AVR-Chat

Hmmm.   It's beginning to sound like a crap-shoot.    The device I'm
specifically looking at protecting is an AVR uC, its I/O lines specifically.
How would you do it, if I may ask?   The environment is a boat one,
basically an automobile one (engines, pumps, motors) with the added features
of local radar, VHF and HF radio transmissions, as well as wireless computer
and instrument transmissions.  Lightning too.   Shielded cables are a given,
as is spike suppression on inductive loads.   Thanks, Steve

 

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of wagnerj@proaxis.com
Sent: Thursday, January 06, 2011 8:36 AM
To: AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] AVX Transguard

 

  

You need to look at the tolerance specs. And, it depends, greatly, on what
the connected electronics will tolerate.

I just looked up the AVX parts, and they are spec'd a bit differently from
some of the others. The 3.3V parts are rated for a 5.0V +/-20% breakdown.
That means anywhere from 4.0V to 6.0V. with a "clamping" voltage of 12V at
1A.

If you look at the V-I chart in the spec sheet, it shows that the 3.3V
ones have a forward current of (about) 100ua at 3.3V, 1ma at 5V, 10ma at
about 6V, 100ma at maybe 7V, and 1A at around 8V.

So, they are NOT really "open" at 3.3V and not really breaking down at 5V.
So, your other circuitry had better be able to handle more than 6V!

The thing you will be relying on is that ESD has a pretty large source
impedance (some K ohms for human body model) and a source capacitance of
some 1000s of pf. Thus, the ability to source high currents is very
limited. This is what saves the circuit, in the end.

Jim




://www.eset.com



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