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DP83867IR: DP83867IRRGZT Schematic Review for 100M/1G Ethernet with PoE and External Magnetics

Nikhil Soliya
Prodigy 30 points

Part Number: DP83867IR

Hello,

We are designing a product using the DP83867IRRGZT PHY and have configured it to support both 100 Mbps and 1 Gbps Ethernet operation.

I have attached the schematic of the PHY section.

20-XXXXX_Retrofit_Sphere-XAP_Rev1.0_20260605_Ethernet.pdf 

Could you please review it and let us know if there are any additional points or design considerations that we should take care of?

The system is powered through PoE, and I have also attached the schematic of the magnetics section along with the connector interface. The Ethernet signals are routed through a flat cable connector before reaching the RJ45 connector.

Could you please advise if any special care is required for this arrangement, especially considering Gigabit Ethernet operation? Also, please let us know if there are any recommendations regarding the PHY-to-magnetics connection, signal routing, PoE implementation, or PCB layout.

Thank you for your support.

  • 0
    TI__Mastermind 37565 points

    Hi Nikhil,

    1. I notice you flip signals between the magnetics and the RJ-45 here:

    When it comes time to design the layout, it would be preferrable to avoid this swapping of signals as it will add length and vias to each trace. DP83867 has a mirror mode that can be used to swap the lanes on the PHY so you would not need to flip the signals.

    2. The turns ratio tolerance on your magnetics is 3%, whereas our DP83867 datasheet recommends 2%. I strongly recommend using magnetics that meet or exceed the specs in this table of the PHY datasheet:

    3. Double check that your crystal meets the specs in the PHY datasheet as well.

    Otherwise the PHY implementation looks ok. I strongly recommend looking through our DP83867 schematic checklist as a second check on the design.

    If you are routing ethernet MDI signals through a flat cable between the magnetics and RJ-45, I would keep this cable as short as possible. For context we usually recommend using MDI traces with total length around 2 inches and all on the same board. A flat cable, while not ideal, may still work, though I would aim to keep the total MDI length near that 2 inch recommendation.

    Best,

    Shane