[gta02-core] ECN0032 (EMI and ESD protection for headset jack)

Rene Harder rehar at saweb.de
Wed Oct 7 20:37:11 CEST 2009

Werner Almesberger wrote:
> Rene, we discussed using a single filter component instead of a discrete
> "pi" configuration. What's your opinion ? I'm a bit concerned that we
> may end up with a lot of components to place in this already crowded
> area, and risk getting unexpected secondary effects.
I totally understand your concerns those discrete pi-filters introduce a
bunch of new components into the circuit with many possible side effects.
My main idea of using discrete filters though, was to keep new
components (with different packages) as small as possible to reduce SMT
assembly cost.
Also you are more flexible with a discrete filter than with a single
component one; If we mess things up, we can just replace the caps or the
inductor and fix the problem but with a single component filter we would
need a different one and might need to change the pcb pattern as well.

However, I think we are better off using a single component filter, this
decreases complexity and risk of possible misbehavior.

> Also, do we still need C4405 ? If I understand things correctly, it just
> stands guard against general EMI badness, but since we have a real filter
> now, it can only make things worse, no ? ECN0032 mentions its removal,
> but the schematic still has it.

I must have missed this one.

> R4401 is for general DC protection ?

I've no idea what the purpose of this resistor is/was. This seems to be
an ordinary pull-down resistor but for what I can't tell for sure.
Nothing makes completely sense to me.

> By the way, if we replace the pis with integrated filters, we should
> have enough room to draw the various stages such that they don't
> overlap, i.e., one (virtual) rectangle with the jack, one with all the
> TVSs, one with all the filters, and then all the rest, including the
> branch JACK_INSERT branch. That should make the whole affair look a bit
> less intimidating.

Agree! Right now it looks kind of ugly, I was already thinking of moving
some sub circuits to a separate sheet.


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