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

2.1 Voltage-Biased NTC Thermistor Network

The simplest construction of the NTC thermistor-based temperature sensing network is the one shown in Figure 2-1. For the ADC, we will use 12-bit resolution and a reference voltage of 5 VDC. The 12-bit resolution is an acceptable resolution for measurement while the 5 VDC reference voltage simplifies power rail requirements. These design decisions result in the voltage response shown in Figure 2-2.

Figure 2-1 Simple Voltage Biased NTC Thermistor Schematic.
GUID-58B976DC-07E1-46AA-9C8B-8DC3572A5191-low.pngFigure 2-2 NTC Thermistor Voltage Response (5 V).

While this voltage-biased network is very simple, reducing the bill of materials cost required. The temperature output VTEMP shows non-linear behavior at the temperature extremes.