AL5817

Document number: DS40391 Rev. 3 - 2

10 of 13

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August 2018

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AL5817

LED Thermal Compensation

The LED current is set by the reference voltage at the emitter/drain voltage of the LED driving transistor. This reference voltage is determined by

the resistor divider between REF and VSET. The LE

D driver’s LED current behavior under different ambient or LED temperatures can be

configured by using NTC for R6 shown in Figure 6.

Figure 6

In the example shown in Figure 7, the resistor network is comprised of one NTC and a resistor. When the temperature of the detecting point is

rising, the NTC resistance will decrease and make the voltage at VSET decrease also, consequentially, the output current will decrease to prevent

the system from over-heated.

Figure 7. Thermal Fold-back Circuit Basing on NTC

Thermal Protection

The AL5817 has an internal Over Temperature Protection (OTP). When the junction temperature is over +160°C, the IC will shut down. When the

junction temperature drops by +30°C the IC turn back on.