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DP83640 - Pull down on RXD?

Andreas Arnold
Prodigy 100 points
Other Parts Discussed in Thread: DP83640

Hello there,

I am currently designing a schematic that uses the DP83640 as ETH PHY. In the schematic from TMS570LC43x HDK this PHY is also used on page 19. There is a comment that "strongly recommends" to add a 2k2 pull-down resistor.

Does this apply only for use in RMII mode when these signals are unused. Or is it always recommended? Also in MII-mode?

Regards, Andreas Arnold

  • 0
    TI__Mastermind 23675 points

    Hi Andreas,

    It is recommended to add external pulls because the internal ones are weak (10k ohms and higher). 

    This is not a requirement to add them, but we see that customers like to add stuffing option just in case there is some parasitic resistance on the board.

    Kind regards,

    Ross

  • 0 in reply to Ross Pimentel
    Prodigy 100 points
    Hey Ross,

    thanks for your answer. Is this recommendation for all RXD[0:3] or only for the RXD[2] and RDX[3] as stated on the Hercules Dev Kit?
    And what about the TXD? Is there also a recommendation for any pulls?

    Regards, Andreas
  • 0 in reply to Andreas Arnold
    TI__Mastermind 23675 points

    Hi Andreas,

    I would recommend pulls if your connected MAC has pulls that do not align with the configuration you intend to use. 

    TXD and RXD do not need external pulls because there are internal ones, but if you have space of see that the connected equipment is pulling the pin in the wrong direction then I would recommend adding a footprint to stuff the resistors.

    Kind regards,

    Ross