USB non-buspowered GND - what to do

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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.



Re: USB non-buspowered GND - what to do

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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


Re: USB non-buspowered GND - what to do

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Thanks.



Re: USB non-buspowered GND - what to do
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its
purposes
supply

You do? With differential signals?



Re: USB non-buspowered GND - what to do

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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


Re: USB non-buspowered GND - what to do
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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.



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