The MAX1549 dual pulse-width modulation (PWM) stepdown controller provides the high efficiency, excellent transient response, and high DC-output accuracy necessary for generating low-voltage chipset and RAM power supplies in notebook computers. The controller employs a fixed-frequency, current-mode PWM architecture that does not require complex compensation. The MAX1549 also interleaves the dual step-down regulators, minimizing the input capacitor requirements. The MAX1549 features differential current-sense inputs for accurately sensing the inductor current across an external current-sense resistor in series with the output to ensure reliable overload protection. Alternatively, the controller can provide overload protection using lossless inductor current-sensing methods, lowering power dissipation and reducing system cost. Single-stage buck conversion allows the MAX1549 to directly step down high-voltage batteries for the highest possible efficiency. Very low output-voltage applications require two-stage conversion--stepping down from another system supply rail instead of the battery. The MAX1549 powers chipsets and graphics processor cores that require dynamically adjustable output voltages, or generates the active termination bus that must track the input reference. The main step-down controller (OUT1) regulates the dedicated reference input (REFIN) voltage generated by a resistive voltage-divider from the MAX1549's reference. The MAX1549 also includes internal open-drain pulldowns with logic-level control inputs to dynamically adjust the REFIN resistive-divider ratio. When a transition occurs on these control inputs, the controller enters forced-PWM mode and blanks the power-good (PGOOD1) output and output fault protection. OUT2 uses a Dual-ModeTM feedback input to provide either fixed 2.5V/1.8V or adjustable output voltage regulation. The MAX1549 is available in a 40-pin, 6mm x 6mm thin QFN package.