A 25-MHz Four-Phase SAW Hysteretic Control DC-DC Converter With 1-Cycle Active Phase Count

In order to meet stringent power requirements in modern application processors, a 25-MHz four-phase dc-dc power converter is presented. It employs an adaptive window hysteretic control to facilitate ultra-fast transient response and minimize output voltage ( V_{O} ) undershoot and overshoot during load transient periods. Inherent clock synchronization ability ensures current balancing between phase sub-converters. The control also enables a wide range of programmable V_{O} for dynamic voltage/frequency scaling. To maintain high efficiency over a wide power range without degrading transient speed, a 1-cycle active phase count scheme is introduced. A design prototype was fabricated in a 0.35- \mu \text{m} CMOS process with an active die of 1.88 mm 2 . Simple circuit structure benefits a power density of 3.98 W/mm 2 . At a switching frequency of 25 MHz and a nominal input of 3.3 V, it regulates a programmable V_{O} ranging from 0.3 to 2.5 V. It achieves more than 80% efficiency over 96.7% of power range with a peak value of 88.1%. In response to 4-A load step-up/down, it achieves 103 mV/123 mV V_{O} undershoot/overshoot with 1% settling time of 190 ns/237 ns, respectively.