Micrel, Inc.

MIC2299

October 2007

13

M9999-101907-B

LED Protection

The operation of the Power LED must be limited to short

pulses to prevent overheating. This is usually controlled

by the micro controller in a typical application. For further

fail-safe protection, or where a micro controller is not

used, the temperature of the LED can be limited by the

addition of an NTC thermistor. The value should be

>100k

Ω at its maximum safe operating temperature.

This will then limit current drive to the LED as

temperature rises further and prevents overheating. This

thermistor should be connected directly from BRT to

GND. Reference Figure 10.

Figure 10. LED Thermal Protection