USB Design Suggestion

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by KaraMuraT on Thu Jul 01 00:10:22 MST 2010
My question is not exactly related to LPCXpresso software platform (since I successfuly applied the USBCDC example). It is about the instability.

I know software is working because at rare rates I successfully executed my prototype. But the problem is, success is really rare. I get usually "USB device not recognized." error. Sometimes it starts to enumerate, but fails later.

Exact thing happened with also an FTDI FT232RL based design. This shows me that I know something clearly wrong and it is related to hardware.

So I need your precious suggestions about layout and schematics design.

By the way, I'm working on a hand made (etched plate) prototype. All passive measurements are OK, no shortcuts, no cut routes.

As a clue, sometimes I see the "eye" formation with USBDM and USBDP, but if it will not work, I see a low signal for about 25 ms on these signals. Than it says "USB not recognized".

Any help is appreciated. Related file is attached to this message.

P.S: Right now I'm testing it with USB Mass Storage Mode for firmware update. I'm getting same unstable results. This clearly indicates that is a non-software problem. (I succeeded to see firmware.bin  on some other PC's)