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BQ25886: Question about ferrite bead with capacitor on D+ and D- (for EMI test)

Satoshi
Guru 19645 points
Part Number: BQ25886

One customer is evaluating bq25886, but D+ and D- are failed EMI testing.

・Ferrite bead ⇒ serial 10Ω ⇒ D+ or D- pin : Test failed 

・Ferrite bead ⇒ 2700pF to GND ⇒ serial 10Ω ⇒ D+ or D- pin : Test OK 

　※10Ω is necessary to set by customer's condition

Please let me confirm about problem or not for additional capacitor after the ferrite bead on D+ and D- line.

If no problem, I found below thread described on "0.01-1uF at input before or after the ferrite bead".

Is 2700pF capacitor value OK?

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/876637/bq25886-fcc-certification-issues

Best regards,

Satoshi

  • 0
    TI__Genius 11850 points

    Hi Satoshi,

     

    I don't see a problem with adding the 2700 pF cap to GND.

     

    Is the EMI performance significantly worse if you remove the ferrite beads for D+/D-? Typically, ferrite beads are placed on the input and output power pins (such as VBUS, VSYS, and VBAT) to help filter out high-frequency noise.

     

    Best regards,

    Angelo