Being that there is no metal chassis the connector shell most likely has
a direct path to the circuit board. If so, then the HBM ESD pulse of >3
amps is passing through the PCB ground. When the ESD pulse passes
through the PCB ground plane (there is a decent AC path to earth GND
through the "floating" power supply) it can induce signals in the signal
lines that the circuitry interprets as valid signals.
So far the focus has been on reducing the ESD current reaching the
PCB.Another approach to the problem is to reduce the circuit sensitivity
to the ESD pulse.
Trouble shooting in real time (oscilloscopes and such connected to the
circuitry) is a real challenge with ESD. You might instead troubleshoot
the issue by observing what the failure mode is and determining what
circuit nodes, it properly stimulated, would create the failure mode.
Then filtering (as simple as placing capacitors) the suspect nodes may
lead to a solution. The filtering would be more than sufficient to fix
the ESD issue while being less than enough to interfere with normal
circuit operation.
Dave Cuthbert
Micron Technology
From: [email protected] [mailto:[email protected]] On Behalf Of Fred
Townsend
Sent: Wednesday, August 24, 2005 7:14 PM
To: [email protected]
Cc: [email protected]
Subject: Re: ESD help for I/O ports
I don't know what your definition of a 'true ground' is but the facts
are simple. If you share a discharge path with a signal path the
discharge will overwhelm the signal and the device will fail, sometimes
catastrophically. You have obviously created a signal ground. Now create
a discharge ground (i.e. chassis ground). Tie it to your connector
shells but keep it as far away from the signal ground as possible.
Fred Townsend
[email protected] wrote:
>The problem that I have is that my power supply is a class II product.
i.e. I do not have a true ground and also as we all know the printer is
in a plastic box.
>
>thanks
>Pete
>
>
>
>
This message is from the IEEE Product Safety Engineering Society
emc-pstc discussion list. Website: http://www.ieee-pses.org/
To post a message to the list, send your e-mail to [email protected]
Instructions: http://listserv.ieee.org/listserv/request/user-guide.html
List rules: http://www.ieee-pses.org/listrules.html
For help, send mail to the list administrators:
Scott Douglas [email protected]
Mike Cantwell [email protected]
For policy questions, send mail to:
Richard Nute: [email protected]
Jim Bacher: [email protected]
All emc-pstc postings are archived and searchable on the web at:
http://www.ieeecommunities.org/emc-pstc
This message is from the IEEE Product Safety Engineering Society
emc-pstc discussion list. Website: http://www.ieee-pses.org/
To post a message to the list, send your e-mail to [email protected]
Instructions: http://listserv.ieee.org/listserv/request/user-guide.html
List rules: http://www.ieee-pses.org/listrules.html
For help, send mail to the list administrators:
Scott Douglas [email protected]
Mike Cantwell [email protected]
For policy questions, send mail to:
Richard Nute: [email protected]
Jim Bacher: [email protected]
All emc-pstc postings are archived and searchable on the web at:
http://www.ieeecommunities.org/emc-pstc
