Digital loss-minimizing multimode synchronous buck converter control

A multimode control strategy for a synchronous buck converter operating over a wide load range, is presented. For heavy loads, the converter runs in fixed-frequency continuous conduction mode (CCM). At light loads, it enters discontinuous conduction mode (DCM) with synchronous rectification. At still lighter loads, synchronous rectification is disabled in DCM. At very light loads, the converter operates in variable-frequency pulse skipping mode. The synchronous rectifier (SR) timing is scheduled as a function of the load current, enabling appropriate transition among the modes. An on-line adaptive algorithm to optimize the SR timing, based on power loss minimization, is presented. This control strategy is particularly well suited for a digital controller implementation, since it uses sophisticated computations, while not requiring high analog-to-digital conversion rates.