DC-DC converter with digital adaptive slope control in auxiliary phase to achieve optimal transient response

In this paper, a new non-linear control scheme is presented to improve the dynamic response of a current-mode buck converter using a low-cost auxiliary phase. The problems associated with the existing solutions such as undesirable output voltage deviation and insufficient utilization of the auxiliary phase are addressed. This technique employs a digital adaptive slope control in the auxiliary phase, which can accommodate a range of auxiliary phase inductance values while maintaining optimal transient response. A calibration scheme is presented to calibrate the controller against variance in the main and auxiliary phase inductance. The control scheme is experimentally verified on a 500 kHz, 10 V to 2.5 V current-mode buck converter prototype. Charge balancing and optimal transient response are achieved for a range of both positive and negative load steps.