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TMP63-Q1

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SNIS215 – JANUARY 2020

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Typical Application (continued)

8.2.1.2.1

Thermal Protection With Comparator

Use the TMP63-Q1 device along with a voltage reference, and a comparator to program the thermal protection.

As shown in Figure 18, the output of the comparator remains low until the voltage of the thermistor divider, with

comparator signals an overtemperature warning signal. The engineer can also program the hysteresis to prevent

the output from continuously toggling around the temperature threshold when the output returns low. Either a

comparator with built-in hysteresis or feedback resistors may be used.

Figure 18. Temperature Switch Using Voltage Divider and a Comparator

8.2.1.2.2

Thermal Foldback

One application that uses the output voltage of the TMP63-Q1 in an active control circuit is thermal foldback.

This is performed to reduce, or fold back, the current driving a string of LEDs, for example. At high temperatures,

the LEDs begin to heat up due to environmental conditions and self heating. Thus, at a certain temperature

threshold based on the LED's safe operating area, the driving current must be reduced to cool down the LEDs

and prevent thermal runaway. The device voltage output increases with temperature when the output is in the

lower position of the voltage divider and can provide a response used to fold back the current. Typically, the

device holds the current at a specified level until a high temperature is reached, known as the knee point, at

which the current must be rapidly reduced in order to continue operation. To better control the

temperature/voltage sensitivity, the device uses a rail-to-rail operational amplifier. I Figure 19 shows the

temperature knee point where the foldback begins. The set by the reference voltage (2.5 V) at the positive input,

and the feedback resistors set the response of the foldback curve. The foldback knee point may be chosen

based on the output of the voltage divider and the corresponding temperature from Equation 5 (110°C, for