General Description 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 5.0V and 3.3V. These devices feature two linear 5V and 3.3V regulators to provide always-on outputs. Each linear regulator provides up to 100mA of output current. The linear regulators feature automatic steering to the main switching power supply output. The MAX1777/MAX1977/MAX1999 include on-board power-up sequencing, a power-good (PGOOD) output, digital soft-start, and internal soft-stop output discharge to prevent negative voltages during shutdown. Maxim's proprietary Quick-PWM™ fast-response, constant-on-time PWM control technique has no sense resistor and provides 100ns response to load transients while maintaining a relatively constant switching frequency. Unique ultrasonic pulse skipping maintains the mode switching frequency above 25kHz, thereby eliminating noise in audio applications. Other features include pulse skipping, which maximizes efficiency in light-load applications and fixed-frequency PWM mode, which reduces RFI-sensitive applications. The MAX1777 features a 200kHz/5V and 300kHz/3.3V switching power supply for the highest efficiency, while the MAX1977 features a 400kHz/5V and 500kHz/3.3V switching power supply for "slim and light" applications. The MAX1999 offers pin-selectable switching frequencies, allowing either 200kHz/300kHz or 400kHz/500kHz operation of 5V/3.3V SMPS, respectively. The MAX1777/MAX1977/MAX1999 are available in a 28-pin QSOP package and operate over the extended temperature range (-40°C to +85°C). The MAX1777/MAX1977/MAX1999 are lead-free packages.