driving high and low side mosfet for synchronous buck converter?
Typically supplying the high side gate driver is accomplished with a "bootstrap capacitor".


While the low side is switched on, the switching node gets pulled low and the capacitor gets charged through the diode. After the low side switches off and the high side switches on, the high side gate driver remains powered by the stored charge. This does limit the maximum duty cycle and minimum switching frequency (as you cannot let the capacitor voltage sag too much), but is cheap and easy to implement.