Re: [SI-LIST] : Interesting ESD devices

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From: Mark Fex (mafex@sympatico.ca)
Date: Fri Aug 18 2000 - 06:14:54 PDT


Hi Doug et al.

I design PCB artwork and am in the midst of laying out a PCI I/O card that
will handle RS232/422/485 data protocols. This card will have two channels
available and the protocol, address, and interrupt of the card will all be
software selectable ( no jumpers).

Currently, my client has elected to go with a bundled ESD suppression
device ( 8 channels in one device ) shared between the two DB9 I/O
connectors.

I have been plugging individual devices ( 0805packages ) as close as
possible to the connectors to maximize their effect.

Aside from the obvious advantages of immediate proximity to the connectors,
I was curious to see if anyone has any ideas about other issues that I should
be aware of that may diminish the effectiveness of the ESD suppression
devices. I was thinking about wider traces ( larger than .012" ) and the effect
of vias in the circuit path ( I use .040 OD with .020 ID ).

This design will be a 4 layer board with the inner layers used for +5V and
ground.

Thanks in advance for any advice....

Regards,

Mark

Mark Fex
International Circuits
Windsor, Ontario / Detroit, Michigan
519-948-5334

On 13 Aug 00, at 21:40, Douglas C. Smith wrote:

> Hi Peter et al.
>
> When using devices such as these, even if they are perfect
> (infinitely fast clamp to zero volts with zero series
> resistance), a path on a multilayer board connecting to the
> devices can have significant voltage drop. 5
> volts/millimeter inductive drop from an ESD event is easily
> obtained and exceeded! Layout is VERY important.
>
> Devices such as these can prevent damage if properly used.
> However, data corruption on the protected lines is still
> likely to occur and must be handled by other design
> techniques. In quite a few cases, these techniques can
> eliminate the need for the protective devices in the first
> place.
>
> Doug
>
> Peter Baxter wrote:
> >
> > Hi Avi,
> >
> > Take a look at Bussmann's SURGEX parts and Littelfuses PULSEGUARD parts.
> >
> > Very low capacitance, around 1pf. 0805, 0603 or strips to suit DB
> > connectors. Be aware that they have more styles available than shown on
> > their promotional material.
> >
> > I found Littelfuse to be very helpful.
> >
> > Regards,
> >
> > Peter Baxter
> >
> > Date: Wed, 9 Aug 2000 08:03:12 +0300
> > From: Greenhut Avi-BCMS17 <Avi_Greenhut-BCMS17@email.mot.com>
> > Subject: [SI-LIST] : Guideline comparison between ESD devices
> >
> > I am looking for the ESD guideline that includes the following
> > information:
> >
> > 1. Type of ESD component devices that are available in the market.
> > 2. The ESD component devices application.
> > 3. Comparison between the types according to the applications.
> >
> > Avi Greenhut
> > Motorola Communication Israel
> > 3 Kremenetski Street P.O.B 25016 Tel - Aviv 67899 Israel
> > Tel: 972-3-565-8795 , Fax: 972-3-565-8778
> > E-mail: BCMS17@email.mot.com
> >
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> --
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> ___ _ Doug Smith
> \ / ) P.O. Box 1457
> ========= Los Gatos, CA 95031-1457
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> / /\ \ ] / /\ \ Mobile: 408-858-4528
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