[SI-LIST] Re: ESD protection devices

  • From: Geoff Stokes <gstokes@xxxxxxxxx>
  • To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
  • Date: Tue, 14 Oct 2003 10:22:14 +0100

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
> >=============================================================
> ==========
> >
> >
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