The MAX1533/MAX1537 are dual step-down, switch-mode power-supply (SMPS) controllers with synchronous rectification, intended for main 5V/3.3V power generation in battery-powered systems. Fixed-frequency operation with optimal interleaving minimizes input ripple current from the lowest input voltages up to the 26V maximum input. Optimal 40/60 interleaving allows the input voltage to go down to 8.3V before duty-cycle overlap occurs, compared to 180° out-of-phase regulators where the duty-cycle overlap occurs when the input drops below 10V. Output current sensing provides accurate current limit using a sense resistor. Alternatively, power dissipation can be reduced using lossless inductor current sensing. Internal 5V and 3.3V linear regulators power the MAX1533/MAX1537 and their gate drivers, as well as external keep-alive loads, up to a total of 100mA. When the main PWM regulators are in regulation, automatic bootstrap switches bypass the internal linear regulators, providing currents up to 200mA from each linear output. An additional 5V to 23V adjustable internal 150mA linear regulator is typically used with a secondary winding to provide a 12V supply. The MAX1533/MAX1537 include on-board power-up sequencing, a power-good (PGOOD) output, digital soft-start, and internal soft-shutdown output discharge that prevents negative voltages on shutdown. The MAX1533 is available in a 32-pin 5mm x 5mm thin QFN package, and the MAX1537 is available in a 36-pin 6mm x 6mm thin QFN package. The exposed backside pad improves thermal characteristics for demanding linear keep-alive applications. Applications * 2 to 4 Li+ Cell Battery-Powered Devices * Notebook and Subnotebook Computers * PDAs and Mobile Communicators