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LM3402: LM3402: large current ripple?

Shawn Lin
Prodigy 60 points
Part Number: LM3402

I was using LM3402 to drive one 1W high power LED of 530nm, set current sensing resistor as 0.56 Ohm. Input a PWM dimming signal of 80kHz. Found some wave strange as attached using current probe on scope.

That seems current wave performed as ripple with same 80kHz frequency. I don't know if it was expected. Look forward to any help. Thanks.

  • 0
    TI__Mastermind 25500 points

    Hello Shawn,

    That looks as I would expect. 80kHz is a very high dimming frequency so you are seeing the rising/falling edges of the inductor current. If you reduce the frequency you will see more switching cycles during the on time. But this is how the part PWM dims (slews to full current, starts switching normally, then the current falling when turned off, all governed by v=Ldi/dt).

    Regards,

    Clint