A 10-MHz 2-800-mA 0.5-1.5-V 90% Peak Efficiency Time-Based Buck Converter With Seamless Transition Between PWM/PFM Modes

Abstract

Time-based controllers are well suited for implementing both single- and multi-phase wide bandwidth high switching frequency pulsewidth modulation (PWM)-based dc-dc converters. They also consume very little quiescent current but their light load efficiency is severely degraded by switching losses. We explore pulse frequency modulation (PFM) that is commonly used to improve light load efficiency in voltage-mode controllers and extend its operation to time-based controllers. To maintain high efficiency even in the presence of dynamic load variations, we present techniques to perform automatic and seamless switching between PWM/PFM modes. Fabricated in a 65-nm CMOS, the prototype buck converter using the time-based PWM/PFM control achieves 90% peak efficiency and >80% efficiency over a load current range of 2-800 mA. Output voltage changes by less than 40 mV during PWM to PFM transitions.