TMP6331DECT datasheet(12/28 Pages) TI1

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TMP63

BIAS

TMP63

BIAS

TMP63

ADC Code

¸ u

TEMP

ADC Code

FSR

TMP63

TEMP

BIAS

TMP63

u ¨

Bias

TMP63

Filter

REF

GND

ADC

TMP63

SNIS211C – OCTOBER 2019 – REVISED JUNE 2020

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Typical Application (continued)

(yielding the highest accuracy and voltage gain). It is common to use a voltage divider with thermistors because

of its simple implementation and lower cost. The TMP63 has a linear positive temperature coefficient (PTC) of

resistance such that the voltage measured across it increases linearly with temperature. As such, the need for a

linearization circuits is no longer a requirement, and a simple current source or a voltage divider circuit can be

used to generate the temperature voltage.

This output voltage can be interpreted using a comparator against a voltage reference to trigger a temperature

trip point that is either tied directly to an ADC to monitor temperature across a wider range or used as feedback

input for an active feedback control circuit.

The voltage across the device, as described in Equation 2, can be translated to temperature using either a

lookup table method (LUT) or a fitting polynomial, V(T). The Thermistor Design Tool must be used to translate

Vtemp to Temperature. The temperature voltage must first be digitized using an ADC. The necessary resolution

of this ADC is dependent on the biasing method used. Additionally, for best accuracy, tie the bias voltage (VBIAS)

to the reference voltage of the ADC to create a measurement where the difference in tolerance between the bias

voltage and the reference voltage cancels out. The application can also include a low-pass filter to reject system

level noise. In this case, place the filter as close to the ADC input as possible.

9.2.1.2 Detailed Design Procedure

The resistive circuit divider method produces an output voltage (VTEMP) scaled according to the bias voltage

(VBIAS). When VBIAS is also used as the reference voltage of the ADC, any fluctuations or tolerance error due to

the voltage supply are canceled and do not affect the temperature accuracy (as shown in Figure 15). Equation 2

describes the output voltage (VTEMP) based on the variable resistance of the TMP63 (RTMP63) and bias resistor

(RBIAS). The ADC code that corresponds to that output voltage, ADC full-scale range, and ADC resolution is

given in Equation 3.

Figure 15. Voltage Divider With an ADC

(2)

where

•

FSR is the full-scale range of the ADC, which is the voltage at REF to GND (VREF)

•

n is the resolution of the ADC

(3)

Equation 4 shows whenever VREF = VBIAS, VBIAS cancels out.

(4)

TMP6331DECT Datasheet(PDF) 12 Page - Texas Instruments

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