A Low Ripple Fully Integrated Switched Capacitor Buck Converter Employing Time Interleaving And Pulse Frequency Modulation Techniques

A fully-integrated switched capacitor buck converter implemented in the ON-Semi 0.5-[mu]m technology, that converts a 3.3 VDC to 1.5 VDC while driving up to a 8-mA current load. A symmetric charge-discharge topology for capacitors is devised for low ripple. Ultra-low output ripple is achieved through time-interleaving. It is observed in simulation that a ripple of 100 mV on a baseline design can be reduced to 6 mV by implemented 4-phase time-interleaving with a symmetric topology. To achieve high efficiencies at lower loads, a burst-mode pulse-frequency modulation (PFM) technique is implemented. A multi-layer layout technique is used for bucket capacitor to reduce the effect to parasitic capacitances, thereby increasing the efficiency of the circuit. To integrate more capacitance in less area on-chip, the tank capacitor is implemented as a MOSCAP. Maximum measured efficiency of 68% is achieved at 8 mA current load. Measured output voltage ripple less than 28 mV is maintained for current loads between 8 mA and 500 [mu]A.