Features and Benefits
- Charge Balancing ADC
24 Bits No Missing Codes
- High Level and Low Level Analog Input Channels
- Programmable Gain for Both Inputs
Gains from 1 to 128
Differential Input for Low Level Channel
- Low-Pass Filter with Programmable Filter Cutoffs
- Ability to Read/Write Calibration Coefficients
- Bidirectional Microcontroller Serial Interface
- Internal/External Reference Option
- Single- or Dual-Supply Operation
- Low Power (25 mW typ) with Power-Down Mode (100 µW typ)
The AD7712 is a complete analog front end for low frequency measurement applications. The device has two analog input channels and accepts either low level signals directly from a transducer or high level (±4 × VREF) signals and outputs a serial digital word. It employs a sigma-delta conversion technique to realize up to 24 bits of no missing codes performance. The low level input signal is applied to a proprietary programmable gain front end based around an analog modulator. The high level analog input is attenuated before being applied to the same modulator. The modulator output is processed by an on-chip digital filter. The first notch of this digital filter can be programmed via the on-chip control register allowing adjustment of the filter cutoff and settling time.
Normally, one of the channels will be used as the main channel with the second channel used as an auxiliary input to periodically measure a second voltage. The part can be operated from a single supply (by tying the VSS pin to AGND) provided that the input signals on the low level analog input are more positive than -30 mV. By taking the VSS pin negative, the part can convert signals down to -VREF on this low level input. This low level input, as well as the reference input, features differential input capability.
The AD7712 is ideal for use in smart, microcontroller-based systems. Input channel selection, gain settings and signal polarity can be configured in software using the bidirectional serial port. The AD7712 also contains self-calibration, system calibration and background calibration options and also allows the user to read and to write the on-chip calibration registers.
CMOS construction ensures low power dissipation and a hardware programmable power-down mode reduces the standby power consumption to only 100 µW typical. The part is available in a 24-pin, 0.3 inch wide, plastic and hermetic dual-in-line package (DIP) as well as a 24-lead small outline (SOIC) package.
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Evaluation Kits (1)
This converter utilizes sigma-delta techniques to offer 16-bit accuracy (0.0015% FSR) and no missing codes to 24-bits. It contains a two-channel programmable gain front end, a programmable low-pass digital filter and a bidirectional serial interface. One of the analog inputs and the reference input are differential and the part can accept inputs as low as 20 mV full-scale on this differential analog input. The second analog input contains an input attenuation circuit and can accept inputs up to ±10V. The part features a self-calibration mode, which removes internal offset and gain errors, a system calibration mode, which removes external circuit offset and gain errors, and a background calibration mode which automatically removes internal offset and gain errors. In addition, its flexible serial interface allows the AD7712 to connect directly to Digital Signal Processors (ADSP-2101, TMS320C25, etc.) and Microcontrollers (8XC51, 68HC11, etc.). Full data on the AD7712 is available in the AD7712 data sheet available from Analog Devices and should be consulted in conjunction with this Technical Note when using the Evaluation Board.
Documentation & Resources
AN-202: An IC Amplifier User’s Guide to Decoupling, Grounding, and Making Things Go Right for a Change (Rev. B)2/14/2015
AN-389: Using Sigma-Delta Converters-Part 22/14/2015
AN-388: Using Sigma-Delta Converters-Part 12/14/2015
AN-311: How to Reliably Protect CMOS Circuits Against Power Supply Overvoltaging3/8/2008
AN-607: Selecting a Low Bandwidth (<15 kSPS) Sigma-Delta ADC (Rev. E)10/12/2006
AN-615: Peak-to-Peak Resolution Versus Effective Resolution (Rev. 0)12/21/2004
AN-397: Electrically Induced Damage to Standard Linear Integrated Circuits:11/18/2002
AN-283: Sigma-Delta ADCs and DACs9/24/2002
AN-553: Adjusting the Calibration Coefficients on the AD771X Family of ADCs1/1/2000
AN-406: Using the AD771X Family of 24-Bit Sigma-Delta A/D Converters1/1/2000
Designing Power Supplies for High Speed ADC2/1/2012
Delta-Sigma Rocks RF, As ADC Designers Jump On Jitter1/12/2006
Part 2: Circuit Suggestions Using Features and Functionality of New Sigma-Delta ADCs6/1/2002
Part 1: Circuit Suggestions Using Features and Functionality of New Sigma-Delta ADCs10/1/2001
Design Ideas for Sigma-Delta Instrumentation ADCs4/1/1993 Analog Dialogue
Software & Systems Requirements
AD7712 Code Examples
Tools & Simulations
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