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DP83867IR: max. distance between magnetics and PHY

Stani Bell Ngoufack Tchoufack89
Intellectual 2020 points

Part Number: DP83867IR

Hello,

my customer is currently doing a design with the DP83867IRRGZ and he has a question:

his new design places magnetics and PHY on two separate boards being connected with a high speed connector.

Do you know any constraints concerning the maximal distance between PHY and magnetic?

Perhaps you know any guidelines – besides the PHY-datasheet  (length matching, impedance, ...)

Regards,

Stani

 

  • 0
    TI__Expert 5670 points
    Hi Stani,

    Please go over AN-1469 PHYTER® Design & Layout Guide, especially section 2, under Technical documents of DP83867.

    Link www.ti.com/.../technicaldocuments

    Regards,

    Hung Nguyen
  • 0 in reply to Hung Nguyen92
    TI__Intellectual 2020 points

    Hi Hung Nguyen,

    thanks for your hints.

    What the customer couln't find but is highly interested in, is the length (matching) of the interface between PHY and RJ45 with integrated magnetics (see picture).

    The document sets up a length requirement only for the MII-interface betweenMAC-interface and PHY.

    For the distance between PHY and RJ45, only the following can be found:

    Have you got any ideas? (Max Length? matching pair <-> pair & n<->p ?)

  • 0 in reply to Stani Bell Ngoufack Tchoufack89
    TI__Expert 5670 points
    Hi Stani,

    1. For Max length: there is no max trace length recommendation on the MDI. Longer traces will result in higher loss and can impact cable reach and IEEE compliance test result. In general, the trace length from the PHY to the RJ-45 connector should be less than 3 inches. However, longer traces would also work depending on what is the acceptable cable reach for a system.

    2. For length matching, below is what specifies in the app note:
    - Within the pairs (for example, TD+ and TD-) the trace lengths should be run parallel to each other and matched in length. Matched lengths minimize delay differences, avoiding an increase in common mode noise and increased EMI.

    In addition, MDI trace lengths should be matched between all 4 pairs.

    In the same app note, there is discussion about crossing power/GND plane for MDI routing. You will need to take care of that for your application with mating connector on MDI lines.
    - Signal traces should not be run such that they cross a plane split. See Figure 4. A signal crossing a plane split may cause unpredictable return path currents and would likely impact signal quality as well, potentially creating EMI problems.

    Regards,

    Hung Nguyen