Precision

Current Source

13

TMP63

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SNIS211C – OCTOBER 2019 – REVISED JUNE 2020

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Typical Application (continued)

Use a polynomial equation or a LUT to extract the temperature reading based on the ADC code read in the

microcontroller. Use the Thermistor Design Tool to translate the TMP63 resistance to temperature.

output voltage of the divider circuit cannot increase much. Therefore, this application design does not use all of

the ADC codes due to the small voltage output range compared to the FSR. This application is very common,

however, and is simple to implement.

A current source-based circuit, such as the one shown in Figure 16, offers better control over the sensitivity of

the output voltage and achieve higher accuracy. In this case, the output voltage is simply V = I × R. For example,

if a current source of 40 µA is used with the device, the output voltage spans approximately 5.5 V and has a gain

up to 40 mV/°C. Having control over the voltage range and sensitivity allows for full use of the ADC codes and

full-scale range. Figure 21 shows the temperature voltage for various bias current conditions. Similar to the

ratiometric approach, if the ADC has a built-in current source that shares the same bias as the reference voltage

of the ADC, the tolerance of the supply current cancels out. In this case, a precision ADC is not required. This

method yields the best accuracy, but can increase the system implementation cost.

Figure 16. Biasing Circuit With Current Source

In comparison to the non-linear NTC thermistor in a voltage divider, the TMP63 has an enhanced linear output

linear curve across the entire temperature range while the NTC curve is only linear across a small temperature

more linear but greatly affects the output voltage range.