The AT1391 provides complete control and protection for a DC/DC converter optimized for high-performance microprocessor applications. It is designed to drive one P-Channel in a buck topology. The AT1391 integrates all of the control, output adjustment, and protection functions into a single package. The output voltage of the converter can be precisely regulated with a maximum tolerance of 2% over temperature and line voltage variations. The AT1391 is a family of low-noise step-down DC/DC converters that is ideally suited for systems powered from a 1-cell Li-ion battery or from a 3-cell to 4-cell NiCd, NiMH, or alkaline battery. It can also be used to USB-Based power system.