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This paper reports a delay-locked loop (DLL) based hysteretic controller for high-frequency multiphase dc-dc buck converters. The DLL control loop employs the switching frequency of a hysteretic comparator as reference to automatically synchronize the remaining phases and eliminate the need for external synchronization. A dedicated duty cycle control loop is used to enable current sharing and ripple cancellation. We demonstrate a four-phase high-frequency buck converter that operates at 25-70 MHz with fast hysteretic control and output conversion range of 17.5%-80%. The converter achieves an efficiency of 83% at 2 W and 80% at 3.3 W. The circuit has been implemented in standard 0.5 mum 5 V CMOS process.
Date of Publication: Nov. 2009