A 5 MHz High-Speed Saturating Inductor DC-DC Converter Using Cycle-by-Cycle Digital Control

The fastest transient response of dc-dc converters, which is a dominant performance criterion for dynamic voltage scaling (DVS), is fundamentally limited by the inductor current slew rate. We employ a saturating inductor with a systematic control design to increase the slew rate without introducing extra hardware. The resulting 5 MHz saturating inductor current-mode buck converter using constant-on-time (CM-COT buck converter) controlled by a high-speed cycle-by-cycle digital controller that is designed under the switching-synchronized sampled-state space (5S) control framework exhibits a 2.6 μs large-signal voltage risetime (10%-90%) with no overshoot. Furthermore, we extend the 5S control framework to this nonlinear converter plant by utilizing singular perturbation theory. The resulting controller exhibits a large-signal stability and an ability to handle a peak slew current that is 11 times the steady-state average current in a 30 W saturating inductor CM-COT buck converter prototype.