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DP83822I: Under timing requirements for RGMII in the DP8322i data sheet, there is a requirement for rise / fall time of max 750ps .. !!! Can it really be right?

Bond - James Bond
Expert 5100 points
Part Number: DP83822I

Customer is measuring  signal integrity / timing on their Ethernet interface where they use the DP83822I PHY.

One of these interfaces runs RGMII 100Mbit.

Under timing requirements for RGMII in the DP8322i data sheet, there is a requirement for rise / fall time of max 750ps .. !!! Can it really be right?

 

I would think the 750ps seem very fast for a 3.3V signal running 25MHz.

If they measure on the outputs from the PHY (RGMII RX port) the signals are closer to 3ns ..

 

Please advise

  • 0
    TI__Mastermind 23675 points
    Mr. Bond,

    You are correct that 750ps is very fast for a 3.3V signal running at 25MHz.
    The DP83822 does not require a 750ps signal. It can operate with a much slower rise/fall time so long that you satisfy setup/hold timing.
    Please ensure you meet the setup/hold timing. Depending on your trace length and load, the rise/fall time will move round.