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Original question:

TUSB8020B: Hub input supply current

TUSB8020B: Tsu_io and Thd_io timing requirement

Yen Nee Lee
Prodigy 120 points
Part Number: TUSB8020B

Hi,

We have external 4.7kOhm pull down on pin 36 (FULLPWRMGMTzSMBA1/SS_UP). Below is what measured on board. 

- Pin36 is measured to be 0.85V before reset released. Is this expected?

- Based on the datasheet at 7.6 Power-Up Timing Requirements, the Tsu_io and Thd_io are measured with respect to GRSTz's VIH or VIL?

- Based on the scope capture below do you see any issue? The pin36 goes low while reset is released.

Green=VDD3v3, Blue=VDD1V2, yellow=GRSTZ, RED=FULLPWR

Thanks.

  • 0
    TI__Guru 60870 points

    Hi Yen Nee Lee,

    Yes, this is expected behavior since the FULLPWRMGMTz pin has an internal pullup that is +/-225 uA (max).  850 mV seems a little high, I would expect the real value at the pin to be closer to 800 mV.  The TUSB8020B should be able to sample the input low properly.  I don't see any issue here.

    Tsu_io and Thd_io are mesaured with respect to GRSTZ Vih.

    Pin36 will go low after it has been sampled and it becomes a status output (SS_UP).

    Regards,

    JMMN