DPWM time resolution requirements for digitally controlled DC-DC converters

Digitally controlled dc-dc converters can exhibit undesired limit-cycle oscillations due to the lack of time resolution in the digital pulse-width modulator (DPWM) to satisfy specified output voltage regulation accuracy. In this paper, the relationship between DPWM time resolution and output voltage regulation accuracy is studied for several basic converters operating in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM). The minimum DPWM time resolution required to prevent limit-cycle oscillations is then derived cycle-skip, a technique for adjusting the switching frequency and on-time without load current sensing, is proposed to improve the output voltage regulation accuracy and lower DPWM resolution requirements. Experimental results are provided to validate the theoretical analysis and the effectiveness of the cycle-skip technique in avoiding limit-cycle oscillations.