Amund -
Thanks for the question. As you can guess, it is difficult to offer
detailed
advise without knowing your design, product, price sensitivity, etc. However,
you are in luck- this forum has never hesitated to offer advice on any topic
or problem, regardless of knowledge...!! ;)
Below please find
a) serious technical advice, and
b) humor, or at least an attempt at it.
<begin serious technical advice>
I have three items that can be checked. I have found that these cover about
90% of *RESET* from ESD:
Whenever I see a RESET of a microprocessor (microcontroller, CODEC, etc.)
during ESD testing, the first thing I check is the schematic. Look for any
pins on the micro-P that are floating. It can be an I/O pin, or a RESET pin,
or any pin. I have solved many an ESD RESET problem by connecting floating
pins. Some pins can be grounded, others may need to be connected to power or
pulled high through resistors- check the data sheet for the micro-P. Using
this method the pins are no longer floating and have higher ESD immunity.
The second thing to check for any RESET problem is to see if you have a
"glitch-filter" on the RESET pin. This is a simple RC circuit that adds a
time constant to your RESET signal. It will add a low pass filter to the
RESET signal. This will allow the normal RESET to occur, but a fast transient
such as ESD will be filtered. Generally this is a series resistor with a cap
to GND, but "glitch-filter" configuration depends on your RESET logic (active
HIGH or active LOW).
A third thing to check is the code for your micro-P. Make sure that the
interrupt table is 100% filled with NOPs and IRET instructions. I have seen
cases where the ESD causes an interrupt but the interrupt vector points to an
empty interrupt table- thus causing random code to generate and eventually a
lock-up or a RESET from the watch-dog timer.
<end serious advice>
<begin tongue-in-cheek epilog>
Epilog #1:
BTW- the above advice usually costs USD$1200/day from a consultant- but we
here at the EMC-PSTC forum offer it for free: we believe that all internet
citizens should have access to better ESD health care. Actually, we have
started a committee to form a plan to create a drawer statement highlighting
the key points of our outward facing proposal for a new committee.
Epilog #2:
If the above helps, make sure to donate some of your advice back to the forum.
Don't think you have nothing to contribute- sometimes I wonder about my own
contributions...
<end tongue-in-cheek>
Hope the serious advice helps, and the humor is tolerable..
-Patrick
From: [email protected] [mailto:[email protected]] On Behalf Of Amund Westin
Sent: Tuesday, May 25, 2010 4:15 PM
To: [email protected]
Subject: ESD - some basic hints pls
I have a 24VDC operated ITE / radio unit.
It fails on 6kV (contact discharge) applied to RX port. Microprocessor
restarts.
Any basic advice how to protect the unit? I have no ground in my system.
Best regards
Amund
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-
This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<[email protected]>
All emc-pstc postings are archived and searchable on the web at:
http://www.ieeecommunities.org/emc-pstc
Graphics (in well-used formats), large files, etc. can be posted to that URL.
Website: http://www.ieee-pses.org/
Instructions: http://listserv.ieee.org/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:
Jim Bacher: <[email protected]>
David Heald: <[email protected]>
