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Original question:

DP83825I: Transformer center tap connection

DP83869HM: center tap capacitor on the PHY side

Zehui Li
Intellectual 540 points
Part Number: DP83869HM

Tool/software:

Hi，

   Could you explain the reason why use center tap capacitor on the PHY side? I read many datasheets and design guides, none of them tells the reason and thet just say "it's a rule. Follow it."

  • 0
    TI__Mastermind 24998 points

    Hi Zehui,

    From my understanding, magnetics will filter out most of the energy during ESD strikes, but some remaining energy may still couple to the PHY. Capacitors on center taps are used to filter out the remaining noise from the ESD event. The calculation for this is not straight-forward due to variance in the parasitics of the CMC and layout design - we use 0.1uF as a rule of thumb.

    Thank you,

    Evan