The bootstrap capacitor between the BOOT pin and the SW pin supplies the gate current to turn on the N-channel MOSFET. The recommended value of this capacitor is 10 nF and should be a good quality, low-ESR ceramic capacitor. In some cases, it can be desirable to slow down the turn-on of the internal power MOSFET to reduce EMI. This can be done by placing a small resistor in series with the C_boot capacitor. Resistors in the range of 10 Ω to 50 Ω can be used. This technique should only be used when absolutely necessary, because it will increase switching losses and thereby reduce efficiency.