A large-current, highly integrated switched-capacitor divider with a dual-branch interleaved topology and light load efficiency improvement

Abstract

Because it is magnet-free and can achieve a high integration level, the switched-capacitor (SC) converter acting as a direct current transformer has many promising applications in modern electronics. However, designing an SC converter with large current capability and high power efficiency is still challenging. This paper proposes a dual-branch SC voltage divider and presents its integrated circuit (IC) implementation. The designed SC converter is capable of driving large current load, thus widening the use of SC converters to high-power applications. This SC converter has a constant conversion ratio of 1/2 and its dual-branch interleaved operation ensures a continuous input current. An effective on-chip gate-driving method using a capacitively coupled floating-voltage level shifter is proposed to drive the all-NMOS power train. Due to the self-powered structure, the flying capacitor itself is also a bootstrap capacitor for gate driving and thus reduces the number of needed components. A digital frequency modulation method is adopted and the switching frequency decreases automatically at light load to improve light load efficiency. The converter IC is implemented using a 180 nm triple-well BCD process. Experimental results verify the effectiveness of the dual-branch interleaved operation and the self-powered gate-driving method. The proposed SC divider can drive up to 4 A load current with 5–12 V input voltage and its power efficiency is as high as 96.5%. At light load, using the proposed optimization method, the power efficiency is improved by 30%.

Keywords

Switched-capacitor converter / Dual branch / Integrated circuit / Bootstrap gate driver

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