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TUSB8041: USB compliance if not using 5V switch for VBUS

franziskus
Expert 7769 points
Part Number: TUSB8041

Team,

my customer is using TUSB8041 in a new design. The device is directly connected to a CPU with its upstream ports. There is no connector etc.
Only the data signals are connected, there is no switchable upstream VBUS voltage. The USB_VBUS pin of the hub is directly connected to the 5V supply on the board.

Is this setup USB compliant?
How do they need to handle USB_VBUS to be USB compliant?

The TI EVM uses a VBUS switch between hub and CPU. Is this needed?
Is the connector that is used on the EVM also needed?

What's the recommended circuitry for the hub if it is directly connected to the upstream port without having a complete USB-host with VBUS?

Thanks!

  • 0
    TI__Guru*** 131275 points
    can you send schematic or block diagram to us?
  • 0 in reply to Brian Zhou
    TI__Expert 7769 points
    Thanks for your reply Brian!
    I have sent more information via email.
    I will report the solution here in case we solve it offline.
  • 0 in reply to franziskus
    TI__Expert 7769 points
    Team,
    thanks for your help. This is the answer we have found offline:
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    It is acceptable to have USB_VBUS pulled high at all times if the hub will always be connected to a powered host. Please be aware that the DCP / ACP charging modes can never be enabled if USB_VBUS is always on. Routing between the host and the hub can be done directly, making sure each side has the required AC caps on the USB3.0 TX pair near each transmitter.

    I would recommend an active reset to the USB hub to prevent any unexpected states between the host and the hub during power on reset. We have seen some USB hosts attempt to access the USB hub before it has enabled its termination and drop to compliance mode.
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