SLVSL42C January   2026  – July 2026 OPA2486 , OPA486

PRODMIX  

  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 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information for OPA486
    5. 5.5 Thermal Information for OPA2486
    6. 5.6 Thermal Information for OPA4486
    7. 5.7 Electrical Characteristics
    8. 5.8 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 Input Common-Mode Range
      2. 6.3.2 Phase-Reversal Protection
      3. 6.3.3 Chopping Transients
      4. 6.3.4 EMI Rejection
      5. 6.3.5 Electrical Overstress
      6. 6.3.6 MUX-Friendly Inputs
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Basic Noise Calculations
    2. 7.2 Typical Applications
      1. 7.2.1 Instrumentation Amplifier
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
        3. 7.2.1.3 Application Curve
      2. 7.2.2 Low Power Instrumentation Amplifier
      3. 7.2.3 Difference Amplifier
      4. 7.2.4 Resistance Temperature Detector (RTD)
    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™ Simulation Software (Free Download)
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.2.1.2 Detailed Design Procedure

Designing an instrumentation amplifier with high gain and high common-mode rejection requires the use of three channels of OPAx486, and a precision matched resistor network. The instrumentation amplifier configuration is illustrated in Figure 7-3.

The strain gauge in this example is set to have a nominal resistance of 350Ω and assumed to vary up to ±6% of the nominal resistance. The variation amounts to a resistance change of about 21Ω from the nominal value. The change in resistance directly affects the full-scale output of the bridge. Using a high precision op amp with very low drift is crucial to preserve accuracy of the system. Note that bridge sensors are inherently nonlinear, but the linearity is acceptable across small changes. Figure 7-4 shows a simulated bridge output to illustrate the small nonlinearity.

OPA2486 OPA486 OPA4486 Bridge Sensor Linearity Figure 7-4 Bridge Sensor Linearity

The bridge excitation voltage also affects the full-scale output of the bridge with higher voltages producing a larger signal. The maximum voltage is limited by the manufacturer maximum rating for the bridge. Consider that an increasing voltage also leads to increased power loss across the bridge. Use a resistor to limit the current through the bridge to an acceptable level, but note that this resistor sets the common-mode voltage and reduces the overall output of the bridge. In this case, a 5V supply is readily available, and we add a resistor to limit the current through the bridge to about 3mA. The additional resistor sets the common-mode voltage of the signal to about 4.485V.

The common-mode voltage of the OPAx486 is (V−) to (V+) − 2V. To accommodate this limitation, the amplifiers are powered with a common 12V supply. The expected common-mode voltage of the bridge is within the 0V to 13V range in this application.

Equally important is consideration for the output swing voltage. In this application, there are two important considerations. The first is the output voltage limitations of the amplifiers interfacing with the bridge. Those two amplifiers need to be able to swing well above the common-mode voltage. The second consideration relates to the output amplifier. Keep the output of the amplifier within the linear output range. The OPAx486 maintains high linearity within (V−) + 0.6 to (V+) − 0.6V when driving a 10kΩ. This circuit is designed to swing from 600mV to 4.4V.

Next, determine the gain of the instrumentation amplifier using the expected output from the bridge and the output swing constraints discussed earlier. Equation 12 provides a calculation for the gain. Note that a slightly lower than calculated gain of 124V/V is chosen for this design.

Equation 12. G d i f f = 4.4 V - 0.6 V 0.015 V - - 0.015 ≈ 126 V V

This circuit provides excellent design flexibility when compared to monolithic instrumentation amplifiers. For this design, the gain is set in the first stage by resistors, RG, and RF1, and RF2. Equation 13 provides the gain equation for this amplifier. Using the value for gain obtained in Equation 12, the appropriate resistors can be chosen. Always take into account the impact on noise and stability when choosing large resistors. Make sure that resistors are tightly matched to maintain high common-mode rejection, and low gain error.

Equation 13. G d i f f = 1 + 2 R F R G

This design can be customized for any particular design taking into consideration the limitations posed in this section.