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  1. #1
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    Noise coupling into DCDC module via the ground copper pour directly beneath it?

    Hi,
    Please assist in telling if noise could be coupling into our DCDC module via the ground plane that we have underneath the module? Maybe we should remove the ground plane under the Vicor DCM3623T50M53C2T00 DCDC module? We have connected pri and sec grounds and have that joint ground directly under the module.
    Maybe this is why Vicor have a separate, unconnected, EMI ground under the module in their example layout of page 87 of the DCM design guide?

    DCM design guide:
    http://www.vicorpower.com/documents/...uide-VICOR.pdf

    We know that the Brilliant Vicor DCM3623T50M53C2T00 DCDC modules are in used in millions of PSU’s so assumed that people must have the gerbers for the Demo Board on page 7 of the following document? If so please could you send them here?

    Vicor Eval Board:-
    http://www.vicorpower.com/documents/..._EvalBoard.pdf


    ………………*……………………*………………*……………………*………………*……………………*

    We are suspecting that since we are using it non isolated on our own test PCB, and just have a single common ground plane under the DCM module, this may be causing our noise issue. We suspect noise from the module is coupling into the ground pour directly under the module and getting back into the DCM3623 and interfering with it. Do you think this is possible? If we could see the gerbers of the Eval Board, then this would go some way to confirming this.

    I suspect that the Vicor Eval board has only chassis ground copper pour directly under the module, but would just like to confirm this with the gerbers?

    We noticed that the demo board schem on page 7 has a chassis ground connection, and that this is isolated from the circuit primary and secondary grounds. We also noticed that Y capacitors have been place from chassis ground to all the four power rails. However, we noticed that no common mode choke is used. Please could you advise if there is a reason that no common mode choke was used, since, as you know, it is usually needed to form the LC common mode filter with the Y caps?

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  2. #2
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    Re: Noise coupling into DCDC module via the ground copper pour directly beneath it?

    I would expect that the DC-DC inductor is the EMI aggressor,
    but DC-DCs also contain "victim" circuitry which means they
    can "self-harm" very easily (charge pumping Vref or FB pins,
    FET near-zero-current servo) which are ground referred).

    Seems like you know the right answer, why not whip out
    the Dremel and see what you get (probably more instructive
    than random Internet opinions)?


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  3. #3
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    Re: Noise coupling into DCDC module via the ground copper pour directly beneath it?

    The noise in the output current is solved by reducing the output capacitance to 220uF.
    -But the datasheet states that up to 2mF should be allowable at the output...so we are surprised we get noise in the output current when we use more than 220uF.

    Incidentally, the Eval board for this module only has 220uF on it.

    DCM3623T50M53C2TOO Eval board, page 7...
    http://www.vicorpower.com/documents/..._EvalBoard.pdf

    Attached shows vout yellow and iout in purple...(ACS722 current monitor output) (VIOUT - 0.33)/0.264 Amps
    ....with 680uF on output...and noise is seen



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