10.7 A 25MHz 4-phase SAW hysteretic DC-DC converter with 1-cycle APC achieving 190ns tsettle to 4A load transient and above 80% efficiency in 96.7% of the power range

Switching power converters with fast load transients are crucial for application processors (APs) to facilitate system-level power adaptability with high current slew rate. While current-mode hysteretic control has been popularly employed in switching converters for simple structure, robust operation and fast transient response [1], it still does not suffice for the unprecedented 1A/ns current slew rate required by modern APs [2]. Meanwhile, current slew rate can be improved by extending single-phase to multiphase operation. However, when a converter powers light load, power loss caused by added phases adversely affects the efficiency. Active phase count (APC) was thus proposed to manage the number of active phases judiciously to load by sensing average inductor current [3,4]. However, the inherent sensing delay drastically slows down the phase adding/dropping actions and degrades load transient response. On the other hand, phase current imbalance among phase sub-converters could cause hot spots, jeopardizing system reliability. Upgrading from conventional current-mode hysteretic control, we propose a simple synchronized adaptive window (SAW) hysteretic control which automatically adjusts the hysteretic window to speed up the transient response. Inherent clock synchronization makes it a natural fit to multiphase operation, where APC can be accomplished within one switching cycle through an internal current sensing mechanism in the control.