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Switching frequency on the PMP5725 reference design.

Richard Meyer
Prodigy 10 points
Other Parts Discussed in Thread: PMP5725

I’m looking at the feedback section of the datasheet regarding the filter setting.  The datasheet says to set the filter frequency to a decade above the max switching frequency.  I compared that statement to the PMP5725 reference design.  The reference design sets the filter to 80 kHz, yet the max switching frequency of the converter is 133kHz at full power.

I was thinking based on the datasheet information the filter should be set to 10*133kHz or 1.33MHz.  The PMP5725 would suggest that corner frequency of the filter is 8 kHz?  I’m confused.

  • 0
    TI__Expert 4015 points
    Hi Richard, I would say that the datasheet says to set the pole at 10*fsw to ensure that it doesn't impact on the control loop response. You can see in the PMP5725 schematic that the dominant pole of the feedback loop is set by C22 and R41 at ~340Hz. Since the pole at the FB pin is at ~80kHz, over two orders of magnitude away, it should have no impact on the loop in the crossover teritory. I would say in general that if you are doing a design I would follow the recomendation on the datasheet.

    Hope this helps.
    Thanks
    Billy