MAX1844

MAX1844 19-1993; Rev 3; 9/02 EVAALVUAAILTAIOBNLEKIT High-Speed Step-Down Controller with Accurate Current Limit for Notebook Computers General Description The MAX1844 pulse-width modulation (PWM) controller provides high efficiency, excellent transient response, and high DC output accuracy needed for stepping down high-voltage batteries to generate low-voltage CPU core or chipset/RAM supplies in notebook computers. Maxim’s proprietary Quick-PWM™ quick-response, constant-on-time PWM control scheme handles wide input/output voltage ratios with ease and provides 100ns “instant-on” response to load transients while maintaining a relatively constant switching frequency. Efficiency is enhanced by an ability to drive very large synchronous-rectifier MOSFETs. Accurate current sensing to ensure reliable overload protection is available using an external current-sense resistor in series with the synchronous rectifier. Alternatively, the synchronous rectifier itself can be used for less accurate current sensing at the lowest possible power dissipation. Single-stage buck conversion allows the MAX1844 to directly step down high-voltage batteries for the highest possible efficiency. Alternatively, two-stage conversion (stepping down the 5V system supply instead of the battery) at a higher switching frequency allows the minimum possible physical size. The MAX1844 is intended for CPU core, chipset, DRAM, or other low-voltage supplies as low as 1V. It is available in 20-pin QSOP, and QFN pa...