[SI-LIST] Re: ESD protection devices

  • From: Nigel Hughes <nigel.hughes@xxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Tue, 14 Oct 2003 11:15:02 +0100

Hi Steve,

huh? - I am surprised that you say that varistors have the slowest response 
of protection devices.  Are you aware of the latest surface mount devices 
like those at http://www.amotech.co.kr/eng/smd_varistor.html.  I find it 
hard to conceive that it is possible they could possible have any more 
inductance than other 0402 components (eg. an 0402 capacitor).  I actually 
have heard the opposite of what you say against non-CSP zeners - ie. die to 
their packaging the die is connected to the package terminals with 
effectively a tiny bit of wire, that introduces a whole heap of 
inductance.  Were you not aware of surface mount varistors?

Cheers,
Nigel.

At 09:44 14/10/2003, steve weir wrote:
>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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=======================================================================
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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