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Original question:

BQ25895: Failing EMC compliance

BQ25895: EMI EMC

Audi Chen
Prodigy 150 points
Part Number: BQ25895

Hi,

We're finishing a design based on the BQ25895, with QuickCharge inputs (12V 1.5A). However, after doing EMC testing we noticed we're over the maximum allowed limit for the FCC certification, specially around 150 to 250 MHz.

  • 0
    TI__Guru 56411 points

    Hi,

    The EMI could be sourcing from:
    1.Cables with length 0.3 to 0.7m range radiation in the range
    2. Damped SW ringing, either from the ringing or the falling edge.

    The following actions may be helpful:
    1.Add 1nF PMID, SYS, VBUS (opt.), BAT (opt.)
    Recommend X7R 1nF (0402) which typically has > 300M resonant frequency. Please check with vendor for impedance response.
    The cap on PMID with minimal loop with IC is the top priority.
    2.Slower SW node switching slew rate
    Resistor footprint at BTST to adjust slew rate if needed.
    Higher resistor value (slower slew rate) can adversely affect converter efficiency.
    3.Use Snubber to reduce EMI
    Snubber (resistor & capacitor) footprint at SW to control EMI source
    Components must be placed closest to SW to be effective
    4.Use EMI bead to reduce EMI
    EMI Bead footprint at VBUS and PMID to suppress EMI
    EMI beads selected must be able to handle high power with high impedance between 100MHz and 250MHz to effectively filter EMI at required FCC frequency range.
    5.The load connection is also very important. An external wider and shorter wire may improve EMI performance.

    Thanks,

    Ning.