Nigel, Steve I would add that protection devices always degrade the system performance somewhat. Transzorbs have a capacitance of 1000pF or more at a few volts, so are not normally suitable for signal bandwidths of greater than around 1 MHz. The protection sometimes has to be a compromise, using shielding, resistors and diodes for high speed interfaces, with special consideration to ESD return currents via protection diodes and filtering in the power supplies. RF people use filtering such as a shunt choke and/or sometimes spark-gap devices to achieve low capacitance, or special low capacitance limiter diodes which are not appropriate for DC coupled or low frequency applications. Regards Geoff > -----Original Message----- > From: steve weir [mailto:weirsp@xxxxxxxxxx] > Sent: 14 October 2003 09:45 > To: nigel.hughes@xxxxxxxxxx; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: ESD protection devices > > > Nigel, varistors have the slowest response of available > devices as they > have always been fairly inductive. Varistors also have > traditionally had > the least well controlled hold and breakdown voltage > tolerances. General > purpose zeners have a soft VI curve, and limited energy handling > capacity. Transzorb type devices are the most expensive but > handle high > energy surges, have comparatively very flat VI curves, low > inductance, but > alas higher prices. Vendors have device performance curves > and lots of > application notes. > > At 09:30 AM 10/14/2003 +0100, Nigel Hughes wrote: > >Hello Forum, > > > >I am trying to compare and evaluate ESD protection devices. > According to > >the device physics, what are the things that limit the speed > at which a > >zener or varistor responds? I have heard previously that a varistor > >responds quicker but read that the device itself is damaged > when an ESD > >event passes through it. However others say that with the > new multi-layer > >structure of surface mount devices, the damage is negligible > (if occurring > >at all). Has anybody got a better perspective of what the > truth actually > >is. A bit of background supporting information would be helpful. > > > >Thanks, > >Nigel. > > > >============================================================= > ========== > >O O O Nigel Hughes Tel +44 1763 266266 > >O O O Terminals Fax +44 1763 261216 > >O O O TTPCom Ltd. > > Melbourn Science Park, Cambridge Rd., Melbourn, > Royston, Herts > >SG8 6HQ UK > > nigel.hughes@xxxxxxxxxx > >============================================================= > ========== > > > > > >------------------------------------------------------------------ > >To unsubscribe from si-list: > >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > >or to administer your membership from a web page, go to: > >//www.freelists.org/webpage/si-list > > > >For help: > >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > >List archives are viewable at: > > //www.freelists.org/archives/si-list > >or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > >Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > _________________________________________________________ Zetex Semiconductors - Solutions for an analog world EID Award Winners for 'Best Use of Technology' 2003 for the AcoustarTM ZXCW8100 End-to-End Digital Audio Amplifier Controller http://www.zetex.com _________________________________________________________ ###################################################################### E-MAILS are susceptible to interference. You should not assume that the contents originated from the sender or the Zetex Group or that they have been accurately reproduced from their original form. Zetex accepts no responsibility for information, errors or omissions in this e-mail nor for its use or misuse nor for any act committed or omitted in connection with this communication. If in doubt, please verify the authenticity with the sender. ###################################################################### ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu