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BQ24770: Asking for advise to reduce EMI

Jay Yoo
Intellectual 2061 points
Part Number: BQ24770

Hi expert,

My customer is designing BQ24770 and they are facing EMI problem. Currently they are using 800kHz of Fsw and the EMI result is bad at 73.3M or 73.4MHz. 

In this case, Can you review my below questions?

Q1. What would you suggest for the switching frequency at 3.3uH inductor? Is it better to lower or to higher?

Q2. Is it okay to add a snubber at the SW node(before inductor) for BQ24770?

If there's any better idea to reduce EMI, please let me know.

  • 4cells(16.8V)
  • minimum system voltage: 16.8V
  • Adapter voltage: 19V

Thnaks,

Jay

  • 0
    TI__Genius 16740 points

    Hello Jay,

    Jay Yoo said:
    Q1. What would you suggest for the switching frequency at 3.3uH inductor? Is it better to lower or to higher?

    I would recommend between 600kHz and 800kHz for the switching frequency if your using a 3.3uH inductor. 

    Jay Yoo said:
    Q2. Is it okay to add a snubber at the SW node(before inductor) for BQ24770?

    Yes, it is okay to add a snubber at the SW node.

    Jay Yoo said:
    If there's any better idea to reduce EMI, please let me know

    Adding a snubber at the SW node should reduce some of the EMI, another option is to add a Pi filter across the inductor to reduce the EMI. Texas Instruments also has many documents online regarding ways to reduce EMI.

    Regards, 

    Christian