100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter

The MAX887 high-efficiency, step-down DC-DC converter provides an adjustable output from 1.25V to 10.5V. It accepts inputs from 3.5V to 11V and delivers 600mA. Operation to 100% duty cycle minimizes dropout voltage (300mV typ at 500mA). Synchronous rectification reduces output rectifier losses, resulting in efficiency as high as 95%.

Fixed-frequency pulse-width modulation (PWM) reduces noise in sensitive communications applications. Using a high-frequency internal oscillator allows tiny surface-mount components to reduce PC board area, and eliminates audio-frequency interference. A SYNC input allows synchronization to an external clock to avoid interference with sensitive RF and data-acquisition circuits.

The MAX887 features current-mode operation for superior load/line-transient response. Cycle-by-cycle current limiting protects the internal MOSFET and rectifier. A low-current (2.5µA typ) shutdown mode conserves battery life.

Applications

* Cell Phones * Computer Peripherals * Distributed Power Systems * Personal Communicators * Portable Instrumentation

* 95% Efficiency

* 600mA Output Current

* Cycle-by-Cycle Current Limiting

* Low-Dropout, 100% Duty-Cycle Operation, 300mV at 500mA

* Internal 0.6Ω (typ) MOSFET

* Internal Synchronous Rectifier

* High-Frequency Current-Mode PWM

* External SYNC or Internal 300kHz Oscillator

* Guaranteed 260kHz to 340kHz Internal Oscillator Frequency Limits

* 2.5µA Shutdown Mode