SBOS051F October   1995  – May 2022 INA128 , INA129

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 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. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Noise Performance
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Input Common-Mode Range
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Setting the Gain
        2. 9.2.2.2 Dynamic Performance
        3. 9.2.2.3 Offset Trimming
        4. 9.2.2.4 Input Bias Current Return Path
      3. 9.2.3 Application Curves
    3. 9.3 System Examples
  10. 10Power Supply Recommendations
    1. 10.1 Low-Voltage Operation
  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. 12.1.1.1 PSpice® for TI
        2. 12.1.1.2 TINA-TI™ Simulation Software (Free Download)
    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

9.2.2.4 Input Bias Current Return Path

The input impedance of the INA12x is extremely high: approximately 10 GΩ. However, a path must be provided for the input bias current of both inputs. This input bias current is approximately ±2 nA. High input impedance means that this input bias current changes very little with varying input voltage.

Input circuitry must provide a path for this input bias current for proper operation. Figure 9-3 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, and the input amplifiers saturate.

If the differential source resistance is low, the bias current return path can be connected to one input (see the thermocouple example in Figure 9-3). With higher source impedance, use two equal resistors to provide a balanced input, with possible advantages of lower input offset voltage due to bias current, and better high-frequency common-mode rejection.

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-F3F18901-124B-465F-8511-93B53F6DA203-low.gif Figure 9-3 Providing an Input Common-Mode Current Path