Step-Up Converter Designed For Pagers

A high-efficiency, low-voltage, synchronous-rectified, step-up dc-to-dc converter is designed to be powered by one to three alkaline, NiCad or NiMH cells or one lithium cell. The MAX1678 converter is guaranteed to start-up at 0.87V; quiescent current is 37 µA (2 µA in shutdown). An internal synchronous rectifier eliminates the need for an external Schottky diode and boosts efficiency to 90% while providing more than 50 mA of output current from one cell. More than 90 mA is available from a two-cell supply. Output voltage is preset at 3.3V or can be adjusted from 2V to 5.5V using two external resistors.