TMP64 datasheet(12/28 Pages) TI

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TMP64

BIAS

TMP64

BIAS

TMP64

ADC Code

¸ u

TEMP

ADC Code

FSR

TMP64

TEMP

BIAS

TMP64

u ¨

Bias

TMP64

Filter

REF

GND

ADC

TMP64

SNIS212B – DECEMBER 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 TMP64, on the other hand, 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 TMP64, 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, the bias voltage (VBIAS)

should be tied 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 engineer can also implement a low-pass

filter to reject system level noise, and the user should 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 is canceled and does not affect the temperature accuracy. This type of configuration is shown

in Figure 12. Equation 2 describes the output voltage (VTEMP) based on the variable resistance of the TMP64

(RTMP64) 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 12. TMP64 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)

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