This letter presents a boost-oriented single-inductor dual-output (BO-SIDO) step-up/down dc–dc converter. The BO-SIDO design enables only 1×RON conduction in all inductor-current paths, improving power efficiency. While regulating the heavy-loaded boost output, the buck conversion can be embedded adaptively to the buck load. The chip able to power one boost and one buck output was fabricated in 0.5- μm CMOS, and it achieved 96.6% peak efficiency and a maximum output power of 5.6 W.