[gta02-core] SD/SIM vs. ESD and EMI

Werner Almesberger werner at openmoko.org
Tue Dec 1 13:59:19 CET 2009

Patryk Benderz wrote:
> but i believe that it is wise to
> design PCB in a way, that you can apply fixes later - as history of
> GTA-02 teaches us ;)

Heh, definitely :-)

The issue here is that gta02-core (like GTA02) doesn't have ESD
protection on the SD/SIM holder. This is against the book, but I
think we got away with it because one will almost certainly touch
one of the grounded metal covers before reaching the SD or SIM
contacts, and thus be free from any electrostatic charge.

Of course, we shouldn't rely on such things. So my question is
if the electrical properties of a TVS (transient voltage
suppressor) are such that we could put TSVs in lieu of the
capacitors that we already have on those lines, in case we want
to improve the ESD protection.

If this is at least theoretically feasible, then we don't have
to worry about the issue for now and are thus one step closer to
finishing the schematics.

(The question actually goes beyond this, because if a TVS acts
like a regular capacitor, then it would be even wrong to just
put a TVS in parallel to a capacitor without adjusting the
capacitor's value accordingly.)

- Werner

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