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

6.1 Overview

The INA122 is a monolithic, precision instrumentation amplifier incorporating a two-op-amp design, providing savings in power consumption and designed for portable instrumentation and data acquisition systems. An external gain resistor (RG) sets the gain from 5V/V to 10000V/V.

Figure 6-1 shows a simplified circuit diagram of the INA122. The design of A1 and A2 are identical and both internal outputs can swing to within approximately 100mV of the power supply rails, depending on load conditions. When the output of A2 is saturated, A1 can still be in linear operation, responding to changes in the noninverting input voltage. This can give the appearance of linear operation but the output voltage is invalid.

The most commonly overlooked overload condition occurs by attempting to exceed the output swing of A2, an internal circuit node that cannot be measured. Calculating the expected voltages at output of A2 (see the equation in Figure 6-1) provides a check for the most common overload conditions.

A single supply instrumentation amplifier has special design considerations. Using commonly available single supply op amps to implement the two op amp topology cannot yield equivalent performance. For example, consider the condition where both inputs of common single supply op amps are equal to 0V. The outputs of both A1 and A2 must be 0V. But any small positive voltage applied to V+IN requires that A2 output must swing below 0V, which is not feasible without a negative power supply.

To achieve common-mode range that extends to single supply ground, the INA122 uses precision level-shifting buffers on the inputs. This shifts both inputs by approximately 0.5V, and through the feedback network, shifts A2 output by approximately 0.6V. With both inputs and VREF at single supply, A2 output operates within linear range. A positive V+IN causes A2 output to swing below 0.6V. As a result of the input level-shifting, the voltages at RG pins (pins 1 and 8) are not equal to the respective input pin voltages (pins 2 and 3). For most applications, this is not important because only the gain-setting resistor connects to RG pins.