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UCC33420: EMC problems with UCC33420

Martin Wassermann
Prodigy 50 points
Part Number: UCC33420

Tool/software:

Good day,
I use the UCC33420 to supply an isolated current measuring amplifier. I have provisionally soldered it to the board with thin copper wires. I attached 2n2 and 10µF directly to the IC. In a preliminary EMC measurement I get massive interference at approx. 7.5MHz. I think the problems are due to my provisional assembly. However, I cannot understand why I get interference at 7.5MHz. The device works at 75MHz! Does the device work internally with a PLL?
Can I assume that the EMC results are OK if the device is mounted correctly?


  • 0
    TI__Genius 15566 points

    Hi Martin.

    -Firstly, the 7.5MHz should not come from UCC33420. I recommend checking the Noise Floor of your EMC test and also testing the isolated amplifier itself to discard those two potential noise sources of the 7.5MHz.

    -Secondly, please share Schematic and Layout of the DUT. Definitely, the provisional assembly is not recommended, this DC/DC isolated bias supply switches at 76MHz. The HF harmonics will resonate with the parasitic inductances of these wires. An appropriate layout and EMI filter is needed to achieve low EMI.

    -Finally, could you please share the specifications (VIN, Vout, Pout) and the Standards of your test (CISPR32, CIPSR25, CE/RE)? Depending on that I will recommend an EMI filter BOM and layout guidelines along with results. Please, send me your email to share that information. You can send me a private message.

    Thank you