I'm sure it may have been mentioned, but current out of the pin could
also be an issue if you do not include a resistor in series. I wouldn't
rely on the current limit of the PIC output while changing states.
--
Martin K


Tom Stamm wrote:
> Markus,
> FETs can be VERY fast devices. They can easily become oscillators if any 
> inductance (nanohenries...) appears in the source lead, including the 
> inductance of the bonding wire and pin.
>
> The oscillating L-C circuit consists of the gate-to-drain capacitance 
> and the source inductance. Frequency may be in the tens or hundreds of 
> megahertz. The oscillation may or may not occur, depending on the Q of 
> the circuit. Lossy circuits don't oscillate. Less lossy circuits may do 
> damped ringing on turnon and turnoff.
>
> The 100 ohm resistor damps the oscillation. It's a VERY good idea to 
> include it in any FET circuit that switches current on and off. For very 
> fast switching, such as switching regulators, the resistor may have to 
> be tuned to compromise between switching speed and the tendancy to ring.
>
>   

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