The MAX1830/MAX1831 constant-off-time, pulse-widthmodulated (PWM) step-down DC-DC converters are ideal for use in 5V and 3.3V to low-voltage conversion necessary in notebook and subnotebook computers. These devices feature internal synchronous rectification for high efficiency and reduced component count. They require no external Schottky diode. The internal 45m PMOS power switch and 55m NMOS synchronous-rectifier switch easily deliver continuous load currents up to 3A. The MAX1830 produces preset +2.5V, +1.8V, or +1.5V output voltage or an adjustable output from +1.1V to VIN. The MAX1831 produces preset +3.3V, +2.5V, and +1.5V output voltages and an adjustable output from +1.1V to VIN. They achieve efficiencies as high as 94%. The MAX1830/MAX1831 use a unique current-mode, constant-off-time, PWM control scheme, which includes Idle ModeTM to maintain high efficiency during lightload operation. The programmable constant-off-time architecture sets switching frequencies up to 1MHz, allowing the user to optimize performance tradeoffs between efficiency, output switching noise, component size, and cost. Both devices are designed for continuous output currents up to 3A, an internal digital soft-start to limit surge currents during startup, a 100% duty cycle mode for low-dropout operation, and a low-power shutdown mode that disconnects the input from the output and reduces supply current below 1A.The MAX1830/MAX1831 are available in 16-pin QSOP packages.