ADS8664 Datasheet, PDF (22/79 Pages) Texas Instruments – 4- and 8-Channel, Single-Supply, SAR ADCs

ADS8664, ADS8668
SBAS492 – JULY 2015
8 Detailed Description
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8.1 Overview
The ADS8664 and ADS8668 are 12-bit data acquisition systems with 4- and 8-channel analog inputs,
respectively. Each analog input channel consists of an overvoltage protection circuit, a programmable gain
amplifier (PGA), and a second-order, antialiasing filter that conditions the input signal before being fed into a 4-
or 8-channel analog multiplexer (MUX). The output of the MUX is digitized using a 12-bit analog-to-digital
converter (ADC), based on the successive approximation register (SAR) architecture. This overall system can
achieve a maximum throughput of 500 kSPS, combined across all channels. The devices feature a 4.096-V
internal reference with a fast-settling buffer and a simple SPI-compatible serial interface with daisy-chain (DAISY)
and ALARM features.
The devices operate from a single 5-V analog supply and can accommodate true bipolar input signals up to
±2.5 × V_REF. The devices offer a constant 1-MΩ resistive input impedance irrespective of the sampling frequency
or the selected input range. The integration of multichannel precision analog front-end circuits 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.
8.2 Functional Block Diagram
AVDD
DVDD
AIN_0P
AIN_0GND
1 M:
1 M:
OVP
OVP
AIN_1P
AIN_1GND
1 M:
1 M:
OVP
OVP
AIN_2P
AIN_2GND
1 M:
1 M:
OVP
OVP
AIN_3P
AIN_3GND
1 M:
1 M:
OVP
OVP
AIN_4P
AIN_4GND
1 M:
1 M:
OVP
OVP
AIN_5P
AIN_5GND
1 M:
1 M:
OVP
OVP
AIN_6P
AIN_6GND
1 M:
1 M:
OVP
OVP
AIN_7P
AIN_7GND
1 M:
1 M:
OVP
OVP
AUX_IN
AUX_GND
PGA
2nd-Order
LPF
ADC
Driver
VB0
PGA
2nd-Order
LPF
ADC
Driver
VB1
PGA
2nd-Order
LPF
ADC
Driver
VB2
PGA
2nd-Order
LPF
ADC
Driver
VB3
PGA
2nd-Order
LPF
ADC
Driver
VB4
PGA
2nd-Order
LPF
ADC
Driver
VB5
PGA
2nd-Order
LPF
ADC
Driver
VB6
PGA
2nd-Order
LPF
ADC
Driver
VB7
ADS8668
ADS8664
Digital
Logic
and
Interface
12-Bit
SAR ADC
Oscillator
CS
SCLK
SDI
SDO
DAISY
REFSEL
RST/PD
ALARM
REFCAP
REFIO
4.096-V
Reference
22
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AGND
DGND
REFGND
Product Folder Links: ADS8664 ADS8668
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