The LM6x4xx-Q1 uses VCC as its internal power supply. VCC is, in turn, powered from VIN or BIAS. Once the LM6x4xx-Q1 is active, power comes from VIN if BIAS is less than approximately 3.1 V. Power comes from BIAS if BIAS is more than 3.1 V. VCC is typically 3 V to 3.3 V under most conditions, but can be lower if VIN is very low. To prevent unsafe operation, VCC has a UVLO that prevents switching if the internal voltage is too low. See V_{CC_UVLO} and V_{CC_UVLO_HYST} in Section 7.5. During start-up, VCC momentarily exceeds its normal operating voltage until V_{CC_UVLO} is exceeded, then drops to its normal operating voltage. These UVLO values, when combined with the dropout of the LDO when only powering the LM6x4xx-Q1, are used to derive minimum V_{IN_OPERATE} and V_{IN_OP_H}.