AVDD

AVDD

OPA365

VIN

GND

VDD

Device

Input Driver

Device: 12-Bit, 1-MSPS,

Single-Ended Input

GND

33

+

±

+

680 pF

VSOURCE

±

Copyright © 2016, Texas Instruments Incorporated

16

ADS7886

SLAS492B – SEPTEMBER 2005 – REVISED AUGUST 2016

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Product Folder Links: ADS7886

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Copyright © 2005–2016, Texas Instruments Incorporated

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The primary circuits required to maximize the performance of a high-precision, successive approximation register

(SAR), analog-to-digital converter (ADC) are the input driver and the reference driver circuits. This section details

some general principles for designing the input driver circuit, reference driver circuit, and provides some

application circuits designed for the ADS7886.

9.2 Typical Application

Figure 29. Typical Data Acquisition (DAQ) Circuit: Single-Supply DAQ

9.2.1 Design Requirements

The goal of this application is to design a single-supply digital acquisition (DAQ) circuit based on the ADS7886

with SNR greater than 72.5 dB and THD less than –84 dB for input frequencies of 2 kHz to 100 kHz at a

throughput of 1 MSPS.

9.2.2 Detailed Design Procedure

To achieve a SINAD of 61 dB, the operational amplifier must have high bandwidth to settle the input signal within

the acquisition time of the ADC. The operational amplifier must have low noise to keep the total system noise

below 20% of the input-referred noise of the ADC. For the application circuit shown in Figure 29, OPA365 is

selected for its high bandwidth (50 MHz) and low noise (4.5 nV

√Hz).

The reference voltage for the ADS7887 and ADS7888 A/D converters are derived from the supply voltage

internally. The supply to these converters must be driven with a low impedance source and must be decoupled to

the ground. To drive supply pin of ADS7887 ultra-low noise fast transient response low dropout voltage regulator

TPS73201 is selected. Alternatively one can drive supply pin with low impedance voltage reference similar to

REF3030.

For a step-by-step design procedure for low power, small form factor digital acquisition (DAQ) circuit based on

similar SAR ADCs, see TI Precision Design, Three 12-Bit Data Acquisition Reference Designs Optimized for Low

Power and Ultra-Small Form Factor (TIDU390).