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BQ25895: Failing EMC compliance

Nicolas Venturo
Intellectual 810 points
Part Number: BQ25895
Other Parts Discussed in Thread: PMP4451

Hello,

We're finishing a design based on the BQ25895, with QuickCharge inputs (12V 1.5A). We're not using the PMID output of the BQ25895. However, after doing EMC testing we noticed we're over the maximum allowed limit for the FCC certification, specially around 150 to 250 MHz.

We've based the layout design on TI's PMP4451 reference design, and tried to follow all standard EMI recommendations. Are there any tips in particular that apply to this IC? We're very late in the development process and need to find a solution very quickly. Attached you can find the test results for reference.

Many thanks

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    TI__Guru**** 165886 points

    4186.bq2589xbq2419x_29xlayoutandEMIrecommendation.pdfHi Nicolas,

    Attached is a presentation explaining how to minimize EMC.  In short,

    1.  Place PMID capacitors as close as possible between IC PMID and GND pins, even if that means pushing the inductor slightly farther away.

    2.  Add a high frequency decoupling cap (0.01-0.1uF) as the closest PMID cap

    3.  Minimize the size of the SW node

    4.  Place the SYS capacitors as close as possible

    5.  As a last resort, you can add a appropriately sized RC snubber from SW to GND at the expense of efficiency