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TUSB8041 connected to TUSB9261

Travis Estep
Prodigy 60 points
Other Parts Discussed in Thread: TUSB8041, TUSB9261

I am currently working on a device which will mount to the back of a Microsoft Surface Pro 3. This device will extend the capabilities of the Surface by providing 3 additional USB 3 ports using the TUSB8041 and also by providing additional storage using a SATA Solid State drive connected via the TUSB9261.

The Surface Pro only has one USB port. This means that I will have to connect the TUSB9261 directly to one of the downstream ports of the TUSB8041. Are there any recommendations for interfacing 2 USB 3 on the same PCB without the use of traditional USB connectors?

To make my request clear, I want to have both the TUSB8041 and the TUSB9261 on the same PCB. I want to connect the upstream port of the TUSB9261 to one of the downstream ports of the TUSB8041 on the PCB.

Are there any special termination considerations? Do I just route the traces as I normally would when using the correct connectors, but instead just place traces instead of connectors? Are there any impedance considerations? Is this a bad idea altogether? Are there other ways of accomplishing this without having 2 boards for these 2 chips?

Any guidance is MUCH appreciated!

  • 0
    TI__Guru 60870 points
    Hi Travis,

    It is fine to route the devices on the same board. You will need to have 90 ohm differential impedance like all USB traces. You will need the series capacitors on both sets of SS pairs and you will need to cross the SS pairs (RX to TX) in the layout since it won't be done by the cable. Also, to meet USB compliance requirements you will need to mark the TUSB8041 port where the TUSB9261 is connected as non-removable. Functionally, this doesn't do anything but it is required for USB logo and WHQL.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Prodigy 60 points

    Thanks for the info. Just to make sure my schematic is correct, the SSRX pins from one chip will route to the SSTX pins of the other chip, correct? Is there a position on the board that is best to cross the pairs, such as close to the chip or at the coupling caps?

  • 0 in reply to JMMN
    Prodigy 60 points
    Also, is it still permissible to swap the SSTX_P and SSTX_N traces to avoid having to also cross those? Do the chips auto-detect that and take that into account, or is there a firmware that I have to load in order for that to work?
  • 0 in reply to Travis Estep
    TI__Guru 60870 points
    Superspeed lines can handle polarity swapping without any addtional configuration. The RX of the upstream port needs to connect to the TX of the downstream port, and the TX of the upstream port needs to connect to the RX of the downstream port. The TX series caps should be near the transmitter on each side.