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WEBENCH® Tools/LM3481: LM3481 Output ripple issue

Sahil Nayak
Intellectual 450 points
Part Number: LM3481

Tool/software: WEBENCH® Design Tools

Hello TI Team,

We are using LM3481 SEPIC converter with input voltage 9-36V and output voltage 12V @ 1.5A.

We are using this 12V only for LCD Backlight supply. Whenever we connect LCD, we are getting ripples of around 450mVpp @ switching frequency. Attached is the snapshot of waveform of ripples on the output rail in sync with its switching frequency and snapshot of schematic.

CH 2 - LM3481 switching waveform

CH3 - Output ripples.

Please suggest solution to reduce these ripples.

We have tried following solutions:

- Replaced C332 with 33pF and 100pF.

- Placed one more 47uF cap.

  • 0
    TI__Expert 7450 points

    Hi Sahil,

    Thanks for using LM3481.

    To me, your output switching ripple is OK (<40mV). Are you worried about those spikes?

    Those should be just the switching noise. Try probing the output voltage directly at the two terminals of the output cap using a short probe like tip and barrel.

    Please let me know if you have further questions.

    Thanks,
    Yinsong