How to use a N-Channel MOSFET for high side switching?
You will need a voltage that is well above the power rail to supply enough gate voltage to turn the N mosfet full on.
In PWM H-bridges this is often done with a charge pump which is pumped by the PWM cycle.
If you want the N mosfet to be on in a stationary situation you will have to provide that higher voltage by some other means, maybe with a standalone (self oscillating) charge pump.