The XC9251 series are 30 V operation step-down DC/DC converter ICs with an internal driver transistor. The internal Nch driver transistor is driven by bootstrap to achieve a stable, high-efficiency power supply up to an output current of 2.0 A. Low ESR capacitors such as ceramic capacitors can be used for the load capacitor (CL). A 0.8 V reference-voltage source is incorporated in the IC, and the output voltage can be set to a value from 1.2 V to 12.0 V using external resistors (RFB1, RFB2). 300 kHz or 500 kHz can be selected for the switching frequency. The generation of unneeded noise can be suppressed by synchronizing to an external CLK in a range of ±25% of the free-running frequency using the SYNC pin. In automatic PWM/PFM control, the IC operates by PFM control when the load is light to achieve high-efficiency over the full-load range from light to heavy. The soft-start time can be set as desired by adding an external capacitance to the SS pin. With the built-in UVLO function, the driver transistor is forced OFF when input voltage becomes 4.5 V or lower. Internal protection circuits include overcurrent, integral latch, and short-circuit protection, and thermal shutdown circuits to enable safe use.