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LM5175: dithering cap range

Ann_Lien
Genius 14430 points
Part Number: LM5175

Hi expert,

My customer wants to know how to determine FMOD value in dithering function. Do we have a suggest range in dithering cap? Thanks!

Best regards,

Ann Lien

  • 0
    TI__Guru* 78220 points
    Hi Ann,

    The dithering cap determines the frequency sweep speed. A smaller capacitor leads to faster sweep speed. The ideal case is that the frequency sweep completes once within the time window allowed by the EMI test setup's resolution bandwidth. However, the sweep speed should also be slower than the power converter's loop speed, otherwise the output voltage will show large ripples at the frequency of the frequency sweep.

    So, they need to know the resolution bandwidth, and the converter loop bandwidth, to select an appropriated capacitor at the the DITH pin.

    Thanks,
    Youhao
  • 0 in reply to Youhao Xi
    TI__Genius 14430 points

    Hi Youhao,

    Thanks for your feedback!! So we need to run frequency response to know system bandwidth and look into EMI test condition to see the resolution bandwidth to determine how fast FMOD is. After getting these data, all we need to do is to try which FMOD is good to cancel EMI, right? Or do we have any standard or formula to determine FMOD? Thanks a lot!!

    Best regards,

    Ann Lien