A 90–240MHz hysteretic controlled DC-DC buck converter with digital PLL frequency locking

This paper reports a digital phase locked loop (DPLL) frequency locking technique for high frequency hysteretic controlled dc-dc buck converters. The proposed technique achieves constant operating frequency over a wide output voltage range, eliminating the dependence of switching frequency on duty cycle or output voltage conversion range. The DPLL is programmable over a wide range of parameters and can be locked to a reference clock to ensure the converter switching frequency falls outside power supply resonance bands. We demonstrate a 90-240 MHz single phase converter with fast hysteretic control and output conversion range of 33%-80%. The converter achieves an efficiency of 80% at 180 MHz, a load response of 40 ns for a 120 mA current step and a peak-to-peak ripple less than 25 mV. The circuit was implemented in 130 nm digital CMOS process.