This paper presents the first-ever single-inductor programmable-output (SIPO) DC-DC Converters. A SIPO converter is comprised of a DC-DC converter and a Phase-locked Loop (PLL). Based on the input frequency generated internally, the PLL provides the reference voltage for the converter to generate the desired voltage levels. To demonstrate the SIPO design concept, a voltage-mode boost DC-DC converter with a constant duty-cycle pulse control technique is implemented. For an input voltage of 1.5V, the boost converter is programmed to boost the output voltages to 2V to 4V over 90% power efficiency for the load currents ranged from 50mA to 300mA.