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TUSB8041: Hub reset design

yf liao
Expert 1080 points
Part Number: TUSB8041

Hi, could you please confirm below questions regarding the reset design for the hub.

1. The max allowed voltage on GRSTz for an active L is 0.8V? What if there is a period of time the voltage is 1V, is the hub in reset state or not?

2. I saw on the EVM board, the GRSTz pin is connected to a 1uF capacitor which means host will not be able to reset the hub via the GRSTz pin. We are wondering if the hub is malfunctional or lost connection to host(such as due to an ESD event), is there a mechanism able to detect this situation and do a warm reset ?

  • 0
    TI__Guru 60870 points
    Hi YF,

    1. The GRSTz is in an undefined state if the voltage is 1V.
    2. The USB host can perform a USB reset to the hub if an error condition is seen, but not a hard reset using GRSTz.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Expert 1080 points

    Hi JMMN,

    Is it possible that a software reset is not working but need a hardware reset, I mean not using GRSTz is a common design?

    Another question, please help me to confirm. Is the max current allowed to flow through the GRSTz internal pull up resistor is 250uA? And what's this pull up resistor value?

  • 0 in reply to yf liao
    TI__Guru 60870 points
    YF,

    No, it is not common to generate a hardware reset to the hub except at power on.

    The GRSTz pin has an internal pullup of 250 uA or max strength of 13.2K.

    Regards,
    JMMN