Controller scalability methods for digital Point Of Load converters

Unmodeled dynamics cause DC-DC controller design to be an iterative procedure where controller parameters are tuned and re-tuned to achieve the desired transient performance. Once the controller is designed any change of the output filter requires a new compensator design to guarantee stable operation. In this paper programmability of controller parameters in digital Point Of Load (POL) converters is exploited to investigate methods to scale an existing controller to accommodate variation of the resonant frequency of the LC filter, with the aim to eliminate the need for such iterative tuning. A new method to scale a compensator is then proposed to maintain bandwidth and phase margin of the original controller design. Experimental results are provided for 12-to-1.2V, 20A, 500kHz 0.18μm CMOS digital POL converter to show the effectiveness of the proposed method.