Subject: Re: PDA ESD fail
Date: Thu, 19 Dec 2002 12:38:24 +0000 (UTC)
NNTP-Posting-Date: Thu, 19 Dec 2002 12:38:24 +0000 (UTC)
User-Agent: tin/1.5.14-20020926 ("Soil") (UNIX) (Linux/2.4.19 (i686))
Benson Lo wrote:
> The PDA is testing by +/-4KV Contact and +/-8KV Air discharge. But it
> When I use the ESD gun to do contact discharge to the frame ground or
> ground plane. The PDA will reset at +3kV and -0.6KV.
> To protect the PDA from +/-4KV contact discharge, do this means that
> the ground place must resist +/-4KV ?
> Why the negative polarity test is even worst (only -600V) ?
> As the components cannot be placed far away from the frame ground.
> Should I remove the frame ground in the next PCB layout ?
> Should I connect the metal shield of the LCD to the ground. If yes,
> connect to frame ground or ground plane is better ?
As nobody else has taken this, I'll answer it, and possibly get corrected...
If it resets, then something must get into a condition that causes the
micro to be reset.
What is it?
A static impulse causes a current to flow in part of the circuit, often with
very fast rise-times.
This can cause coupling into data lines. If it couples into the address bus,
or various other bits of the circuit, that could cause the processor to
It can also cause ground bounce, especially if you have poorly grounded bits,
which can cause pretty much the same as the above.
Thoughts: what happens if you disconnect the LCD, apart from the ground, does
it still reset when hit with a burst to the screen? If not, that might indicate
that interference is getting into the screen data wires.
If you ground all the pins of the hotsync connector, ...
Might the static be confusing the regulator or reset circuitry, ...
Try adding bits of foil to various bits, and try to understand the results,
or adding ground connections between bits.
Hope this helps.
http://inquisitor.i.am/ | mailto:firstname.lastname@example.org | Ian Stirling.
Get off a shot FAST, this upsets him long enough to let you make your
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