SBAU427 July   2025 ADS131E08

 

  1.   1
  2.   Description
  3.   Get Started
  4.   Features
  5.   Applications
  6.   6
  7. 1Evaluation Module Overview
    1. 1.1 Introduction
    2. 1.2 Kit Contents
    3. 1.3 Device Information
    4. 1.4 Specification
  8. 2Hardware
    1. 2.1 EVM Analog Inputs
    2. 2.2 Power Supplies
    3. 2.3 ADC Connections and Decoupling
    4. 2.4 Voltage Reference
    5. 2.5 Op Amp Common-Mode Bias
    6. 2.6 Digital Interface
    7. 2.7 EEPROM
  9. 3Software
    1. 3.1 Software Description
    2. 3.2 Software Installation
  10. 4Implementation Results
    1. 4.1 Hardware Connections
    2. 4.2 Optional EVM Configuration
    3. 4.3 GUI Software Operation
      1. 4.3.1 EVM Register Settings
      2. 4.3.2 GUI Settings for ADC Control
      3. 4.3.3 Time Domain Display
      4. 4.3.4 Frequency Domain Display
      5. 4.3.5 Histogram Display
  11. 5Hardware Design Files
    1. 5.1 Schematics
    2. 5.2 PCB Layouts
    3. 5.3 Bill of Materials (BOM)
  12. 6Additional Information
    1. 6.1 Trademarks

2.5 Op Amp Common-Mode Bias

The analog input network must be biased to mid-supply because the EVM only supports a unipolar-supply analog configuration (AVSS = 0V, AVDD = 2.7V to 5.5V). The ADS131E08 includes an internal op amp whose output can be used as a common-mode bias voltage [(AVDD + AVSS) / 2] when using a unipolar power supply.

The EVM includes a buffer for the integrated op amp because this op amp has very limited current sink and source capability. Figure 2-5 shows the buffer circuitry that uses an OPA320.

Generate the common-mode bias voltage from the ADS131E08 by configuring the internal op amp in a unity-gain configuration using the feedback resistor (R24) and setting the OPAMP_REF bit of the CONFIG3 register to 1. Alternatively, generate the common-mode bias voltage externally with a resistor divider network between the positive and negative supplies.

Access the op amp output through terminal block J11.

Reference the Voltage Sensing section of the ADS131E08 data sheet for additional information and application examples regarding how to implement the op amp common-mode bias voltage reference.

ADS131E08EVM-PDK Op Amp Bias Reference CircuitFigure 2-5 Op Amp Bias Reference Circuit