TMP6331QDECTQ1 datasheet(13/26 Pages) TI

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TMP63

BIAS

TMP63

BIAS

TMP63

ADC Code

¸ u

(4)

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-Q1 resistance to temperature.

The cancellation of VBIAS is one benefit to using a voltage-divider (ratiometric approach), but the sensitivity of the

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 8-6, 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 8-11 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.

VTemp

RTMP63

IBias

Precision

Current Source

Figure 8-6. Biasing Circuit With Current Source

In comparison to the non-linear NTC thermistor in a voltage divider, the TMP63-Q1 has an enhanced linear

output characteristic. The two voltage divider circuits with and without a linearization parallel resistor, RP, are

shown in Figure 8-7. Consider an example where VBIAS = 5 V, RBIAS = 100 kΩ, and a parallel resistor (RP) is

used with the NTC thermistor (RNTC) to linearize the output voltage with an additional 100-kΩ resistor. The

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

small temperature region. When the parallel resistor (RP) is added to the NTC circuit, the added resistor makes

the curve much more linear but greatly affects the output voltage range.

RBias

VBias

VTemp

RTMP63

VTemp

RNTC

RBias

VBias

Figure 8-7. TMP63-Q1 vs. NTC With Linearization Resistor (RP) Voltage Divider Circuits

www.ti.com

TMP63-Q1

SNIS215C – JANUARY 2020 – REVISED SEPTEMBER 2020

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