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LM3409 clarification on operation when led string is shorted

Jeff Coletti
Expert 8755 points

a load similar to Hi Support Team

Trying to understand what happens when the LED string is shorted? We are driving 2A into a string for 10 3v LEDs. Vin is 36 volts.

Will the regulator just drive the 2A into the short thus putting the power in the  FET, or will the Coff pin since the resistor is pulled to ground keep the device in an off state?

Thanks

Jeff

  • 0
    TI__Mastermind 25500 points
    In the datasheet it shows how to OR in another voltage for the off timer. The point is to keep the device switching and regulate the inductor/output current while the FET is on. This is how you get such fast edges during PWM dimming with a shunt FET. So yes, the current will be regulated through the FET and it will burn some power across its Rds(on). Out of curiosity is there any information you can share about this design such as the end product, input voltage range, and PWM dimming frequency/range requirements? I understand if not, but I like to know how people use our devices. Thanks.