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omapl138 EMAC pcb layout

ben zhan
Intellectual 700 points
Other Parts Discussed in Thread: OMAPL138

hi,

     Here is a Problem: My Omapl138 EMAC controler to PHY is 100mm , PHY  to RJ45  120mm, TX+/TX-, RX+/RX- trace length 120mm,  Length distance may case singal quality bad,  but This is a shortest distance on my board.  Is there any suggestion.

Thanks!

  • 0
    TI__Intellectual 1670 points

    Generally it's not distance (on PCBs) that causes problems, it's an impedance mismatch or discontinuity.  I don't think these lengths are too long as long as you follow the rules on trace impedance.  If the trace impedances are constant over the length of the trace (not crossing over plane splits and stays the same width), and they don't run too close to noise sources, you should be fine.

     

    Differential coupling is not as important on a PCB as keeping a good single ended impedance, so try to meet the spec for the differential impedance, but definitely meet the spec for the single ended impedance, and keep the impedance constant over the length of the trace.

    If you can do that, you should be fine.