How to drive a high side mosfet with the L6388E driver?
This driver is a high and low side driver meant to work in continuous switching applications.  It uses a bootstrap technique, meaning that the OUT pin has to be pulled to ground regularly to keep the bootstrap cap charging.  

If you try to turn the high side on and keep it on you will not charge the bootstrap cap and therefore will not have enough high side voltage to turn on the FET.  The UVLO on Vboot will not allow the driver to operate.

There are high side FET drivers with charge pumps built in for on/off switch type applications, you might want to look at those.  Here's one example: Microchip HS driver