A green-switch controller IC for cascade buck–boost converter with seamless transition over entire input and load range

To raise the utilization ratio of lithium-ion battery in portable devices, a novel green-switch controller IC is proposed to constitute a 4-switch cascade buck–boost prototype, which is capable of outputting non-inverting step down and step up voltages. According to the relations between the input and output voltages through duty ratio, a finite state machine automatically determines the work method of converter namely buck method, boost method or transition method by combining peak and valley current programmed mode so as to improve the line regulation over the entire input voltage range. A three-phase seamless transition method is introduced into the controller. Its additional advantage is to lower output ripples. Furthermore, a special burst mode is added to reduce the power consumption during light-load operation. An elaborately designed circuitry and rigorous stability analysis further improves the seamless performance. The controller IC is designed and fabricated in 1.5 μm BCD (Bipolar-CMOS-DMOS) technology with an area of 8.75 mm2 and applied to a 2.7 V–4.2 V/3.3 V, maximum output power 1.65 W buck–boost converter. It features over 90% conversion efficiency during normal application and still remains over 80% under standby mode. The experimental results show that all functional and performance targets are successfully achieved as expected.

► We design a multi-mode controlled 4-switch cascade buck-boost controller IC.
► Mode transition is realized by identifying duty ratio in current control method.
► Three-phase transition strategy increases line regulation and reduces output ripple.
► Burst mode increases the conversion efficiency under light load condition.
► We do an elaborate circuit design and rigorous stability analysis.