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BQ25731: EMI related questions

Nicholas Carley
Genius 9925 points
Part Number: BQ25731

On the reference design for the BQ25731, the LoDrv MFETs have 150pF caps across their gates;  150pF seems rather high - is this critical to slow down the gates for radiated emissions compliance? - or other reason?   

Several TI applications notes for reducing EMI suggest a series resistor between the HiDrv gate driver bootstrap input pin and bootstrap capacitor;  would this work well also for the BQ25731? – as in resistors on C1 and C2 between the BTST1 and BTST2 pins respectively? 

  • +1
    TI__Genius 11385 points

    Hi Nicholas,

    Thanks for reaching out.

    Yes, you are correct. The 150pF caps are to slow down the turn-on and turn-off speed. It helps to reduce EMI. You can have a placeholder there but leave it unpopulated for prototype board/initial testing.

    There is no C1 or C2 on the schematic. However, if you are talking about C15, C16, yes you can add a series resister from there to BTST to slow the turn-on.

    In this area, you can treat the power stage design of our chargers the same as other DC-DC converters.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory