Why does my Inrush Current Limitation not work sufficiently?
You've configured your micro's output for openDrain without internal PullUp/Down, and you think you have this:







simulate this circuit &ndash; Schematic created using CircuitLab

But in all likelihood what you actually have is this:  







simulate this circuit

When you initially power up your circuit, Vcc and GND are at the same potential, so your micro's 'open-drain output' pin will quite happily sink current - and the way you have your external P-FET configured means that it will turn on.  

I suggest that you configure your output pin as push-pull and use it to drive an external N-FET, which then in turn drives the P-FET.
Put a pull-down on the N-FET's gate to ensure that it stays turned off until the micro commands it to turn on.