Stability Boundaries of Wide-Input-Range COT Buck Converters With Ripple Compensation

In this paper, we focus on instability issues of a wide-input-range Constant ON-Time buck converter. A transconductance stage in the control path that implements ripple compensation characterizes the architecture of this switching circuit. On the whole, decision rules, that heavily influence stability, govern the dynamical evolution of the converter. We show the onset of sub-harmonic oscillations and pulse-bursting caused by the presence of hysteresis in the regulation comparator. Operational boundaries are provided both in analytical and numerical form. They easily support the designer in choosing the converter parameter values. Theoretical results are verified against SIMetrix/SIMPLIS and MPLAB® Mindi™ simulations for a case study involving a commercial adjustable-frequency, synchronous buck regulator featuring an adaptive ON-time control architecture. A good agreement is obtained, as shown.