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

4.1 Simple Current-Biased

A superior configuration of the TMP61 linear thermistor is to use a current-biased network. Similar to the design steps above, the simplest model for a current-biased TMP61 linear thermistor network is the one shown in Figure 4-1 below. For the ADC, we will use 12-bit resolution and a reference voltage VBIAS of 5 V.

Figure 4-1 TMP6 Linear Thermistor Current Source Circuit

With an ADC reference voltage of 5 V, using a 200-µA current source to bias the TMP61 thermistor is a good option. The resulting Vtemp voltage swing from -40°C to 125°C is 1.3226 V to 3.58 V as shown in the simulation below.

GUID-20220106-SS0I-QXXF-8KVH-KFXWTWFDZD5T-low.pngFigure 4-2 TMP61 Thermistor Voltage Swing With 200-µA Current Source.

Varying the current when implemented with the TMP61 thermistor will increase the dynamic range of the output response. When biasing the TMP61 thermistor with currents between 50 µA and 400 µA, the output responses can be shown below:

GUID-195E979D-D0EA-4693-8A24-7D8D1724070A-low.gifFigure 4-3 TMP61 Thermistor Temperature Voltage With Varying Current Sources.

The proper value of the bias current is dependent on the reference voltage of the ADC in your system. You will want to choose the value so that the dynamic range is optimized with the full-scale range of the ADC input. In most cases, 200 µA is recommended. For lower system current draw a TI TMP6 linear thermistor of a higher nominal resistance such as the TMP64 (47 kΩ) and TMP63 (100 kΩ) thermistors can be used. The best current source implementation for the TMP64 (47 kΩ) and TMP63 (100 kΩ) thermistors are 42.533 µA and 20 µA, respectively.