A high efficiency current mode step-up/step-down DC-DC converter with smooth transition

This paper presents a current mode step-up/step-down DC-DC converter with small output voltage ripple, high efficiency, and fast transient response. When the input voltage is much higher or lower than the output voltage, the converter operates in peak current pure buck mode or valley current pure boost mode to reduce the switching loss. Double lossless current sense circuits are adopted to improve the current sensing speed. Two transition modes are introduced between buck mode and boost mode to alleviate output voltage ripple. Moreover, the average inductor current is also minimized to reduce the conduction loss in two transition modes. The converter has been designed with a 0.5μm CMOS process. The recovery time is less than 200μs with a switching frequency of 400 kHz when the load current switches between 300mA and 600mA. A peak efficiency of 94% is achieved, and the maximum output voltage ripple is less than 25mV.