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TUSB8041: What is the rise/fall time requirement on TUSB8041 GRSTz signal

Peng Liu50174
Expert 1500 points
Part Number: TUSB8041

Tool/software:

Hi, Experts,

On our circuit board, the TUSB8041 GRSTz pin is connected to host processor with one RC filtering network.

In the TUSB8041 datasheet, on page 10, section 7.5 Electrical Characteristics, 3.3-V I/O, there is one input transition time of 25ns max. Is this limit also applicable to GRSTz signal with hysteresis feature?

Thanks,

Peng,

  • 0
    TI__Guru*** 145435 points

    Hi Peng:

        There is pullup resistor on GRST pin inside hub, you only need  external 1uf cap on GRStz pin, or you can control with external GPIO signal.

    Best

    Brian

  • 0
    Expert 1500 points

    Hi, Brian,

    If only having 1 external 1uF capacitor, according to datasheet note on page 11 "(2) There is no power-on relationship between VDD33 and VDD unless GRSTz is only connected to a capacitor to GND. Then VDD must be stable minimum of 10 μs before the VDD33". On our circuit board, VDD is powered up later than VDD33. So external RC delay is added to GRSTz to meet 3ms Td2 requirement.

    The question is when GRSTz rising time is more than 3ms (far more than 25ns transition time in table 7.5), can this cause issue on functions/performance/reliability of this hub chip?

    Thanks,

    Peng

  • +1 in reply to Peng Liu50174
    TI__Guru*** 145435 points

    Hi Peng:

        Only  Input hysteresis will affect GRSTz pin, slow rising edge will not affect functions/performance/reliability of this hub chip .

    Best

    Brian