Killertechno
Posts: 177
Joined: Wed Jan 02, 2013 8:28 am

Guidelines for USB bus design for CM

Fri May 31, 2019 5:38 pm

Hi to all!
I'm designing board using Raspberry CM.
I need USB devices such pendrive, USB to serial (I need several serial ports), wireless card....
I found USB hub chip and all devices are USB 2.0; all devices has gor own USB power switch.
I don't need to plug/unplug them, they are all fixed to main board.

I've found a lot of documentation about USB bus design, but in fact it's all for "plug'n'play" items.
As I said, I don't need to plug/unplug devices and I read I just need to follow these rules:
- differential impedance 90 Ohm
- keep at least 1mm away from any kind of ground plane or traces
- keep same trace length as I can
- 27 ohm series reisitor on trace

Ok, any suggested considerations about USB layout for CM?
Thanks.

aBUGSworstnightmare
Posts: 1491
Joined: Tue Jun 30, 2015 1:35 pm

Re: Guidelines for USB bus design for CM

Fri May 31, 2019 5:58 pm

Where did you bet those 'design guide' from? Look for better resource.

As you need multiple USB devices you should start by selecting a USB host chip. Then refer to it's docu for further guideline (as it might include some reference etc.).
What's the background of USB power switch mentioned in your post?

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