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In this paper, a sub-1 V input single-inductor dual-output (SIDO) dc-dc converter with an adaptive load-tracking control (ALTC) technology is proposed for single-cell-powered portable devices. Having a minimal number of switches and an optimum current sequence, the proposed ALTC technique adaptively and accurately adjusts storage energy in the form of inductor current according to the actual load condition, without wasting surplus charge and without increasing cross regulation. Moreover, a current-mode ring oscillator with a self-bias current source circuit, in place of the conventional start-up ring oscillator, is proposed to produce a nearly constant system clock for the requirement of sub-1 V start-up procedure. Because the proposed current-mode ring oscillator operates between the start-up process and steady state of the SIDO dc-dc converter, its simplified design efficiently addresses the high switching frequency losses at sub-1 V start-up procedure, reducing chip area and power consumption. The proposed sub-1 V input SIDO dc-dc converter was fabricated via Taiwan Semiconductor Manufacturing Company 0.25 μm 2.5 V/5 V Bipolar-CMOS-DMOS process, and the experimental results show high efficiency of 92% with a good cross regulation smaller than 10 mV.