Lpc2000

TomW,
We use a gun and step from a couple of KV to +/-25KV.
All of my connector pins pass though these surge devices
we use called SurgX that will clamp the pulse to 30v and turn
on in about 50ps. My connectors can handle being hit directly.

However our board is mounted in a metal frame which they
also shoot with the gun. At first we had the board isolated from
the frame, but the only way out for the pulse is the ground plane
on the board so it flashes over to the board. (As much as 3/4"!!!)

I stopped this by giving the board a low impedance ground to the
frame so the whole thing bounces up and down as quickly as possible.
This prevents component damage, but still apparently leaves gradients
that will freak out the ARM.

We have a four layer board with both outside layers as ground planes.
As well as inner ground polygons poured around the traces.
A ton of vias stitch the grounds planes together as well.

However I'm still thinking we can get a pretty good gradient between
some of the nets when the board takes a hit. (25kv human body model 
is a lot of bang...)

I also run many of the lines after passing through the surgx devices
through BAV99 diode clamps to both rails.

About all I can do is ground all 4 edges of the board rather than just
the single 1/2" copper tape tail the board has soldered to it now.

As I said we can take 25Kv no sweat it just sometimes crashes the
micro.

With a reliable watchdog it would come right back up.


Landrum Haddix
lhaddix@...
http://web.qx.net/lhaddix