I believe you are correct about the peak current - but I cannot say where
the limit would be for your particular application.

It would be interesting if you could conduct destructive testing and post
the results. Monitoring ESR vs load over a period of time.

It has been my experience that I/O ports are difficult to kill. It seems
they tend to degrade to the point that they self limit damage through
high-ish ESR. You will likely be fine so long as you provide adequate time
for the capacitor to change.

I have written firmware for commercial equipment that used PIC16F series
parts directly driving 1nF capacitors (at a 1 second interval) as part of a
level sensing circuit. I never encountered issues or returns - apparently
it worked without excessively damaging the PIC.

On Monday, February 5, 2018, Mario <electron2k4@gmail.com> wrote:

>
> Hello,
> this is for an extremely space-constrained application, so every componen=
t
> counts.
>
> The PIC datasheet specifies what is the max current that can be
> sourced/sinked
> by a PIC pin.
>
> However, this in principle means that no capacitance can be directly
> driven,
> as any capacitor with low ESR (eg. ceramic) will look almost like a short
> circuit, although only for a very brief time.
>
> Regardless of what the datasheet strictly says, in your experience is it
> safe
> to drive a 10nF capacitance directly from a PIC pin (for few hundreds Hz'=
s,
> i.e. without thermal or average current excesses, only peak current), or =
a
> resistor is always needed?
>
> The internal resistance of the pin is in the tens of ohms already, so I
> wonder.
> While the peak current, without the external resistor, will exceed the
> maximum
> specified in the datasheet, this is meant as "continuous current", while
> MOSFETs
> do always exhibit a higher peak current capability.. so why not also PIC
> pins?
>
> Thank you for your insights.
>
> Kind regards,
> Mario
>
> --
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> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>


--=20
Jason White
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