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DP83867CR: Rise/fall time spec in RGMII mode

John11513
Expert 5720 points
Part Number: DP83867CR

Hi,

DP83867CR datasheet specifies the rise/fall time of RGMII interface as below 0.75ns while does not mention the test condition. Can any one tell me the test condition of this spec? (especially with what kind of load resistance/capacitance the test is done) 

A customer told me their test result violates this spec. They tested the TR/TF of RX_CLK (in RGMII mode) with 1GHz probe + 13GHz scope and 1870mil of trace. The test result is TR= 1.13ns, TF=0.93ns. I am not sure if this is due to improper test setup, or test condition.

Thank you,

John

  • 0
    TI__Mastermind 18425 points
    Hi John,

    The load capacitance for RGMII traces is 5pF max. Can you check with customer if the scope had low capacitance? Also the capacitance added by the traces should be taken into account.

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    TI__Expert 5720 points
    Hi Aniruddha,

    Thank you for reply!
    However i think it is very difficult to keep the load capacitance below 5pF. The scope probe typically has 3.9pF input capacitance, in addition to MAC pin and pcb trace pin capacitance, it is basically impossible to control the load capacitance below 5pF I think.
    I am guessing if you misunderstanded my question? (my question is the test condition of RGMII timing specs, instead of the input capacitance spec of RGMII pins).
    Thank you,
    John
  • 0 in reply to John11513
    TI__Mastermind 18425 points
    Hi John,

    Apologies, I think I did misunderstand the question. What test condition were you referring to? Voltage and Temperature? In that case the time spec should be met under all voltages and temperatures applicable to the PHY variant that the customer is using.

    -Regards,
    Aniruddha