Datasheet AD7713 (Analog Devices)

LC2MOS Loop-Powered Signal Conditioning ADC AD7713 FEATURES FUNCTIONAL BLOCK DIAGRAM Charge Balancing ADC 24 Bits No Missing Codes REF REF
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AVDD DVDD IN(–) IN(+) STANDBY 0.0015% Nonlinearity 3-Channel Programmable Gain Front End AVDD Gains from 1 to 128 AD7713 2 Differential Inputs 1
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A 1 Single-Ended High Voltage Input CHARGING BALANCING ADC Low-Pass Filter with Programmable Filter Cutoffs AIN1(+) AUTO-ZEROED
⌺
DIGITAL SYNC Ability to Read/Write Calibration Coefficients -
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AIN1(–) PGA MODULATOR FILTER AIN2(+) Bidirectional Microcontroller Serial Interface MUX AIN2(–) Single-Supply Operation A = 1 – 128 MCLK INPUT AIN3 SCALING CLOCK IN Low Power (3.5 mW typ) with Power-Down Mode GENERATION MCLK AV (150
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W typ) DD 200
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A OUT SERIAL INTERFACE RTD1 APPLICATIONS CONTROL OUTPUT Loop Powered (Smart) Transmitters 200
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A REGISTER REGISTER RTD Transducers RTD2 Process Control Portable Industrial Instruments AGND DGND RFS TFS MODE SDATA SCLK DRDY A0 GENERAL DESCRIPTION
CMOS construction ensures low power dissipation, and a hard- The AD7713 is a complete analog front end for low frequency ware programmable power-down mode reduces the standby measurement applications. The device accepts low level signals power consumption to only 150 µW typical. The part is available directly from a transducer or high level signals (4 ⫻ VREF) and in a 24-lead, 0.3 inch wide, PDIP and CERDIP as well as a 24- outputs a serial digital word. It employs ⌺-⌬ conversion lead SOIC package. technique to realize up to 24 bits of no missing codes performance. The input signal is applied to a proprietary pro-
PRODUCT HIGHLIGHTS
grammable gain front end based around an analog modulator. 1. The AD7713 consumes less than 1 mA in total supply current, The modulator output is processed by an on-chip digital filter. making it ideal for use in loop-powered systems. The first notch of this digital filter can be programmed via the 2. The two programmable gain channels allow the AD7713 to on-chip control register, allowing adjustment of the filter cutoff accept input signals directly from a transducer removing a and settling time. considerable amount of signal conditioning. To maximize The part features two differential analog inputs and one single- the flexibility of the part, the high level analog input accepts ended high level analog input as well as a differential reference 4 ⫻ VREF signals. On-chip current sources provide excitation input. It can be operated from a single supply (AVDD and DVDD for 3-wire and 4-wire RTD configurations. at 5 V). The part provides two current sources that can be used 3. No missing codes ensures true, usable, 24-bit dynamic range to provide excitation in 3-wire and 4-wire RTD configurations. coupled with excellent The AD7713 thus performs all signal conditioning and conver- ±0.0015% accuracy. The effects of temperature drift are eliminated by on-chip self-calibration, sion for a single-, dual- or three-channel system. which removes zero-scale and full-scale errors. The AD7713 is ideal for use in smart, microcontroller-based 4. The AD7713 is ideal for microcontroller or DSP processor systems. Gain settings, signal polarity, and RTD current control applications with an on-chip control register, which allows can be configured in software using the bidirectional serial port. control over filter cutoff, input gain, signal polarity, and The AD7713 contains self-calibration, system calibration, and calibration modes. The AD7713 allows the user to read and background calibration options and also allows the user to read write the on-chip calibration registers. and to write the on-chip calibration registers. REV. D 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 GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM PRODUCT HIGHLIGHTS SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ORDERING GUIDE PIN CONFIGURATION PIN FUNCTION DESCRIPTION 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) Filter Selection (FS11 to FS0) CIRCUIT DESCRIPTION THEORY OF OPERATION Input Sample Rate DIGITAL FILTERING Filter Characteristics Post Filtering Antialias Considerations ANALOG INPUT FUNCTIONS Analog Input Ranges Burn Out Current RTD Excitation Currents Bipolar/Unipolar Inputs REFERENCE INPUT USING THE AD7713 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 AD7713 to 8XC51 Interface AD7713 to 68HC11 Interface APPLICATIONS 4-Wire RTD Configurations 3-Wire RTD Configurations 4–20 mA Loop OTHER 24-BIT SIGNAL CONDITIONING ADCS AVAILABLE FROM ANALOG DEVICES AD7710 AD7711 AD7712 OUTLINE DIMENSIONS Revision History