The XC9223/XC9224 series are synchronous step-down DC/DC converters with a 0.21 (TYP.) P-channel driver transistor and a synchronous 0.23 (TYP.) N-channel switching transistor built-in. A highly efficient and stable current can be supplied up to 1.0A by reducing ON resistance of the built-in transistor. With a high switching frequency of 1.0MHz or 2.0MHz, a small inductor is selectable; therefore, the XC9223/XC9224 series are ideally suited to applications with height limitation such as HDD or space-saving applications. Current limit value can be chosen either 1.2A (MIN.) when the LIM pin is high level, or 0.6A (MIN.) when the LIM pin is low level for using the power supply which current limit value differs such as USB or AC adapter. With the MODE/SYNC pin, the XC9223/XC9224 series provide mode selection of the fixed PWM control or automatically switching current limit PFM/PWM control. As for preventing unwanted switching noise, the XC9223/XC9224 series can be synchronized with an external clock signal within the range of 25% toward an internal clock signal via the MODE/SYNC pin. For protection against heat damage of the ICs, the XC9223/XC9224 series build in three protection functions: integral latch protection, thermal shutdown, and short-circuit protection. With the built-in U.V.L.O. (Under Voltage Lock Out) function, the internal P-channel driver transistor is forced OFF when input voltage becomes 1.8V or lower. The XC9223B/XC9224B series' detector function monitors the discretional voltage by external resistors.