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Original question:

BQ24250: Problem with SYSOFF functionality

BQ24250: Problem with radiation emission

NIkola Suljagic
Prodigy 140 points
Part Number: BQ24250

Hi to all, 

I decided for bq24250 battery charger to use in my application. When the USB type C connected with battery charger (the battery is charging process), there is not Allowed Radiation at certain frequencies. When I disconnect USB, the radiation is significantly lower. I did measurement of spectrum and radiation is bigger then allowed when battery charger connected with USB type C and charging in process. I measured environment spectrum and spectrum in power supply network. There are reports of these measurement in attachment. Also you can see battery logic schematics in attachment. Can someone help me find the problem? And how can I resolve this? 

Also, would someone recommend me to some other charger which doesn't have this problem? 

Best regards and thanks in advance,

Nikola

This is the spectrum of power supply spectrum in charging process:

 

This is the spectrum of environment in charging process:

  • 0
    TI__Guru 56650 points

    Nikola,

    We didn't do much board level EMI research and tests. I can just give common suggestion. 

    1. Please measure the SW node to check the switching node ringing and compare the ringing frequency to the spectrum result. If that frequency noise is too high, you may think about adding a snubber on switching node or putting a series resistor on BOOT capacitor to slow down the switching node rising edge.

    2. If the test point is a components, please remove it.

    3. How many layers is your board? Please add ground layer to shield the internal noise if possible

    4. Add 0.1uF 0402 capacitor on board terminal.

    5. Move C31 and C26 close to IC.

    6. Add 0402 capacitor paralleling with C31 and C26 and put them between the C31/C26 capacitor and the IC.

  • 0 in reply to Wang5577
    Prodigy 140 points

    Hi Wang, 

    Thank you very much for your prompt reply, I'll try your suggestions. Can you tell me if I would solve my problem with a linear charger instead of charger with switch mode? 

    Best regards, 

    Nikola

  • 0 in reply to NIkola Suljagic
    TI__Guru 56650 points
    Nikola,

    I would think the linear charger doesn't have this radiation emission problem.
  • 0 in reply to Wang5577
    Prodigy 140 points
    Wang,
    Thank you for all recommendations, If I do not manage to solve the problem with an existing charger, I will try with some linear charger.
    Best regards,
    Nikola
  • 0 in reply to NIkola Suljagic
    TI__Guru 56650 points
    Nikola,

    Thanks, please let me know your experience with the existing charger. We may learn something from it.