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LM3478: unstable PWM and audible noise

Oleg Migal
Prodigy 10 points
Part Number: LM3478


Hello,

I want to use LM3478 as a simple led driver, schematic is attached. The problem is that I can't get a stable duty cycle on the DR output. Components mostly follow the WEBENCH POWER DESIGNER. What went wrong?

  • 0
    TI__Mastermind 23590 points

    Hi Oleg,

    I think this problem is related to the control loop.

    Have you tried with voltage loop only?

    Best Regards,

    Feng Ji

  • 0 in reply to Feng Ji
    Prodigy 10 points

    Thanks for the quick response!

    Yes, I have tried this solution and it really helps. But I want to achieve performance in its original form. I assumed that the inductance is too high for these conditions. In accordance with 8.2.1.2.2 Power Inductor Selection L>7.4 µH. Perhaps the inductor current ripple is not enough for correct operation. Since I have a limited range of inductance values, I increased the frequency to 470 MHz and applied a 4.7 uH. Now PWM is stable. I think my problem is solved.