TMP6131DECT datasheet(13/29 Pages) TI1

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Temperature (qC)

-60

-40

-20

100 120 140 160

d013

IBIAS = 50 PA

IBIAS = 100 PA

IBIAS = 200 PA

IBIAS = 300 PA

IBIAS = 400 PA

TMP61

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SBOS921 – DECEMBER 2018

Product Folder Links: TMP61

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Typical Application (continued)

A polynomial equation or a LUT can be used to extract the temperature reading based on the ADC code read in

the microcontroller.

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

output voltage of the divider circuit cannot be increased very much. Therefore, not all of the ADC codes will be

used 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, like the one shown in Figure 13, can be used to get 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 400 µA is used with the TMP61, the output voltage will span approximately

5.5 V and will have a gain up to 40 mV/C. Having control over the voltage range and sensitivity allows for full

utilization of the ADC codes and full-scale range. Based on the bias current, the temperature voltage is shown in

Figure 14. Similar to the ratio-metric approach above, if the ADC has built-in current source that share the same

bias as the reference voltage of the ADC, the tolerance of the supply current will be cancelled. In this case, a

precision ADC is not required. This method yields the best accuracy, but can increase the system

implementation cost.

Figure 13. TMP61 Biasing Circuit With Current Source

Figure 14. TMP61 Temperature Voltage With Varying Current Sources

In comparison to the non-linear NTC thermistor in a voltage divider, the TMP61 has an enhanced linear output

characteristic. The two voltage divider circuits with and without a linearization parallel resistor, RP, is shown in

Figure 15. For example, consider an example where VBIAS = 5 V, RBIAS = 10 kΩ, and a parallel resistor (RP) is

used with the NTC thermistor (RNTC) to linearize the output voltage with an additional 10-kΩ resistor. The output

characteristics of the voltage dividers are shown in Figure 16. The TMP61 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.

TMP6131DECT 数据表(PDF) 13 Page - Texas Instruments

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