The LM3645 has an internal comparator that monitors the voltage at IN and forces the LM3645 into standby if the input voltage drops to 2.2 V. If the UVLO monitor threshold is tripped, the UVLO flag bit is set in the VOLT_FAULT Register (bit [7] in reg 0x15). If the input voltage rises above 2.2 V, LM3645 is not available for operation until there is an I²C read of the VOLT_FAULT_REG Register (0x15). Upon a read, the Flags1 register is cleared, and normal operation can resume if the input voltage is greater than 2.3 V.