This paper presents a novel topology of DC/DC buck converter which is high power efficiency, low cost and small size. This converter adopts PWM and PFM dual modes control to achieve high efficiency over full load and it works at PWM mode at heavy load, PFM mode at light load. Also time-multiplexing control is accepted to realize two independent outputs with only one 1.1 uH off-chip inductor. The converter is fabricated with CSMC 0.5 um CMOS process, and achieves the peak efficiency with a maximum total output power of 900 mW.