The bootstrap capacitor between the BST and SW pin supplies the gate current to charge the high-side FET device gate during the turnon of each cycle and also supplies charge for the bootstrap capacitor. The recommended value of the bootstrap capacitor is 20 nF to 200 nF. C_BST should be a good quality, low-ESR ceramic capacitor located at the pins of the device to minimize potentially damaging voltage transients caused by trace inductance. A value of 100 nF is selected for this design example.