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33 ohm terminators recommended in SLVA531A paragraph 4.3

Robert Curtis
Intellectual 430 points

Hello,

I have a question regarding the use of 33 ohm resistors as recommended in SLVA531A paragraph 4.3.   If the PHY is placed close to the MAC device (in my case an FPGA) are these series resistors still necessary?  What is the value (33 ohm) based on? Should the PWB traces be 33 ohms as well if the series resistors are used?

Thanks for any help you can give.

  • 0
    TI__Mastermind 31600 points

    The MII connections to the MAC should be 50 Ohm traces.  The MII I/Os are not pure 50 Ohm drivers or loads so the 33 Ohm series terminations improve the impedance matching.  While it is good to keep the traces between the MAC and the PHY short, we still recommend including the series terminations.

    Patrick