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

[Rene Harder]

Werner Almesberger wrote:
> Rene Harder wrote:
>   
>> 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.
>>     
>
> Yes, I was hoping that we could have one "universal" filter that's
> suitable for all low-frequency signals (audio, UART, etc.), given
> that most of the noise lives >> 100 MHz and those low-frequency
> signals are << 100 MHz.
>
>   
>> 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.
>>     
>
> That's true, yes. Of course, I fervently hope that we can avoid the
> joy of precision-tuning those filters ;-)
>
>   
>> However, I think we are better off using a single component filter, this
>> decreases complexity and risk of possible misbehavior.
>>     
>
> Great ! 
>
> When we discussed integrated filters, we came up with the following
> components:
>
> Murata NFL18ST (0603, "T"):
> http://search.murata.co.jp/Ceramy/image/img/PDF/ENG/L0112S0119NFL18ST.pdf
>
> Rohm MCF182CN102 (0603, "for power supply"):
> http://www.rohm.com/products/databook/emi/pdf/mcf18.pdf
>
> TDK MEM2012P101R (0805, "Pi"):
> http://www.tdk.co.jp/tefe02/e9617_mem_p.pdf
>
> Which one would be closest to the kind of "universal" filter we're
> looking for ? As usual, smaller would be better :-)
>
>   

I'm still in favor of the pi-filter but let me do another search. Maybe
I'll find a smaller one with similar characteristics  ;-)

>> 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.
>>     
>
> Are we talking about the same part ? R4401 is 220 Ohm and series, while
> the pull-downs in the area (R4416, R4117) are 10 k. Looks more like a
> current-limiter for problem conditions to me.
>
>   

Ups my bad. Unfortunately, I mixed up R4401 with R4404!
Yes this one looks pretty much like a current limiter.