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TUSB4041I: USB-Hub permanently connected to Host-Computer

Christopher Bechthold
Prodigy 20 points
Part Number: TUSB4041I

Dear TI-Support,

i am trying to figure out if the TUSB4041 is causing a problem in our system.
The system consists of a host PC and a daughter card connected through a backplane.
On the daughter card we designed the TUSB4041 to be self-powered, i.e. the TUSB4041 remains in-active as long as the daughter cards power switch isn't turned on.

The observed failure is as follows:
When the daughter card is switched on, sometimes the USB device tree in Windows disappears and all USB peripherals are no longer available.

The data lines between host PC and TUSB4041 are permanently connected, even during GRSTz = 0.
We guess that during this state the host PC may be sending data causing problems.
The host PC may detect a short-circuit event by mistake and switches off its USB controller.

My questions are ...

Related to the USB2.0 specification may the data lines be permanently connected to each other?
I could not find anything in the specification or i am still missing it.

Which state do the differential transceiver have during GRSTz asserted low? High-Z?

Do you recommend to set AUTOENz/HS_SUSPEND = 0?

Thank you in advance.

Regards,

Christopher

  • 0
    TI__Guru 60870 points

    Hi Christopher,

    When the USB device tree disappears, it doesn't reappear?  It will sometimes disappear briefly during a re-enumeration event.  Permanently connecting the host and hub is acceptable, and the DP/DM lines should be high-Z during reset.  AUTOENz/HS_SUSPEND is only valid if the system is using downstream battery charging, I would recommend not enabling auto mode unless specifically required.

    If the host PC sees an overcurrent, it should report that as an error.  Are you using a Microsoft OS?  Can you install usbview.exe or usb device tree viewer and post a before and after screenshot to help debug?

    Regards,

    JMMN

  • 0 in reply to JMMN
    Prodigy 20 points

    Thanks for your reply.

    To clarify, only after the daughter cards main switch has been actuated do all voltage regulators start up.
    VDD and VDD33 are only present after the card has been switched on, but DP/DM are permanently connected to the host PC.

    We thought this might be a problem. If the TUSB4041 is unpowered, the host PC could still send data.
    Due to the internal protection diodes, the host PC could detect an overcurrent situation.

    We are using Windows. Unfortunately the Hub does not re-appear.

    Unfortunately, the error rarely occurs. But I will install usbview and try to provide you some screenshots.

    We will also leave AUTOENz/HS_SUSPEND = 1.

    Regards,

    Christopher

  • 0 in reply to Christopher Bechthold
    TI__Guru 60870 points

    Hi Christopher,

    Have you been able to duplicate the issue and get a screenshot?  Also, can you check if the host is backdriving voltage into the hub through DP/DM?  It should not since the host should have pulldowns on DP/DM, but I would like to confirm it.

    Regards,

    JMMN

  • 0 in reply to JMMN
    TI__Guru 60870 points

    Closing ticket for now, just post a response to reopen it.

    Thanks,

    JMMN