ADS8661 Datasheet, PDF (20/71 Pages) Texas Instruments – 12-Bit, High-Speed, Single-Supply, SAR ADC Data Acquisition System with Programmable, Bipolar Input Ranges

ADS8661, ADS8665
SBAS780 – DECEMBER 2016
7 Detailed Description
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7.1 Overview
The ADS866x devices belong to a family of high-speed, high-performance, easy-to-use integrated data
acquisition system. This single-channel device supports true bipolar input voltage swings up to ±12.288 V,
operating on a single 5-V analog supply. The device features an enhanced SPI interface (multiSPI) that allows
the sampling rate to be maximized even with lower speed host controllers.
The device consists of a high-precision successive approximation register (SAR) analog-to-digital converter
(ADC) and a power-optimized analog front-end (AFE) circuit for signal conditioning that includes:
• A high-resistive input impedance (≥ 1 MΩ) that is independent of the sampling rate
• A programmable gain amplifier (PGA) with a pseudo-differential input configuration supporting nine software-
programmable unipolar and bipolar input ranges
• A second-order, low-pass antialiasing filter
• An ADC driver amplifier that ensures quick settling of the SAR ADC input for high accuracy
• An input overvoltage protection circuit up to ±20 V
The device also features a low temperature drift, 4.096-V internal reference with a fast-settling buffer and a
multiSPI serial interface with daisy-chain (DAISY) and ALARM features.
The integration of the multichannel precision AFE circuit with high input impedance and a precision ADC
operating from a single 5-V supply offers a simplified end solution without requiring external high-voltage bipolar
supplies and complicated driver circuits.
7.2 Functional Block Diagram
AVDD
ADS866x
DVDD
4.096-V
Reference
REFIO
REFCAP
AIN_P
AIN_GND
1 M:
1 M:
OVP
OVP
PGA
AGND
2^nd-Order
LPF
ADC
Driver
V_BIAS
Oscillator
12-Bit
SAR ADC
Digital Logic
and Interface
CONVST/CS
SCLK
SDI
SDO
DGND
REFGND
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