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DP83867IR: Power Sequencing

Brian Angiel
Expert 4060 points
Part Number: DP83867IR

I am currently working on a design with several DP83867IRRGZ. I have some questions regarding power sequencing.

 

For power reduction I am required to shut down any power supplies used by the Ethernet PHY when they are not in use. Currently I have dedicated 2.5V and 1.0V power supplies that only connect to the DP83867. The VDDIO pins are connected to a 1.8V power supply shared by the rest of the design.

 

My first thought was to run in three-supply mode since I've already got a 1.8V supply on the card, but there's some slightly confusing notes in the datasheet regarding power sequencing. In three-supply mode I believe that VDDA1P8 should not be left powered when 2.5V and 1.0V are shut down - so this is why I'm looking at two-supply mode.

 

My understanding is that in two-supply mode I should leave VDDA1P8 open and the datasheet implies there are no sequencing requirements. In this mode is it okay to leave the VDDIO pins powered (1.8V) if power supplies sourcing VDDA2P5 and VDDA1P0 are shut down?

 

Thanks for your help!

Brian

  • 0
    TI__Mastermind 18425 points
    Hi Brian,

    Yes, in two supplies mode, VDDA1P8 should be left open. They should also not be shorted together. Having VDDIO present without VDDA2P5 and VDDA1P0 should be ok. Will this be for extended periods of time or just a power sequencing issue? We haven't done targeted characterization where only VDDIO is present. If you are planning to run the system in this condition for extended periods of time then I would recommend in-system testing.

    -Regards
    Aniruddha