Current-mode variable-frequency control architecture for high-current low-voltage DC-DC converters

For controlling high-current low-voltage dc-dc converters, the control methods with variable switching frequency have the potential to achieve fast transient response and high efficiency. However, some issues in practical design limit the usefulness of the conventional variable-frequency control methods, such as the voltage-mode hysteretic control. This letter presents a novel implementation of current-mode variable-frequency control. The system architecture features a dual-loop feedback and a unique structure with symmetric signal paths for voltage and current signals. The symmetric structure provides practical advantages for integrated controller design to achieve accurate control on the droop resistance (or the load-line resistance). The system dynamics are analyzed with the small-signal model. Design guidelines are derived for simple compensation circuits to achieve constant output impedance. With variable switching frequency, the system achieves good dynamic response without requiring high switching frequency at steady-state. The system performance was verified by a two-channel interleaved controller chip implemented with CMOS technology.