This paper introduces an approach to near timeoptimal control for synchronous buck dc-dc converters. The proposed proximate time-optimal digital (PTOD) controller is a combination of a constant-frequency pulsewidth modulation (PWM) controller employing a linear PID compensator close to a reference point, and a linear or nonlinear switching surface controller (SSC) away from the reference, together with smooth transitions between the two. A hybrid capacitor current estimator enables switching surface evaluation and eliminates the need for current sensing. The SSC, which is implemented as a small Verilog HDL module, can be easily added to an existing digital PWM controller to construct the PTOD controller. In steady state, the controller operates exactly the same as a standard constant-frequency PWM controller with a linear PID compensator. Simulation and experimental results are shown for a 6.5 V-to-1.3 V, 10 A synchronous buck converter.

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