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I want to use the USB 2.0 multiplexer TI TS3USB221ARSER. But on the PCB the D+ and D- pins of one connection are crossed (see attached image). USB pins crossed

Is it okay to change the D+ and D- pins on all sides of the multiplexer to fix this? The two alternatives are:

  • use a via on one signal trace to switch to the other side (I always read one should avoid vias in high speed connections?)

  • avoid this problem with long connections (see second attached image. Trace lengths/trace impedance not calculated in the image). USB solution2

Which is the best solution?

Thanks!

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    \$\begingroup\$ I can't see that this would be a problem. There's no indication in the datasheet that the sets of pins are handled differently - just as long as you remember to switch them on all 3 ports... \$\endgroup\$
    – brhans
    Commented Dec 19, 2014 at 21:33
  • \$\begingroup\$ Alright, thanks! What if switching pins on all sides means that on another side the traces are crossed? Is it better to use a via or to expand the trace lengths and take the solution from the second image? \$\endgroup\$
    – Martin
    Commented Dec 19, 2014 at 21:42
  • \$\begingroup\$ My gut feel would be to use the longer but matched traces for high-speed USB. If you're only going up to full-speed then the via would probably be ok. \$\endgroup\$
    – brhans
    Commented Dec 19, 2014 at 21:59

2 Answers 2

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The only way I can see this being a problem is if this switch waits for the end of a USB frame to perform the switch -- although signaling is differential, end-of-frame and start-of-frame events are denoted with DC levels (e.g. D- high and D+ low).

But I doubt this is the case and it's probably fine to swap.

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Unless it is explicitly specified in IC datasheet, swapping D+/D- will not work.

I have used vias with D+/D- before but I created them for both traces so that length and general characteristics stay the same. Having via on only single one will be ok if traces are kept very short, but I personally like to avoid it.

My personal approach would be to to use longer, matched traces.

PS: Assumption is that this is for High speed (480 Mbps) USB 2.0. If you are dealing with Full speed (12 Mbps) or slower, you can pretty much do anything.

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