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DP83867IS: Questions on Output Impedance and Current Drive

Nicholas Mariani9
Intellectual 2100 points
Part Number: DP83867IS
Other Parts Discussed in Thread: HD3SS3212

Hey Team,

I am planning on using the DP83867IS in a media conversion application where I am trying different transmission mediums. I would like to use the PHY in a back to back config where:

MDI <--> PHY <--> SGMII <--> Media <--> SGMII <--> PHY <--> MDI

I have two transmission mediums I will switch between using the HD3SS3212 passive switch. The first will be going to a fiber transceiver (SFP) that is on board so I have no concerns about drive strength here. The second media will be SMA coax of 50ohm impedance; full channel link looks like the following:

PHY <--> SGMII <--> HD3SS3212 <--> co-ax/fiber <--> HD3SS3212 <--> SGMII <--> PHY

My concern is based on the output drive of the 100Ohm diff. impedance SGMII signal and how long I can have the co-ax. I would like to attach a 1m cable but the following E2E post suggests that I will only get 18 inches total including board trace:

https://e2e.ti.com/support/interface/ethernet/f/903/p/601979/2215669?tisearch=e2e-quicksearch&keymatch=sgmii%20impedance#2215669

Is there a way to tell what the output current drive is and if I will need to add a line driver to the signal chain? Additionally, could you take a quick look at the switch to verify that it will work for this application? I see no issues with it when I read through the datasheet but having a second pair of eyes could help. 

Bonus Question: Ideally instead of using SMA connectors I would like to use a Type-C cable for transmitting the 1GigE signal but USB is 90 Ohm diff. impedance. Do you have any tricks on an efficient way to run the signal over a Type-C cable? It would be very convenient so that I can run power to another board over the same cable as the test signals.

Best Regards,

Nick

  • 0
    TI__Intellectual 2100 points
    Hey Team,

    Can anyone with available bandwidth address this issue for a fellow TIer'?

    Best Regards,
    Nick
  • 0 in reply to Nicholas Mariani9
    TI__Mastermind 18425 points
    Hi Nick,

    This is a unique application so it would need to be looked into. The 18 inch limit was for microstrip traces on a FR-4 medium which has different loss characteristics compared to a co-ax. We have IBIS model for DP83867 SGMII which you can use to estimate if the medium you are using will be good enough or not. For your co-axial solution however, you have a Mux/Demux before connecting to the co-ax media. It looks like the co-ax cable reach will depend on the Mux/Demux and not the PHY. Please correct me if I am missing something here.

    Passing SGMII over 90ohm USB-C cable is also different than what is usually implemented. I would again point you to SGMII IBIS model for getting an idea through simulation. The sgmii ibis model is on www.ti.com/.../toolssoftware


    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    TI__Intellectual 2100 points
    Thanks Aniruddha,

    You are correct, simulation is probably my best friend here. The IBIS link should help out. To my knowledge, the mux/demux that I pointed out is passive and has no drive strength at all. Perhaps this is not accurate?

    Nick