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TMP63

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SNIS211A – OCTOBER 2019 – REVISED DECEMBER 2019

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Typical Application (continued)

8.2.1.2.1

Thermal Protection With Comparator

The engineer can use the TMP63, a voltage reference, and a comparator to program the thermal protection. As

shown in Figure 15, the output of the comparator will remain 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 15. Temperature Switch Using TMP63 Voltage Divider and a Comparator

8.2.1.2.2

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 TMP63 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 current is held at a

specified level until a high temperature is reached, known as the knee point, where the current must be rapidly

reduced. To better control the temperature/voltage sensitivity of the TMP63, a rail-to-rail operational amplifier is

used. In the example shown in Figure 16, the temperature “knee” where the foldback begins is 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 (like 110°C, for example). A buffer is used in-between the voltage divider with