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PMP5593: Necessity of C19 in schematic

ibbidy2
Prodigy 60 points

Part Number: PMP5593

Hello,

     Thank you for the reference design.  I am not clear on the necessity for C19 (I believe this is a "CY" capacitor).  I have an application where the a similar design gets worse conducted emissions results when the output voltage is referenced to earth ground.  However, when the CY cap is removed the situation improves.

Thanks,

Ted

  • 0
    TI__Intellectual 810 points

    Hi Ted,

    The C19 capacitor is in fact acting as a "CY" capacitor. The purpose of a "CY" capacitor is to isolate the output and input returns path. The cap will minimize the common mode voltage noise that could potentially couple into your ground. If any of this noise is couple into your input return path it could result in worse conducted emissions. It will essentially act as a filter.

    -Raymundo Hernandez-Toscano