But back onto my original question:
What is the formula for determining current draw of a PWM circuit?
For example, If I was using PWM on an LED, with the PWM Frequency at 1KHz and it's duty cycle at 50%, what is the current draw?
Generally, it's quite straightforward to calculate the average current draw, as it is just the PWM percentage of the max. current. At 50% duty cycle it's half, at 10% it's 10% and so on, but... It still needs to be able to handle the max. current.
A regular 20mA LED can be used with that "formula", increasing the current, but don't go below 2% duty cycle (with an average draw of 20mA, i.e. 1A pulses), as the bonding wires will either melt or rip off of the crystal with too high currents, even if the average is low.
The IXDN404PI is a MOSFET driver, not a motor driver and the 4A will only be sustained some tens of ns and only with a large enough potential. The max. peak pulse current is very dependant on the voltage potential (in all drivers). At 1 kHz, the chip won't be able to sustain anywhere near 4A and, as dunk
mentioned, even the 1A is dependant on your ability to keep it's cool.
For a simple, but quite effective, heatsink, a bit of aluminum curtain rail can be glued onto the IC with a small
drop of super glue.
If something reliable (for driving motors) is wanted, use a motor driver instead.