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DP83869HM: PHY to PHY capacitive coupling

Marco Ritter
Prodigy 70 points
Part Number: DP83869HM

Hi,

we have to use the DP83869HM as an media converter from MDI to SFP. The MDI Interface come from an I210 Ethernet controller.

So here is my question: Can i go through a capacitve coupling connection from PHY to PHY or should I use a magnetic coupling to connect the PHYs.

We won`t have long wires between the PHYs, because all components are on the same PCB.

 
  • 0
    TI__Mastermind 18425 points
    Hi Marco,

    Would you be using gigabit speed on the MDI? In that case the recommended solution is to use magnetics. We have tried some register settings that have shown good results for capacitive coupling at 1G speed but this is not a fully characterized solution.

    -Regards
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Prodigy 70 points
    Hi,

    thanks for the reply.

    At this moment I can‘t really say which speed we will use. This will be defined after a few tests with the three speeds.

    So how should the capacitive coupling look like? Are there differnents between 1000 or 100 megabit speed for the coupling. And can you give me a short overview with which register settings you had the best results?
  • 0 in reply to Marco Ritter
    TI__Mastermind 18425 points
    Hi Marco,

    For capacitive coupling, there should be 1 capacitor on each MDI trace between DP83869HM and Link partner. However, the link partner also need to support capacitive coupling. This is why I said it would be safer to use atleast one magnetics in between. DP83869HM has not be tested with other link partner for capacitive coupling since this not a IEEE standard method of isolation for Ethernet PHYs.

    For 100Mbps, you will only need 4 pins on the MDI channel. However, in that case 1Gbps will need to be disabled via register 0x09.

    -Regards
    Aniruddha