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DP83826AI: DP83826AI MDIO questions

Sean Liao (Yu-Sheng)
Expert 5775 points

Part Number: DP83826AI

Hi sir, 

 

DP83826AI MDIO pin fuctions is mentioned there's internal 10kohm pullup resister in datasheet

But in datasheet, it still mentioned that need a pullup resisitor, and the design checklist also says the external pull up resistor.

 

 

 

The question is that if customer use multiple PHY, there's already internal 10kohm resisitor forms parallel resistance. 

If put more external pull up, it will make the the total resistance value smaller. 

Does it matter? What's the suggestion for multiple PHY?

Thanks a lot!

  • 0
    TI__Guru**** 190461 points

    Hi,

    The internal 10k pull-up resistor is a weak pull up resistor. An external 2.2 k provides much stronger pull-up for a shared MDIO bus, giving faster rise times and ensuring IEEE-compliant timing, especially with if you have multiple PHYs share the same MDC/MDIO bus. I would recommend to add the external 2.2k pullup resistor on the MDIO.

    Thanks

    David