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Linux/TUSB2077A: HUB IC connectivity issue

Nikhil Anjane
Prodigy 90 points
Part Number: TUSB2077A
Other Parts Discussed in Thread: TUSB2036

Tool/software: Linux

Hi,

I have customized boards on which TUSB2077A HUB IC is connected to USB pins of a SOC. The SOC supports for both Andrioid and Linux OS.

The reset circuitry for the active low RESET pin of the TUSB2077A IC  as mentioned on  page 11 of "TUSB2036 and TUSB2077A EVM User's Guide" (sllu190.pdf ) is as follows. 

For both the OS sometimes the USB hub seems to be working perfectly but sometimes the USB connectivity just randomly goes off. On some boards re-flashing the OS brings back the connectivity where as on some the connectivity is still down.

But when I replace the capacitor of 0.1uF with 1uF the USB connectivity is regained.

Can anyone please explain me what exactly is the issue occurring over here? and is there any solution from software side for this issue?

  • 0
    TI__Guru 60870 points
    Nikhil,

    How long is the reset with the 0.1 uF vs. the 1 uF capacitor? The rise time of the 3.3v rail can impact the reset timing.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Prodigy 90 points
    JMMN,

    Thanks for replying.

    With 0.1uF the reset time is 1ms and with 1uF the reset time is 10ms.
    As per the datasheet the reset time should be within 100us to 1ms. Whereas in my case 10ms seems to work.

    Regards,
    Nikhil
  • 0 in reply to Nikhil Anjane
    TI__Guru 60870 points
    Hi Nikhil,

    Is this an embedded system where both the hub and host are powered on simultaneously? It could be that with the shorter reset the hub is mis-interpreting something occurring on the DP/DM lines while the host is still in reset and entering an unknown state. It is difficult to determine without scope plots of the DP/DM lines during the failure.

    When you say that the USB connectivity just randomly goes off - you mean that it sometimes doesn't show up after a power cycle ,or does it actually start out working and then randomly drop off the bus?

    Thanks,
    JMMN
  • 0 in reply to JMMN
    Prodigy 90 points

    Hi JMMN,

    Yes. It is an embedded system where the hub and host are powered on simultaneously. 

    And by USB connectivity randomly going off I mean that, it sometimes doesn't show up after a power cycle.

    Is there any way I can try something through software (OS) where hub initializes in OS?

    Thanks,

    Nikhil

  • 0 in reply to Nikhil Anjane
    TI__Guru 60870 points
    Do you have the ability to generate a software USB reset? That would clear out any issue with the host and the hub being out of sync.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Prodigy 90 points

    Hi JMMN,

    I tried unbinding/binding the USB driver, delaying the USB initialization process in OS and increasing USB response timeout. But, nothing seems to work.

    Regards,

    Nikhil

  • 0 in reply to Nikhil Anjane
    TI__Guru 60870 points
    Can you determine the bus state when this happens? Voltages on DP and DM?