The driver of the HS switch requires a bias voltage higher than the V_IN voltage. The capacitor, C_BOOT in the 简化版原理图, connected between CBOOT and SW pins works as a charge pump to boost voltage on the CBOOT pin to (V_SW + V_CC). A boot diode is integrated on the die to minimize external component count. TI recommends a high-quality 0.47-µF, 6.3-V or higher voltage ceramic capacitor for C_BOOT. The V_{BOOT_UVLO} threshold is designed to maintain proper HS switch operation. If the C_BOOT is not charged above this voltage with respect to SW, the device initiates a charging sequence using the LS switch before turning on the HS switch.