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LM3414HV output breakdown?

Rene Jansen
Prodigy 70 points
Other Parts Discussed in Thread: LM3414HV

Hello

On our board we have placed 8 LM3414HV LED drivers to drive 8 different LED strings. Of these LED strings only 1 LED string is active at a certain time.

First time when power is supplied, everything goes fine. The second time when power is supplied a single LED string is active with a very small current (but more than the leakage current, several mA). No switching at the driver output is obserbved, but the chip is getting hot. It seems like the driver FET is in lineair mode. But turning the LED string on at full power (by setting the DIM pin) still works. Eventuelly the driver gets overheated and the DIM pin won't work any more. But the LED string is still getting the small current.

We also have noticed that the internal Vcc voltage regulator (that we used to provide power to the input stage) is not stable, despite a 1uF capacitor. we have disconected the VCC supply from the input circuits using a sepearte power supply for them, but that didn't work.

Can this be caused by the absence of a input capacitor?

  • 0
    TI__Mastermind 25500 points
    Buck regulators have discontinuous switching input current and absolutely require an input capacitor or they will be damaged. Each of the 8 should have its own input capacitor placed close to the input pin of the IC. The input capacitor ground should also be close to the IC ground and the current sense resistor ground.