ESD

[Andy Green]

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Somebody in the thread at some point said:
>> If the GPS is normal, I think the RF switch circuit (ESD sensitive) is
>> complete break-down.
> 
> While talking about ESD:
> To me it seems, BATTEMP, headset-connector (i.E. HOLD, JACKINSERT), outer 
> plane of touchscreen (XL,XR | YU,YL ?), and of course debug connector, all 
> could use some ESD protection. As well as GPS-ext-ant, it seems (U7606,1. 
> Yeah i know, RF).
> Ok, i didn't check the specs of the CPU pins that get the impact, but IIRC 
> there was a statement of 4kV ESD surge resistance for the GTA. I guess any 
> complex chip will be better off not to take this.

I just woke up -- and talk about GTA02 only -- but JACK_INSERT at least
has 10K series resistor and a 1K to 0V I believe from the audio amp
side, so this should be no problems.  HOLD I would have to check.

Debug connector is probably OK since it is normally NC and does not come
out of the case.

BATTEMP IIRC also has a series resistor as part of the network and one
to 0V so it should be OK.

Touchscreen is a good point, although again I think it is inherently a
high impedence path.

GPS I will look at later, I guess there is some matching network at
least between it and the chip.

The impedence matters because it affects what is actually seen by the
protection diodes in the chips it connects to.  It is a lot easier for
them to shrug off an ESD event via 10K than directly.

But Joerg, this is good stuff to read someone is worrying about!

- -Andy
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