Author Topic: Routing USB Between PCBs  (Read 1428 times)

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Offline braddrew0Topic starter

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Routing USB Between PCBs
« on: October 13, 2019, 09:55:13 am »
Hey All,

I need to route a USB signal between two PCBs. The rough flow looks like USB port > board 1 > some plug > cable > some plug > board two > USB PHY. I'm planning to use standard 5 core USB cable for the cable, but I'm coming up short trying to find a suitable plug. Has anyone had to do this before, and/or can recommend something that might work? The signal is up to USB HS (480 MBps) - and yes, I understand this is probably well outside USB spec (although if there was an in spec answer that isn't using a hub/standard USB cable between the two) I'd be interested to hear.

Thanks!
 

Offline sokoloff

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Re: Routing USB Between PCBs
« Reply #1 on: October 13, 2019, 09:58:35 am »
They come off millions of desktop motherboards worldwide on DuPont style headers, right?
 
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Offline tooki

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Re: Routing USB Between PCBs
« Reply #2 on: October 13, 2019, 10:35:04 am »
...although if there was an in spec answer that isn't using a hub/standard USB cable between the two) I'd be interested to hear.
Why not use a standard cable, e.g. micro USB?

But as sokoloff said, you can just use any old headers for the connectors. While the cable itself really should be USB cable*, the connectors aren’t critical.

*Internal USB is routed through PCB traces and all kinds of cables. For low-speed USB it probably isn’t critical at all. For full-speed and high-speed, chances are the design of the traces or cables matters, so it’s easier to just buy USB cable rather than to learn and try to implement the specs.
 

Offline T3sl4co1l

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Re: Routing USB Between PCBs
« Reply #3 on: October 13, 2019, 10:58:25 am »
What do you mean by "two PCBs", are they stacked boards in an assembly?  Different PCBs inside a common enclosure?  Completely separate projects?

In the first case, plain headers are fine, even for high speed.

In the second case, the aforementioned Dupont style (or Molex SL, or...) is fine; a shielded cable is greatly preferred, but the shield termination into the connector probably doesn't need to be too tight.

In the third case, fully shielded connectors and cable should be used.

Note that hybrid cases are common: a PC might have #2's solution from the motherboard to a front panel connector (which is grounded to the metal chassis), then #3's solution to the outside world (regular USB cables and devices).  The key is having ground planes available for shielding.  (The assumption in #1's solution, is that the boards are both ground plane based designs, and the headers have multiple ground pins to ensure those grounds are well bonded through the connector.)

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline braddrew0Topic starter

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Re: Routing USB Between PCBs
« Reply #4 on: October 14, 2019, 07:00:42 pm »
Thanks guys! :)
 


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