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

Oversampling

Oversampling and averaging temperature measurements in a first-in-first-out (FIFO) sequence can improve measurement resolution and signal-to-noise ratio. This is recommended when using less than a 12-bit ADC, although it can applied to 12-bit or 14-bit ADCs, as well. After the ADC reads the bit value and your code calculates the temperature, you can store that value in an array. As a new value comes into the array, the oldest sample is dropped as all the other samples are shifted to the next corresponding cell, thus creating a FIFO. The averaging method can be applied to any of the values used in temperature conversion such as the temperature, the ADC bit value, the divider voltage, or even the calculated resistance. For every 8 oversamples the resolution will increase by 2 bits. 16 oversamples will increase a 10-bit ADC to 14 bits of resolution. The figures below demonstrate two methods on how the oversampling can be implemented. See the Averaging tab of the Thermistor Design Tool for more information.

GUID-02CDBDD6-F503-47A5-B7D4-4E4BCEB3B673-low.pngFigure 3-3 Oversampling Method 1.
GUID-1E1F684A-D0BB-4D2D-B061-E28FFD19D616-low.pngFigure 3-4 Oversampling Method 2.
An example of the C code for Method 1 provided from the Thermistor Design Tool can be seen in Figure 3-5.

GUID-ADD2B73D-7B1E-44FD-8484-B7DA78A0F850-low.pngFigure 3-5 Oversampling Example C Code.
Figure 3-6 and Figure 3-7 below you can see the impact of filtering the TMP6331 Thermistor's raw data using as 12-bit ADC. After a 32x oversample, the data aligns with the reference probe more closely.

GUID-143B2D79-01D8-46AB-B0D5-BD546FE22F13-low.pngFigure 3-6 TMP6331 Thermistor Data With No Oversampling.
GUID-CE42A2F2-6FA7-4208-B951-75DA2BD68D6B-low.pngFigure 3-7 TMP6331 Thermistor Data With 32x Oversampling Applied.