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DP83867CR: Connect DP83867 with another PHY directly.

Chris Zhao1
Expert 1240 points
Part Number: DP83867CR

Hi experts,

I have a design using DP83867CRRGZ, while I have to connect it with another PHY directly, meanwhile the area in my board is very limited, so I have to use AC coupling mode to connect them together.

For DP83867CRRGZ, when I connected it with transformer, the center tap pin will be connect with GND by a 0.1uF, as for the other PHY, when connected with transformer, its center tap must be 2.5V, meanwhile it's 100M Ethernet, so I only use two pairs of signals.

What's the key for connecting two PHY connected, is it the common voltage? as the signal will be compatible with IEEE spec, is that right?

Back to TI PHY signals, current there is no pull-up/down for them, can this be feasible? Is there anything I missed?

 

Thanks

Chris

  • 0
    TI__Genius 11725 points

    Hi Chris,

    Can you provide a more complete schematic? For best performance with the DP83867, we recommend not using AC coupling. The differential pairs do not need pull-ups. 

    Thank you,

    Nikhil

  • 0 in reply to Nikhil Menon
    Expert 1240 points

    Hi Nikhil,

    Please refer to below for a more complete schematic, I have been using DP83867 in a bunch of projects, so I think the schematic design should be fine. The main reason I wanted to use AC coupling is the limited area available in my board, meanwhile I'm also using 100M Ethernet.

    I also made rework to one of my current board, and measured rx waveform in DP83867 RX side, which should be port B. I think it should be fine, I also verified that the "Ping" and "DHCP" can work. I want to get more professional input from TI, in case I miss something. 

    Thanks

    Chris

  • 0 in reply to Chris Zhao1
    TI__Genius 11725 points

    Hi Chris,

    This is a unique application and we have not tested this in regards to the IEEE spec compliance. You are correct, there should be no pull ups on the DP83867 signals. As far as requirements for connecting the other PHY, is this other device a TI PHY? If so, the datasheet will explain implementation of back-to-back mode. If the other PHY is not a TI device, please contact the manufacturer for requirements of back-to-back configuration. 

    Thank you,

    Nikhil  

  • 0 in reply to Nikhil Menon
    Expert 1240 points

    Hi Nikhil,

    Thanks, the other device is a switch from another vendor, that vendor also asked me why I didn't use their PHY.

    Even for DP83867 datasheet, I couldn't find the electrical info for PHY ports, so it should be just be compliant with IEEE spec, that's why I couldn't find it in datasheet, is that right?

    Anyway I'll have to move forward with current solution.

    Regards

    Chris