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HD3SS3220: USB-C DFP RX/TX connection discrepancy between TI reference designs.

Michael Hwang
Prodigy 30 points
Part Number: HD3SS3220

Hi,

I'm confused about how to route the RX/TX lines for a USB-C downstream facing port.

In the datasheet (https://www.ti.com/lit/ds/symlink/hd3ss3220.pdf?ts=1623202734779), you get this:

but in the evaluation module (https://www.ti.com/lit/ug/sllu237a/sllu237a.pdf?ts=1623269991422), the RX goes to the TX pin and vice versa, and the AC coupling caps are on the RX lines:

What is the correct way to route the RX/TX lines, and where do I put the coupling capacitors?

  • +1
    TI__Guru**** 176811 points

    Hi,

    Both are correct. The HD3SS3220 is a passive switch, so it is possible to swap its TX & RX pins, you only have to care about the appropriate routing direction between the HOST and the connector.

    The AC coupling caps must be placed on TX, the typical value is 0.1uF. The AC coupling caps on RX are optional and typical value is 0.33uF. You only need to place the caps on one side of the HD3SS3220 as long as the common mode voltage is within the HD3SS3220 spec of 0-2V. I would recommend placing the caps on the connector side.

    Thanks

    David