LM3401 high frequency dimming?

Lasse Lund Hansen

Other Parts Discussed in Thread: LM3401, LM3409

When you are designing a PWM LED driver it is best to have PWM frequencies above the hearing frequency range around 20kHz. This is due to the piezo acoustic properties of ceramic capacitors. They act as loudspeakers.

Has anyone experience with 20kHz dimming for the LM3401 controller?

The datasheet states a method of an external FET switch across the LED string.

Best regards

Lasse Lund Hansen

over 8 years ago

0 Lasse Lund Hansen over 8 years ago

Prodigy 50 points

Anybody out there?

0 Clinton Jensen over 8 years ago in reply to Lasse Lund Hansen

TI__Mastermind 25500 points

I haven't tried it on the bench, but it is a constant current buck converter, which means output current is continuous. You will need to switch the converter at a pretty high switching frequency for decent resolution, but you should be able to shunt FET dim at 20kHz. I believe the LM3409 has been tested at 20kHz+ shunt FET dimming as well.

0 Lasse Lund Hansen over 8 years ago in reply to Clinton Jensen

Prodigy 50 points

Thanks a lot. I will try out the solution in a mock up using PMN25EN from NXP as the shunting FET. it has a drain source resistance of 20mOhm

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LM3401 high frequency dimming?