Vic, An unpowered product does not have the ground wire (green wire) in the power cord as an AC powered system (such as a PC) does. So, the ESD current injected into the unpowered prodcut does not have a direct conductive path to the ground plane and back to the ESD generator. This is the reason why the unpowered prodcut should not be grounded during ESD testing. As there is no ground connection during the test, we need to remove the charges off the system before the next zap. Otherwise due to the residual charges on the system, the ESD generator can not fully discharge on the next zap. There are different methods to remove the charges: use a conductive brush and brush off the charges between zaps, make a momentary ground connection thru a 1 MOhm resistor between zaps, etc. If you are concerned about the possibility of discharges from the human body into the pins, the person touching the pin extender could wear a ground strap. This way, the pins will not receive any unwanted human ESD. Thanks, Ram Chundru System Level ESD Engineer Texas Instruments.
_____ From: [email protected] on behalf of Vic Gibling-NonTRW Sent: Fri 8/18/2006 6:43 AM To: [email protected] Subject: ESD testing - automotive Dear colleagues, The unpowered product is required to be insulated from the ground plane. The product is NOT grounded. It is subjected to a number of discharges at a rate of 1 - 10 seconds. If the charge does not neutralise before the next discharge what happens and why is this test done in this manner? The same product (and arrangement) receives discharges to each connector pin. To ease applying the discharge to small pins a short single pin extender is used. The procedure is to remove the extender after fulfilling the discharge requirements and use it for the next. It is removed by hand. Any comments? I would appreciate your views and comments. Vic Vagabond EMC Engineer - 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/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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ - ---------------------------------------------------------------- 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/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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
