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TUSB8040A1

Peter Tinodi
Prodigy 20 points
Other Parts Discussed in Thread: TUSB8040A1

Dear TI!

I'd like to design a special USB 3.0 HUB with the TUSB8040A1.

My problem is, that in some designs I found the RX and TX pair mixed up. I mean the IC's downstream USB_SSRXx_xxx port was connected to the USB connector's TX pin, and the SSTX... to the RX pin.

It is a normal USB 3.0 "A type" female connector and if I swipe the RX and TX at the IC's downstream port and connect the RX pin to the connectors's TX, should it be correct?

Here are 2 designs, which sould be correct? ( the normal has the connector at the bottom, the cross on the top)

https://dl.dropboxusercontent.com/u/126286420/cross.jpg

https://dl.dropboxusercontent.com/u/126286420/normal.jpg

Thanks,

Peter

  • 0
    TI__Expert 4055 points

    Hi Peter,

    Per USB3.0 spec, it is permissible to swap the positive and the negative of each differential pair (meaning: to swap 'RX+ with RX-' and 'TX+ with TX-' ), however it is not permissible to swap RX lines with TX lines. Actually in the 2 designs you posted I don't see the the RX lines being swapped with the TX lines as you described, what I see is RX+ being swapped with RX- and TX+ with TX- which is permissible.

    Additionally, on the designs you posted, are they following the 'less than 5 mils difference between a SS differential pair signal and its complement' rule (I see a bigger mismatch)?  Please make sure to follow the 'TUSB8040A1 Design Guide' (http://www.ti.com/lit/an/slla341a/slla341a.pdf) for a proper implementation.

    Please let me know if you have any questions or comments.

    Best Regards,

    Alexis Cortes.

  • 0 in reply to Alexis Cortes9585
    Prodigy 20 points

    Hi Alexis,

    thank you for your answer, I'll fix the distance between the differencial pairs.

    But my original question still stands. On the "cross" screenshot the RX pairs connect to the upper (pin 5 and 6) pins, and the USB connector is on the top side of the PCB.

    However on the other "normal" screenshot the connector is at the bottom side of the PCB, and the RX pairs connect to the pins 8 and 9.

    So you are saying that the IC's downstream RX shoud be connectedto the connectors's RX pins, like on the pic bellow:

    http://www.addonics.com/technologies/images/usb3_usb3A_pinout_lrg.jpg

    sorry for being so uncomprehending :)

    thanks, Peter

  • 0 in reply to Peter Tinodi
    TI__Expert 4055 points

    Hi Peter,

    If you are using a standard USB connector (which I think you are), you should connect the RX differential pair from the TUSB8040A1 to the RX differential pair of the connector and the same for TX (RX with RX, TX with TX).

    Best Regards,

    Alexis Cortes.