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3220DFP-DGLEVM: 3220DFP-DGLEVM Schematic question

Matt Krolick54
Intellectual 400 points
Part Number: 3220DFP-DGLEVM
Other Parts Discussed in Thread: HD3SS3220

I have question with the INT026 DFP Eval schematics. It seems that on the schematic the TX lines of the HD3SS3220 are connected are connected to the RX lines on the USB C connector and the RX lines of the mux are connected tot he TX lines on the USB C connector.  Is this an error? If not, could you explain this swap?

Thanks,

  • 0
    TI__Genius 16150 points

    Hi Matt,

    It is not an error since according to the the USB type C specification, it seems a little tricky but the cable assembly wiring is as follows:

    Please take a look into the USB type C spec. There you will see that SSRX are connected to SSTX and backwards.

    Best Regards,

    Luis Omar Moran

    High Speed Interface

    SWAT Team

  • 0 in reply to Luis Omar Moran
    Intellectual 400 points

    Thanks for the reply Luis. I understand that the goal is to connect the host's TX to the device's RX and connect the host's RX to the device's TX. In a USB 3.1 type C cable, this "crossover" happens inside the cable, so that goal should be satisfied. So then why is there any swapping of TX and RX between the connectors and the MUX in the INT026 schematic?

    In the datasheet for the MUX, the TXp,TXn,RXp, and RXn lines are described relative to the Host OR Device's Txp,Txn,Rxp, and Rxn respectively. In the schematic for the INT026, there is a TX/RX swap between the USB Type A plug and the input of the MUX and then another TX/RX swap between the output of the MUX and the USB C connector. Was this double crossover done for routing reasons? Can I not simply connect the TX pair of the type A plug to the TX pair of the MUX (and RX of the type A plug to the RX of the mux) and then connect the TX of the mux output to the TX of the USB C connector (and RX of the mux output to the RX of the USB C connector)?

    I also have the UFP version of this eval board (INT027) and in the schematic for that board, TX and RX are not swapped between the connectors and the MUX. Why is there no swapping here?

    Thanks,

  • 0 in reply to Matt Krolick54
    TI__Genius 16150 points

    Hi Matt,

    The HD3SS3220 includes a PASSIVE switch, this is the reason why the signals are swapped, this is because in the layout design these lines must be have a good routing (without aggressive bends). Please take a look into the layout section below:

    Thanks,

    Luis Omar Moran

    High Speed Interface

    SWAT Team

  • 0 in reply to Luis Omar Moran
    Intellectual 400 points
    This is clear. Thank you.