> ... circuit is a 14.4V battery powering an LM2594M
> through a FDN5618P p-channel MOSFET and a 3R9 0805
> resistor. The input to the regulator has a 33uF electrolytic
> in parallel with a 100nF ceramic. The battery remains
> disconnected from the circuit until the user presses a
> button. It is controlled by a 16F73 that keeps the circuit
> powered up after the button is pressed. Current draw from
> the circuit in normal operation is between 40mA and 90mA.

Lets try some lateral thinking.
Why is this a 3R9?
It MAY be a surge protector to protect following circuitry.
It doesn't have much voltage drop across it in normal operation.
If it is feeding a regulator and voltage drop doesn't matter why not
increase its value?

That said, it is running "closer to the wind" in normal use than is ideally
ideal.
90 MA x 3R9 = 351 mW = 30% of abs max for Philips part with no temperature
elevation above ambient.

These people make "pulse resisting" versions (0805 and larger) and the
graphs suggest you want a larger part :-(

    http://www.irctt.com/pdf_files/PWCAPPLICATIONNOTE.pdf



        RM

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