offset Calibration Background Calibration Span and Offset Limits POWER-UP AND CALIBRATION Drift Considerations POWER SUPPLIES AND GROUNDING DIGITAL INTERFACE Self-Clocking Mode Read Operation Write Operation External Clocking Mode Read Operation Write Operation SIMPLIFYING THE EXTERNAL CLOCKING MODE INTERFACE MICROCOMPUTER/MICROPROCESSOR INTERFACING AD7710 to 8XC51 Interface AD7710 to 68HC11 Interface APPLICATIONS OUTLINE DIMENSIONS Revision History