Each of the two high-side MOSFET drivers is biased from its floating bootstrap capacitor, which is normally re-charged by V_CC through both the external and internal bootstrap diodes when the low-side MOSFET is turned on. When the TPS55288 operates exclusively in the buck or boost regions, one of the high-side MOSFETs is constantly on. An internal charge path, from VOUT and BOOT2 to BOOT1 or from VIN and BOOT1 to BOOT2, charges the bootstrap capacitor to V_CC so that the high-side MOSFET remains on.