CCM/GM Relative Skip Energy Control and Bidirectional Dynamic Slope Compensation in a Single-Inductor Multiple-Output DC-DC Converter for Wearable Device Power Solution

Abstract

Compact size wearable devices require multiple supplies with relative large loading difference, which causes serious cross regulation, large ripple, and oscillation in single-inductor multiple-output (SIMO) DC-DC converter. Thus, a continuous conduction mode/green mode (CCM/GM) relative skip energy control (RSEC) in SIMO is proposed for wearable device power solution. Different from the conventional absolute skip method, the RSEC eliminates unnecessary skip-induced voltage ripple and cross regulation with well regulation performance over wide load and voltage ranges. Optimization between efficiency and voltage ripple achieves low noise supply and reduced switching loss. In addition, smooth transition between CCM and GM provides high power and longer usage time in wearable devices. Furthermore, bidirectional dynamic slope compensation conquers subharmonic oscillation and avoids invalid pulses in the energy delivery operation of current-mode SIMO DC-DC converters. The test chip fabricated in the 0.18 mu m CMOS process occupies 2.24 mm(2) active area. Maximum output ripple, overshoot/undershoot, and cross regulation are kept below 40 mV, 27 mV, and 0.0432 mV/mA, respectively.