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USB non-buspowered GND - what to do

Started by Tobias Alte July 22, 2004
Hi,

I'm currently working on a selfpowered USB device and have just a quick
question.
Maybe I overlooked/missed some info on the datasheets etc. but I am
questioning
myself what to do with the GND coming from the USB host. My device has its
own
supply so I don't need the USB supply.

Should I connect the USB bus GND to the GND at the board for EMV purposes
( and leave USB +5V unconnected ) or must I connect none of the USB supply
pins
with the device if I use a external supply ?

Thx for advice.


Tobias Alte wrote:

> Hi, > > I'm currently working on a selfpowered USB device and have just a quick > question. > Maybe I overlooked/missed some info on the datasheets etc. but I am > questioning > myself what to do with the GND coming from the USB host. My device has its > own > supply so I don't need the USB supply. > > Should I connect the USB bus GND to the GND at the board for EMV purposes > ( and leave USB +5V unconnected ) or must I connect none of the USB supply > pins > with the device if I use a external supply ? > > Thx for advice.
Of course you must connect the GND. At least you need it as a potentail reference for the USB signals. -- Reinhardt Behm, Nauheim, Germany, reinhardt.behm@t-online.de
Reinardt Behm wrote
> > Of course you must connect the GND. At least you need it as a potentail > reference for the USB signals. > > -- > Reinhardt Behm, Nauheim, Germany, reinhardt.behm@t-online.de >
Thanks.
"Tobias Alte" <tobias_alte@web.de> wrote in message
news:cdp2t5$kq4$05$1@news.t-online.com...
> I'm currently working on a selfpowered USB device and have just a quick > question. > Maybe I overlooked/missed some info on the datasheets etc. but I am > questioning > myself what to do with the GND coming from the USB host. My device has its > own > supply so I don't need the USB supply.
If you are new to electrical engineering, I'd suggest reading up on Kirchoff's Current Law and Kirchoff's Voltage Law. If you are NOT new to electrical engineering, I'd suggest reading up on Kirchoff's Current Law and Kirchoff's Voltage Law. :-) --Keith Brafford Embedded Excellence, Inc.
"Reinardt Behm" <reinhardt.behm@t-online.de> wrote in message
news:v8apdc.732.ln@main.behm.eae.de...
> Tobias Alte wrote: > > > Hi, > > > > I'm currently working on a selfpowered USB device and have just a quick > > question. > > Maybe I overlooked/missed some info on the datasheets etc. but I am > > questioning > > myself what to do with the GND coming from the USB host. My device has
its
> > own > > supply so I don't need the USB supply. > > > > Should I connect the USB bus GND to the GND at the board for EMV
purposes
> > ( and leave USB +5V unconnected ) or must I connect none of the USB
supply
> > pins > > with the device if I use a external supply ? > > > > Thx for advice. > > Of course you must connect the GND. At least you need it as a potentail > reference for the USB signals. >
You do? With differential signals?
On Sun, 25 Jul 2004 11:07:18 GMT, "steven" <stevenPANTSvh@pandora.be>
wrote:

>"Reinardt Behm" <reinhardt.behm@t-online.de> wrote in message >news:v8apdc.732.ln@main.behm.eae.de... >> Tobias Alte wrote: >> >> > Hi, >> > >> > I'm currently working on a selfpowered USB device and have just a quick >> > question. >> > Maybe I overlooked/missed some info on the datasheets etc. but I am >> > questioning >> > myself what to do with the GND coming from the USB host. My device has >its >> > own >> > supply so I don't need the USB supply. >> > >> > Should I connect the USB bus GND to the GND at the board for EMV >purposes >> > ( and leave USB +5V unconnected ) or must I connect none of the USB >supply >> > pins >> > with the device if I use a external supply ? >> > >> > Thx for advice. >> >> Of course you must connect the GND. At least you need it as a potentail >> reference for the USB signals. >> > >You do? With differential signals? >
Yes, in practice you do. Unless one gavanicaly isolate one side, one need to keep the grounds of the different systems with 30V (On RS-485 anyway). I am not sure what the common mode range for USB is. Regards Anton Erasmus