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DP83848 max capacitance

Will Jarrett
Expert 3415 points

Customer is considering the DP83848 part.  He wants to put ESD/lightning protection on the PHY side of the magnetics.  Can you help us to understand capacitance can be tolerated on the txd/rxd lines?

 

Thank you,

  • 0
    TI__Mastermind 31600 points
    Jarrett,

    Adding capacitance on the transmit and receive differential pairs can impact the PHY in a couple ways. From a system level perspective, they can reduce the cable reach (the length of cable over which the PHY can transmit and receive without error). From a compliance perspective, they can affect return loss and rise/fall times.

    Keeping the capacitive loading below 5pF would be recommended. Keeping the capacitive loading below 1-2pF would be preferred.

    Patrick