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TUSB8044A: Power up sequence

Takahiro Saito
Expert 5455 points
Part Number: TUSB8044A


Hi team,

Is there any problem to input signal from up/downstream before USB HUB IC is powered up?

Regards,

Saito

  • 0
    TI__Guru 60870 points

    Saito-san,

    Do you mean USB signals?  For the host this is not a problem, but the downstream devices can possibly backdrive voltage into the hub, so an active reset on GRSTz would be recommended to ensure a clean power on reset condition when the USB Hub IC is powered.

    Regards,

    JMMN

  • 0 in reply to JMMN
    TI__Expert 5455 points

    Hi JMMN-san,

    >Do you mean USB signals? 

    Yes.

    Is the backdrive voltage possibly cause of the incorrect operation of hub IC? Do you just concern about the backdrive voltage test in the USB compliance test?

    I just want to clarify. The signal from up/downstream doesn't damage the device when the power isn't supplied to hub IC. Is that correct?

    Regards,

    Saito

      

  • 0 in reply to Takahiro Saito
    TI__Guru 60870 points

    Hi Saito-san,

    The main concern with backdriving voltage through DP/DM lines has to do with the hub possibly not getting a good power on reset, rather than damage.

    Regards,

    JMMN