The LM2640 is a dual step-down power supply controller intended for application in notebook personal computers and other battery-powered equipment. Fixed-frequency synchronous drive of logic-level N-channel power MOSFETs is combined with an optional pulse-skipping mode to achieve ultra efficient power conversion over a 1000:1 load current range. The pulse-skipping mode can be disabled in favor of fixed-frequency operation regardless of the load current level. High DC gain and current-mode feedback control assure excellent line and load regulation and a wide loop bandwidth for fast response to dynamic loads. An internal oscillator fixes the switching frequency at 200 kHz. Optionally, switching can be synchronized to an external clock running as fast as 400 kHz. An optional soft-start feature limits current surges from the input power supply at start up and provides a simple means of start-up sequencing. Logic-level inputs allow the controllers to be turned ON and OFF separately.