When the input voltage is above the UVLO rising threshold and the EN pin is pulled to a voltage above 1.2 V, the TPS61033 is enabled and starts up. To minimize the inrush current during start up, the TPS61033 has a soft start up function. At the beginning, the TPS61033 enters pre-charge phase and charges the output capacitors with a current of approximately 330 mA when the output voltage is below 0.4 V. When the output voltage is charged above 0.4 V, the output current is changed to having output current capability to drive the 2-Ω resistance load. To minimize the inrush current further, the TPS610333 has a maximum pre-charge current of 900 mA(typical). After the output voltage reaches the input voltage, the TPS61033 starts switching, and the reference voltage ramps up a 0.8 mV/μs. When the voltage at the EN pin is below 0.4 V, the internal enable comparator turns the device into shutdown mode. In the shutdown mode, the device is entirely turned off. The output is disconnected from input power supply.