SBOU246 January   2022 TMP61 , TMP61-Q1 , TMP63 , TMP63-Q1 , TMP64 , TMP64-Q1

 

  1.   Trademarks
  2. 1Introduction
    1. 1.1 NTC Thermistor Versus TMP6 Linear Thermistor Family
    2. 1.2 NTC/Linear Thermistor TCR
    3. 1.3 NTC Versus Silicon-Based Linear Thermistor Trade-Offs
    4. 1.4 TMP6 Accuracy
  3. 2Typical NTC Thermistor Design Considerations
    1. 2.1 Voltage-Biased NTC Thermistor Network
    2. 2.2 Pinouts/Polarity
    3. 2.3 Converting NTC Thermistor Hardware Design to TMP6 Linear Thermistor Design
    4. 2.4 Simple Look-Up Table
  4. 3Software Changes
    1. 3.1 Firmware Design Considerations
    2. 3.2 Oversampling
    3. 3.3 Low-Pass Filtering in HW Versus SW
    4. 3.4 Calibration
  5. 4Design considerations for Full-Scale Range Voltage Output
    1. 4.1 Simple Current-Biased
    2. 4.2 Active Voltage-Biased
  6. 5Conclusion
  7. 6Additional Resources/Considerations
    1. 6.1 Constant-Current Source Design
    2. 6.2 TMP6 Thermistor Standard Component Footprints
    3. 6.3 Dual-Sourcing Approach for TMP6 and NTC Thermistors

1.2 NTC/Linear Thermistor TCR

The temperature coefficient resistance (TCR) can be defined as the change in resistance as temperature changes for a device. Use Equation 1 to calculate the TCR measured in ppm/°C.

Equation 1. Temperature Characteristic Resistance = ((R2–R1)/R1×(T2–T1))×10^6

Due to the linearity of the TMP61 thermistor, the device has a consistent TCR across a wide operating temperature range. Unlike an NTC thermistor, which is a purely resistive device, the TMP61 thermistor's effective resistance is affected by the current across the device and the effective resistance changes when the temperature changes. The TMP61 thermistor has a 6400 ppm/°C TCR (25°C) with a 0.2% typical TCR tolerance across the entire temperature range. However, this value does vary slightly depending on how the TMP61 thermistor is biased.

The TMP6 thermistor has many advantages while the NTC thermistor, at first glance, has an advantage of change in resistance at room temperature. The TMP6 thermistor can achieve the same or better accuracy with simple enhancements that TI provides.