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DP83822I: MDIO pullup resistor

Koshi Ninomiya
Expert 5435 points
Part Number: DP83822I
Other Parts Discussed in Thread: AM2432,

Tool/software:

Dear Team,

My customer is evaluating the DP83822I with AM2432 (PRU unit MDIO: no pull).
Under the pullup resistor of MDIO of the DP83822I is 4.7kΩ, when power is turned on, the PHY register value cannnot be read stably. This phenomenon is rare.

When they changed the pullup resistor value from 4.7kΩ to 2.2kΩ according to the DP83822I datasheet, this phenomenon was solved.

Why is the MDIO pullup resistor value 2.2kΩ?
if the MDIO pullup resistor value was 4.7kΩ, what issue can you think of?

Best Regards,

Koshi Ninomiya

  • +1
    TI__Mastermind 24988 points

    Hi Ninomiya-san,

    There are two requirements to consider for MDIO PU value:

    1) VIL and VIH logic thresholds for valid MDIO communication



    2) SMI timing requirements

    2.2kΩ is recommended as it typically satisfies these conditions, relative to internal MDIO pin termination, and typical driving strength of MAC/PHY.

    For 4.7kΩ, I suspect there is a setup/hold time violation. This can be verified by probing MDIO waveform during SMI transaction.

    Thank you,
    Evan