[email protected] wrote (in <[email protected]>) about 'ESD help for I/O ports', on Thu, 25 Aug 2005: >Being that there is no metal chassis the connector shell most likely >has a direct path to the circuit board.
Well, preferably not. But if it HAS to go to the board, it should go by a wire (as thick as is practicable, to get the lowest inductance) to the point that has the lowest impedance (normally the highest capacitance) to earth. >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. Yes, but by connecting the external metalwork to the highest-capacitance point, the current mostly flows to ground that way and not through ground traces on the board. > >So far the focus has been on reducing the ESD current reaching the PCB. Ye, because usually that is the most dependable and explicable solution. -- Regards, John Woodgate, OOO - Own Opinions Only. Deadlines are 90% of deadliness. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk 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
