When the input voltage is applied, the high side MOSFET is turned on. The input voltage charges the output capacitors through the inductor and the high side MOSFET. When the output capacitors are charged to 0.83-V typical value, the TPS61322xx starts switching at 1.6-MHz fixed frequency and the high-side MOSFET is turned off. When the output voltage goes up to typical 1.6 V, an internal soft-start control circuit ramps the reference voltage to 0.8 V within 2 ms. In this way, the soft-start function reduces the input inrush current. After the output voltage reaches the target value, soft start ends, and the inductor peak current is determined by the output of an internal error amplifier. After start-up, the TPS61322xx can work with the input voltage down to 0.4 V.