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BQ24296M: RF noise issue.

Liubomyr Holovatskyi
Prodigy 10 points
Part Number: BQ24296M

Tool/software:

Hello.

Our products using BQ24296M have an issue with RF noise that significantly affects on our RF subsystem at 868/915MHz.
RF noise from BQ24296M starts when switching converter goes to continuous current mode.

It looks like synchonous switching converter does not work well.

Switcing process has a long dead time. LSFET Rds on is relatively high.

I suspect that this causes RF noise, typical for non-syncronous converters.
Design description is here e2e.ti.com/.../bq24296m-emi-issue-during-pmic-switching

The suggestions from this topic did reduce the noise by 3-5 dB, which is insufficient.

Could you please suggest how to reduce RF noise further?

  • 0
    TI__Mastermind 27325 points

    Hello, 

    Thank you for reaching out via E2E. 

    The 3 techniques listed to reduce EMI shared in the previous thread you linked remain TI's recommendation. Can you please help to share more details on what you specifically implemented to reduce noise by 3-5 dB. 

    Liubomyr Holovatskyi said:
    Could you please suggest how to reduce RF noise further?

    My only additional suggestion is to try adding an EMI bead at VBUS input to further suppress noise. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Intellectual 355 points

    Hi Garrett. Could you also comment on the issue regarding non-synchronous switching? Is it an expected behavior?

    BR, Vasyl.

  • 0 in reply to Vasyl Vorobei
    TI__Mastermind 27325 points

    Hi Vasyl, 

    The BQ24296M is a synchronous buck converter as it has an integrated LSFET (denoted Q3 in functional block diagram on datasheet page 15). 

    Dead time during switching is expected to ensure both switching FETs are not on at the same time therefore preventing shoot-through. 

    Below is a waveform of SW node on BQ24296MEVM board and as you can see the dead time is within reason the same as you observe. 

    Best Regards,

    Garrett