Adaptive switching frequency scaling digital controller for improving efficiency of battery powered dc-dc converters

This paper introduces a practical system for improving efficiency of low power dc-dc converters regulated by digital voltage-mode PWM controllers. Depending on the input voltage, the controller adaptively changes the switching frequency, thus minimizing related losses while maintaining tight output voltage regulation and constraining electromagnetic interference (EMI) caused by the variable frequency operation. The presented architecture, whose key new element is alldigital adaptive clock and spread spectrum generator, can be implemented in the latest CMOS technologies and, as such, is well-suited for on-chip integration in portable battery-powered applications. The effectiveness of the system is verified with a 2.1 V/ 5 W buck prototype, where the input voltage ranges between 2.75 V and 5.5 V. The results show that, for an adaptive frequency regulation in the range between 780 kHz and 2 MHz, loss reduction of up to 18% is achieved.