The 3.3-V LDO from VBUS steps down voltage from VBUS to LDO_3V3 which allows the TPS65988 device to be powered from VBUS when VIN_3V3 is unavailable. This LDO steps down any recommended voltage on the VBUS pin. When VBUS is 20 V, as is allowable by USB PD, the internal circuitry of the TPS65988 device operates without triggering thermal shutdown; however, a significant external load on the LDO_3V3 pin can increase the temperature enough to trigger a thermal shutdown. The VBUS 3.3-V LDO blocks reverse current from LDO_3V3 back to VBUS allowing VBUS to be unpowered when LDO_3V3 is driven from another source. See Table 10-1 for the recommended external capacitance on the VBUS and LDO_3V3 pins.