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TUSB4041I: Crystal Oscillator Not Oscillating

Thuan Vu
Intellectual 460 points
Part Number: TUSB4041I

Is the crystal oscillator suppose to ALWAYS be oscillating? Does the device automatically stop driving the cyrstal?

I am trying to verify the crystal oscillator but can't see the oscillation on an oscilloscope(1 pF active probe). The hub enumerates. Behavior is the same if I have no devices attached or 1 Flash drive attached.

Pin configuration mode by default:

SMBUSz = floating

AUTOENz = floating

FULLPWRMGMTz = 4K7 to GND

GANGED = 4K7 to 3V3

PWRCTL_POL = floating

SCL = 1K5 to 3V3

SDA = 1K5 to 3V3

  • 0
    TI__Guru 60870 points

    Hi Thuan,

    The crystal will stop when the hub is suspended or not connected to a host.

    If a host is connected to the hub, but there are no downstream devices connected the host will often suspend the hub.

    Are the hub / downstream device enumerating correctly or not?

    I sent you a friend request if you want to share your schematic offline.

    Regards,

    JMMN

  • 0
    TI__Guru*** 145905 points

     what crystal are  you using? did you follow the instruction mentioned in datasheet?

  • 0 in reply to JMMN
    Intellectual 460 points

    Hub is enumerating correctly.

    1 downstream device tested and enumerated correctly.

    No oscillation detected with host connected and no device or with device.

    Is there a way to keep the hub from being suspended? Even with straps on board? We need to send board to crystal vendor to get characterized so need constant oscillation.

  • 0 in reply to Brian Zhou
    Intellectual 460 points

    Crystal: ECS-240-18-20BQ-DS-TR

    We think 33 pF for the load capacitors is too high so we changed it to 20 pF but still did not see oscillations.

  • 0 in reply to Thuan Vu
    TI__Guru 60870 points

    Hi Thuan,

    Where are you probing the clock?  Can you attach a USB flash device to the hub and access it (data transfer test or similar) or connect a USB mouse while probing the crystal? The clock will be running.  There is no way to force the hub out of low power state on the board.  You can try setting SMBUSz low, this may keep the crystal running but will prevent normal hub operation if a SMBUS host is not used.

    Regards,

    JMMN

  • 0 in reply to JMMN
    Intellectual 460 points

    Tried another USB device(headset) and the crystal oscillates constantly.