Frequency-Linked Power-MOSFET Segmentation for Efficiency Optimization in a DC-DC Buck Converter for Application Processors

Modern application processors (APs) demand an efficient power management solution to prolong the battery life without compromising the transient performance. To meet these stringent requirements, we propose a frequency-linked power-MOSFET segmentation in a current-mode DC-DC buck converter, specifically enhancing low-load efficiency. While load- driven power-MOSFET segmentation is well-known, the present work proposes the frequency-linked power MOSFET segmentation, wherein discretely adjusting the switching frequency along with power-MOSFET segmentation to further minimize the losses and enhance the low load efficiency ensuring less efficiency variation across the load range. Furthermore, the addition of the auxiliary phase during transients helps to achieve a fast transient response. The proposed converter is designed using a 180-nm CMOS process for an input voltage range of 2.5-3.3 V with an output voltage of 1.2 V and it operates at a switching frequency of either 5 MHz or 10 MHz. The proposed design achieves a power efficiency greater than 90% in the entire range of 0.1-1 A with an improvement of ~ 5 % at light load conditions. During transients, it shows a very fast settling response of 360/410 ns with an undershoot/overshoot of 27/20 mV for a load current slew rate of 1.5 A/ns.