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I am in the middle of making a small USB & LAN pass through PCB (a small add-on PCB for a larger project.)

I have some problems getting it to work properly. It is quite simple - it takes a USB signal from one connector to another, and that is that.

I know USB needs 90Ohm differential impedance (+-15%.)

The layout looks like this where the 2 highlighted lines are the USB data lines:

enter image description hereenter image description here

The PCB is a 0.8mm board, and for getting 90 ohms I have the differential trace to be 0.8mm wide with 0.2mm space - that gives me 83.605 ohms which is well within the 15% tolerance.

What can else be a problem with the layout? I kept the track on the bottom side of the PCB to avoid unwanted stubs on the connector.

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  • \$\begingroup\$ Your ground, on the top layer has some discontinuities (asymmetry) near the uab connector. But even in this case I wouldn't worry too much, it's probably good enough for usb 2.0 \$\endgroup\$
    – Mike
    Commented Jun 12, 2017 at 15:07
  • \$\begingroup\$ Well, I have some problem, that when I use this, my device will detect the USB for a short while, and then disconnect - \$\endgroup\$
    – M.Egsdal
    Commented Jun 13, 2017 at 6:32
  • \$\begingroup\$ I'm not sure why some are saying the USB D+/D- are swapped. Those are clearly two different connectors. That leads me to believe one is USB-A and the other is USB-B per the standard. Which means the D+ and D- are correct. Did you find a solution? If so please post it here because this is a good question. \$\endgroup\$ Commented Mar 22, 2020 at 12:49

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I suspect that the way you have wired it from one connector to the other hasn't taken into account that you need to swap D+ and D- over i.e. you have inadvertently inverted the data. You may also need to do this for ground and Vcc.

It's impossible to be more certain given that you haven't shown a schematic.

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  • \$\begingroup\$ My first thought as well, though the bottom looks more like a header than a connector - hard to tell either way \$\endgroup\$
    – W5VO
    Commented Jun 12, 2017 at 13:08
  • \$\begingroup\$ Well, the schematic is quiet simple - oi65.tinypic.com/2vte05y.jpg It uses a internal to external USB connector like this: cpc.farnell.com/akasa/exusbie-40/… Right now if i try to use it as it is Well, I have some problem, that when I use this, my device will detect the USB for a short while, and then disconnect - \$\endgroup\$
    – M.Egsdal
    Commented Jun 13, 2017 at 6:28
  • \$\begingroup\$ There are four pins connecting to four more pins and they transport GND, +V, -D and +D. I believe you have highlighted -D and +D. Please either properly identify them on your schematic or just swap over -D and +D and see if it works. \$\endgroup\$
    – Andy aka
    Commented Jun 13, 2017 at 6:34

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