The MAX1777/MAX1977/MAX1999 dual step-down, switch-mode power-supply (SMPS) controllers generate logic-supply voltages in battery-powered systems. The MAX1777/MAX1977/MAX1999 include two pulse-width modulation (PWM) controllers, adjustable from 2V to 5.5V or fixed at 5V and 3.3V. These devices feature two linear regulators providing 5V and 3.3V always-on outputs. Each linear regulator provides up to 100mA output current with automatic linear regulator bootstrapping to the main SMPS outputs. The MAX1777/MAX1977/MAX1999 include on-board power-up sequencing, a power-good (PGOOD) output, digital soft-start, and internal soft-stop output discharge that prevents negative voltages on shutdown. Maxim's proprietary Quick-PWMTM quick-response, constant on-time PWM control scheme operates without sense resistors and provides 100ns response to load transients while maintaining a relatively constant switching frequency. The unique ultrasonic pulse-skipping mode maintains the switching frequency above 25kHz, which eliminates noise in audio applications. Other features include pulse skipping, which maximizes efficiency in light-load applications, and fixed-frequency PWM mode, which reduces RF interference in sensitive applications. The MAX1777 features a 200kHz/5V and 300kHz/3.3V SMPS for highest efficiency, while the MAX1977 features a 400kHz/5V and 500kHz/3.3V SMPS for "thin and light" applications. The MAX1999 provides a pin-selectable switching frequency, allowing either 200kHz/300kHz or 400kHz/500kHz operation of the 5V/3.3V SMPSs, respectively. The MAX1777/MAX1977/MAX1999 are available in 28-pin QSOP packages and operate over the extended temperature range (-40C to +85C).