A Hysteretic Switched-Capacitor DC–DC Converter With Optimal Output Ripple and Fast Transient Response

Hysteretic control is popular for switched-capacitor (SC) dc-dc converters. Conventional hysteretic controllers require either a large output capacitor or high-speed output voltage detection for proper regulation. In this paper, a lower boundary hysteretic control method is proposed which matches the output sampling frequency to the converter switching frequency across the entire load range, hence optimal output voltage ripple can be achieved. The converter responses instantly to step-up load transients that are smaller than six times the initial load current. When larger load transient step occurs, the sampling frequency jumps to its maximum value to recover the output voltage quickly. Small output voltage droop can be achieved while using an output capacitance value on the same order as the converter's charge transferring capacitance. A 1/2 step-down SC dc-dc converter with the proposed control technique is fabricated in 0.18-μm CMOS process. The converter achieves a peak efficiency of 86.4% and delivers a maximum output power of 5 mW.