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TMP63

SNIS211C – OCTOBER 2019 – REVISED JUNE 2020

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Typical Application (continued)

9.2.1.2.1

Thermal Protection With Comparator

Use the TMP63 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

9.2.1.2.2

Thermal Foldback

One application that uses the output voltage of the TMP63 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. 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 example). The device uses a buffer between the voltage