Posts: 190
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?

Posts: 1576
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?

Return to “Compute Module”