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TUSB8041-Q1: Unable to connect more than two USB devices when using USB 3.0

Part Number: TUSB8041-Q1

We are using this USB hub (based on TUSB8041IPAPRQ1) . whenever we connect to the USB2.0 port we can detect all four devices.

But when we connect to the USB3.0 port we cannot detect more than 2 devices. On connecting the third device host does not detect the third device or start losing the other one.

Are there any register settings need to be taken care?

All configurations are set as default settings.

  • Hello Rajesh,

    Please note that the power consumption of the hub and device is much higher at USB 3.0 speeds, can you confirm that there is no drooping on the 3.3V, 1.1V or VBUS lines?



  • We measured the voltage for all three points (3.3V, 1.1V and VBUS), there is no voltage drop on those lines.

  • Do you see any difference depending on which port is used?  Can you share a schematic?

  • Thanks for looking into this JMMN, please let me know if that works.

  • Are the series capacitors for the SSTX lines in another part of the schematic?  If you just install 1 or 2 USB 3.0 devices do they work well / consistently?  Do you have adequate solder on the thermal pad below the hub, this can impact device operation especially at higher power states.



  • Hi JMMN,

    Yes, the series capacitors are located in a separate part of the schematic seen in the post above. The SSTX differential pairs each have a 0.1 uF series capacitor and are also filtered with a common mode choke before exiting the USB hub at the connector. 

    With regards to your second question, we were able to achieve consistent operation with 1 USB 3.0 device, intermittent operation with 2, and no operation with the 3rd and 4th devices installed. To clarify, with 4 devices connected, slots 1 and 2 remain operational and slots 3 and 4 are dropped. 

    Our thermal pad has the layout shown below, with the vias sinking to the board ground plane.

    Thank you,

    John Steenstra

  • Hi John,

    Can you confirm that there is adequate solder paste?  We have only seen this kind of behavior if the in-rush current on the downstream devices is high and the VBUS droops or there is inadequate ground pad connection.



  • JMMN,

    Is there any way to check this without removing the IC? Removal would require a heat gun and potentially damage surrounding components. 



  • Hi John,

    I would check for in-rush droop first, many USB devices will drop even if VBUS goes briefly below 4.8V.

    Usually x-ray is easiest to check for solder coverage if that is available.  I agree that removing the IC is not necessary.