The AIC1578 is a high performance step-down DC/DC converter, designed to drive an external P-channel MOSFET to generate programmable output voltages. Two main schemes of PulseSkipping and Pulse-Frequency Modulation are employed to maintain low quiescent current and high conversion efficiency under wide ranges of input voltage and loading condition. The AIC1578 delivers 10mA to 2A of output current with 87%~93% efficiency at VIN=9V, VOUT=5V condition. A current sense comparator with both inverting and non-inverting input uncommitted is included to provide the crucial function of either current limit protection or constant output current control. When the AIC1578 is used in a high-side current sensing step-down constant current source, the efficiency is typically greater than 90%. Duty cycle can be adjusted to greater than 90% by connecting a resistor from DUTY pin to VIN. Quiescent current is about 90A and can be reduced to 8A in shutdown mode. Switching frequency being in around 90KHz to 280KHz range, small size switching components are ideal for battery powered portable equipment.