SBOA505 December   2020 OPA2991-Q1 , TLV197-Q1 , TLV2197-Q1 , TLV4197-Q1 , TMP61 , TMP61-Q1 , TMP63 , TMP63-Q1 , TMP64-Q1

 

  1.   Design Goals
  2.   Design Description
  3.   Design Notes
  4.   Design Information
  5.   Design Steps
  6.   Design Simulations
  7.   DC Simulation Results
  8.   Sensor Circuit Accuracy Using a Linear Approximation
  9.   Improving Accuracy of the Sensor Circuit
  10.   Design References
  11.   Design Featured Op Amp
  12.   Design Alternate Op Amp

Design Notes

  1. Use the op amp in a linear operating region. Linear output swing is usually specified under the AOL test conditions.

  2. Choose R1 based on the temperature range and the value of the PTC.

  3. Using high-value resistors can degrade the phase margin of the amplifier and introduce additional noise in the circuit. It is recommended to use resistor values around 10kΩ or less.

  4. A capacitor placed in parallel with the feedback resistor will limit bandwidth, improve stability and help reduce noise.

  5. Typical resistance values are selected from the PTC resistor resistance characteristics across temperature. Take consideration for the minimum and maximum resistance limits of the PTC resistor, per temperature.

  6. For single op-amp supply conditions, the output cannot swing exactly to 0V but can swing to 5V utilizing the 12-V supply. Increase VoutMin to the linear output swing usually specified under the AOL test conditions to improve accuracy.