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Couple questions about PMP4447

Serdar Köse
Genius 3360 points

I have 2 questions regarding PMP4447.

1) The layout has a wire connection (or component?) named as CM1 but the schematic nor BOM list includes it. What is the purpose of it?What would be wrong if I just use copper path connection instead of CM1

2) C10 cap is defined as "470pF, Y CAP TH type" Is it recommended to use disk capacitor or can I use MLCC cap? Is C10 added after the design is done? I wonder if there is a good reason to mount the capacitor as it is shown on the above photo?

  • 0
    TI__Mastermind 34465 points
    CM1 is the location provided for a common mode EMI choke. If you check out the test data, it appears that the design passes conducted EMI emissions limits without the use of a common mode EMI choke. Therefore CM1 is not needed.

    C10 is part of the EMI filter and is used to attenuate the noise emissions. It is almost always a disc type capacitor and it has a high voltage safety rating since it couples the high voltage AC side with the low voltage, user accessible secondary.
  • 0
    TI__Mastermind 34465 points
    CM1 is the location provide for a common mode EMI choke. If you look at the test data for this reference design, it appears that the design passes EMI limits without the need of a common mode choke and therefore CM1 is not fitted.

    C10 is a "Y type" capacitor that is also part of the EMI noise reduction filter. It is almost always a disc type capacitor and it needs to have a safety agency rating. It isolates the high voltage primary side from the low voltage, user accessible secondary.
    It appears that the requirement for C10 was only discovered during EMI testing. That is why it is soldered onto the pcb in its present location.
    Normally its location does not matter too much but the pcb should be updated so that C10 is mounted like the rest of the through hole components.
  • 0 in reply to John Griffin1
    Genius 3360 points
    Hi again John,

    Is it possible to learn what EMI filter was used on CM1 just to have a reference?