The Charge Pump Step-down Switching Power Supply Chip Design

In recent years, almost everyone has at least one portable device, the devices are powered by battery, such as cellphone, portable DVD, PSP, GPS and so on. How to make the battery life time longer is a hot topic for the hardware designer. Using of the high conversion efficiency power management devices is the effective method to prolong the battery life. The inductor based buck regulator is the most popular topology. The buck usually needs a big size inductor and output capacitor to optimize the output noise, but for the portable device, the PCB area reserved for the power management is very limited. The tiny but high efficiency solution is welcomed in this kind of application. The capacitor based switching power can meet the critical requirements.This paper introduced some kinds of power management topologies, has a comparison among them. Introduced the theory of a 1/2 buck charge pump. In order to reduce the output noise to the relative low level, the LDO is employed. As the heart of the LDO, the operational amplifier, band-gap reference and bypass PMOSFET are all introduced.