Highly-­Integrated Switched­-Capacitor DC­-DC Converters

The increasing demand for power converters with high energy efficiency and power density has sparked interest in highly-­integrated switched-­capacitor converters to replace traditional inductor-­based switch-­mode power supplies. The switched-­capacitor converter leverages the benefits of capacitors offering increased energy density compared to inductors and superior power switch utilization to that of inductor­-based switch-­mode power supplies. By integrating power switches, gate­drivers, and digital control circuits, and utilizing high energy density MLC capacitors, larger output power can be achieved while maintaining a high power density through monolithic integration. This research focuses on fixed­ratio DC­-DC converters, particularly in the context of a DC bus for 48 V­12 V, common in various applications. The developed design methodology optimizes power switch sizing considering intrinsic and parasitic capacitance losses. Additionally, the optimization of external flying capacitors is presented. Experimental results of a fabricated IC implementing a 4:1 Ladder topology with integrated switches, gate­drivers and digital clock control demonstrate the effectiveness of the design methodology. The measured peak efficiency for the 48 V­12 V highly-­integrated switched-capacitor converter is 93.5 %, achieving a maximum output power of 24.6 W, leading to a maximum power density of 23 W/cm³. Addressing startup challenges, three proposed solutions, consisting of a passive startup strategy, a switch­-conductance control strategy, and an active pre­charge circuit strategy, have been simulated and the active pre­charge circuit has been validated experimentally, with the active pre­charge circuit ensuring that the peak inrush current of the 48 V­12 V highly-­integrated switched­-capacitor converter is only 534 mA. Furthermore, this research explores hybrid switched­-capacitor converters, eliminating charge redistribution losses of the flying capacitors to enhance energy efficiency and power density. A visual multi­step approach and an equivalent output resistance analysis for non­idealities have been developed to examine the soft­charging capabilities of hybrid switched­capacitor converters. In conclusion, this study demonstrates the potential of highly-­integrated switched-­capacitor converters to meet the increasing demands of high energy efficiency and power density in consumer electronics, offering promising solutions for future power conversion technologies.