This paper presents a single-inductor triple-output (SITO) buck-boost converter for wearable devices. It converts a 2.8V to 4.8V Li-ion battery voltage to three regulated output voltages: 1.2 V, 1.8V, and 3.3V for different back-end circuits, such as digital circuits and analog circuits. In order to reduce the cross regulation issue, the converter operates at discontinuous conduction mode (DCM) and regulates the output using pulse-skip modulation (PSM). The converter includes an adaptive on-time (AOT) generator to improve the output power range at low input voltage and to control the maximum output voltage ripple under different input. Three self-tracking zero current detectors (ST-ZCD) provides appropriate off-time periods for power MOSFETs to reduce the reverse inductor current. Furthermore, the input voltage shorts to the third output to extend the battery life. The measurement results show that the proposed SITO buck-boost converter achieves a maximum peak power conversion efficiency of 75.8% under 315mW output power. The peak inductor current is well controlled under different input voltages.