The AIC1639 is a high efficiency step-up DC/DC converter for applications using 1 to 4 battery cells. Only three external components are required to d eliver a fixed output voltage of 2.7, 3.0V, 3.3V, or 5V. The AIC1639 starts up from below 0.9V input with 1mA load. Pulse Frequency Modulation scheme brings optimized performance for applications with light output loading and low input voltages. The output ripple and noise are lower compared with the circuits operating in PSM mode.