SBOS069A October   1997  – December 2024 INA122

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 Recommended Operating Conditions
    3. 5.3 Thermal Information
    4. 5.4 Electrical Characteristics
    5. 5.5 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Setting the Gain
      2. 6.3.2 Input Common-Mode Range
      3. 6.3.3 Input Protection
      4. 6.3.4 Output Current Range
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Offset Trimming
      2. 7.1.2 Input Bias Current Return Path
    2. 7.2 Typical Application
      1. 7.2.1 Resistive-Bridge Pressure Sensor
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
        3. 7.2.1.3 Application Curve
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 PSpice® for TI
        2. 8.1.1.2 TINA-TI (Free Software Download)
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • D|8
  • P|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.2.1 Resistive-Bridge Pressure Sensor

The INA122 is an instrumentation amplifier that measures small differential voltages while simultaneously rejecting larger common-mode voltages. The device offers a low power consumption of 60µA (typical) and is designed for portable applications where sensors measure physical parameters, such as changes in fluid, pressure, temperature, or humidity.

The pressure sensor is made of a piezo-resistive element that can be derived as a classical 4-resistor Wheatstone bridge. Changes in the strain gauge resistance on one leg of the Wheatstone bridge (R + ΔR) induces a differential voltage VDIFF.

Figure 7-3 shows an example circuit for a pressure sensor application. The signal chain connected to the bridge downstream processes the pressure change and can trigger an alarm.

INA122 Resistive-Bridge Pressure Sensor Figure 7-3 Resistive-Bridge Pressure Sensor

Low-tolerance bridge resistors must be used to minimize the offset and gain errors.

Given that there is only a positive differential voltage applied, this circuit is laid out in single supply mode. The excitation voltage, VEXT, to the bridge must be precise and stable; otherwise, measurement errors can be introduced.