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DP83848I: Trace Length

Part Number: DP83848I
Other Parts Discussed in Thread: DP83849I

Hello,

        Below is customer topology. Has any risk for signal integrity for it? 

        Do we also have Full duplex reference design and BMC to PHY to PHY to end device reference design to customer? Thank you.

BR

Patrick 

  • Hi Patrick,

    RMII trace lengths should be kept below 6000 mils. Trace 3, trace 4, trace 6 are very long for an RMII application. Yes, I would be concerned about signal integrity. Can the RMII traces be shortened at all?

    From your configuration, I do not believe we have a reference design.

    Best Regards,
  • Rob,

        May I learn what major concern on RMII length over 6 inches? timing lost, noise impact, ...

     

  • Hello Alan,

    The signal to noise ratio is impacted which might cause data loss or corruption. Long trace lengths are also a concern from an EMI point of view.

    I would like to ask one more question, are magnetics being used when connecting MDI of one PHY to MDI of another?

    -Regards,
    Aniruddha
  • Hi,

    I have same situation where the MDI differential trace is long (19 inches) and crossing PCB board boundary. My Ethernet link is not coming up.

    The RMII is synchronous interface do not meant to be long trace. In system design you don't want to run long trace for synchronous interface neither crossing PCB boards. If you do, I have seen backplane designs by converting synchronous interface to high speed differential traces, run for long distance and crossing PCB boards, and converting again back to synchronous interface. But design carefully for timing.

    My question: Do you see problem with the MDI differential traces for being long (19 to 21 inches) or even longer? I am using DP83849I device (dual Etherent port).

    Regarding the Ethernet magnetic, the MDI differential traces runs a long distance (total 19 ro 21 inches) from DP83849I (on PCB A), through PCB B, and reaching PCB C where the Ethernet magnetic is on PCB C.

    Thanks!

    David

    My email: dwong@claruspon.com