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LM3481-Q1: EMC

Hope Chen
Expert 1030 points
Part Number: LM3481-Q1
Other Parts Discussed in Thread: LM3481

HI,

  We use the LM3481 solution to design the SEPIC, but there have some EMC issue when we test EMC-class4,about over 2dB in 80 and 85Mhz

  input:6-9V

  output:7-7.5V/1A

Would you please help check SCH,and give us any advice to resolve the issue

Thank a lot

L-A# Mode1 CE Voltage 0.15-108MHz P+ 39欧+22欧磁珠.pdf

  • 0
    TI__Mastermind 21720 points
    Hi Hope,

    Thanks for reaching out with your question.

    The frequency range you are failing in is related to high frequency ringing. This can come from the switch nodes or from the diodes. Please probe the switch node (Drain of Q1, and anode of D6) to see if there is ringing in this frequency range. As snubber or extra ceramic capacitors can be used to help dampen out this frequency. Assuming the ceramic capacitors the are 0603 surface mount devices I would suggest adding capacitors in the 1nF to 10nF.

    If this doesn't help I can suggest a few other tactics.

    Thanks,

    Garrett