Ram, Thanks for the interesting information! The HMM model is certainly different and I had not considered that.
I have taken time domain measurements on real HMM and HBM using a Pelligrini target until my hand was hurting (8 kV). The HMM model is really interesting and in real life can be modeled as a 300 ohm transmission line about as long as a human body followed by a higher impedance. The rising edge was faster than our 4 GHz oscilloscope could measure. Now that we have a 12 GHz single-shot 'scope around here our Pelligrini target will be the limiting factor in this measurement. Dave Cuthbert Micron Technology From: Chundru, Ram [mailto:[email protected]] Sent: Thursday, August 25, 2005 10:17 AM To: drcuthbert; [email protected]; [email protected] Cc: [email protected] Subject: RE: ESD help for I/O ports Dave, With all due respect, I would like to make a small point. Human Body Model (HBM) is a model used in component(IC) level ESD testing and it models a charged human discharging through his skin to an IC. The JEDEC JESD22-A114 standard for HBM ESD specifies a peak current of around 0.7 Amps per 1 kV of charging voltage. The model that is used in system level ESD testing is often called Human Metal Model (HMM) which models a charged human discharging through a metallic tool such as a screw driver or a key into a system. The IEC 61000-4-2 is the most widely used system level standard that specifies a peak current of 3.75 Amps per 1 kV of charging voltage. Using the term HBM for system level ESD testing might lead to misunderstanding as HBM is a most widely used model for IC level ESD testing. I have seen many examples. Thanks, Ram Chundru Texas Instruments Inc From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Thursday, August 25, 2005 10:11 AM To: [email protected]; [email protected] Cc: [email protected] Subject: RE: ESD help for I/O ports 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. 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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
