9 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification, and TI

does not warrant its accuracy or completeness. TI’s customers are responsible for determining

suitability of components for their purposes. Customers should validate and test their design

implementation to confirm system functionality.

9.1 Application Information

The TMP64 is a positive temperature coefficient (PTC) linear silicon thermistor. The device behaves like a

temperature-dependent resistor, and may be configured in a variety of ways to monitor temperature based on

the system-level requirements. The TMP64 has a nominal resistance at 25 °C (R25) of 47 kΩ , a maximum

operating voltage of 5.5 V (VSns), and maximum supply current of 100 µA (ISns). This device may be used in a

variety of applications to monitor temperature close to a heat source with the very small DEC package option

compatible with the typical 0402 (inch) footprint. Some of the factors that influence the total measurement error

include the ADC resolution (if applicable), the tolerance of the bias current or voltage, the tolerance of the bias

resistance in the case of a voltage divider configuration, and the location of the sensor with respect to the heat

source.

9.2 Typical Application

9.2.1 Thermistor Biasing Circuits

Figure 9-1. Biasing Circuit Implementations With Linear Thermistor (Left) vs. Non-Linear Thermistor

(Right)

9.2.1.1 Design Requirements

Existing thermistors, in general, have a non-linear temperature vs. resistance curve. To linearize the thermistor

response, the engineer can use a voltage linearization circuit with a voltage divider configuration, or a resistance

linearization circuit by adding another resistance in parallel with the thermistor, RP. Section 9.2.1 highlights the

two implementations where RT is the thermistor resistance. To generate an output voltage across the thermistor,

the engineer can use a voltage divider circuit with the thermistor placed at either the high side (close to supply)

or low side (close to ground), depending on the desired voltage response (negative or positive). Alternatively, the

thermistor can be biased directly using a precision current source (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

TMP64

SNIS212C – DECEMBER 2019 – REVISED SEPTEMBER 2020

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