SBOSA75B July   2021  – November 2021 INA823


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Gain-Setting Function
        1. Gain Drift
      2. 8.3.2 Input Common-Mode Voltage Range
      3. 8.3.3 Input Protection
    4. 8.4 Device Functional Modes
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Input Bias Current Return Path
    2. 9.2 Typical Applications
      1. 9.2.1 Resistive-Bridge Pressure Sensor
        1. Design Requirements
        2. Detailed Design Procedure
        3. Application Curves
      2. 9.2.2 Supporting High Common-Mode Voltage in PLC Input Modules
        1. Design Requirements
        2. Detailed Design Procedure
        3. Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
        1. PSpice® for TI
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Support Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Input Bias Current Return Path

The input impedance of the INA823 is extremely high, but a path must be provided for the input bias current of both inputs. This input bias current is typically 1.2 nA. High input impedance means that this input bias current changes little with varying input voltage.

For proper operation, input circuitry must provide a path for this input bias current. Figure 9-1 shows various provisions for an input bias current path. Without a bias current path, the inputs float to a potential that exceeds the common-mode range of the INA823, and the input amplifiers saturate. If the differential source resistance is low, the bias current return path connects to one input (as shown in the thermocouple example in Figure 9-1). With a higher source impedance, use two equal resistors to provide a balanced input, with the possible advantages of a lower input offset voltage as a result of bias current, and better high-frequency common-mode rejection. Furthermore, matched input impedances generally minimize the impact to performance in cases where the input common-mode voltage is very low and input bias current can increase as the IB cancellation circuity runs out of headroom. The input offset current typically remains low; therefore, well-matched input impedances reduce the differential error voltage that would otherwise arise.

For more details about why a valid input bias current return path is necessary, see the Importance of Input Bias Current Return Paths in Instrumentation Amplifier Applications application note.

GUID-410F4BC6-B25C-4DDB-A062-0A86578433F6-low.gif Figure 9-1 Providing an Input Common-Mode Current Path