SS6550

SS6550 Low-Noise Synchronous PWM Step-Down DC/DC Converter n FEATURES l l l l n DESCRIPTION The SS6550 is a low-noise pulse-widthmodulated (PWM) DC/DC step-down converter, which can power logic circuits and transmitters in small wireless systems such as communicating PDAs, cellular phones and handy-terminals. The device features an internal synchronous rectifier for high conversion efficiency. Excellent noise characteristics and fixed-frequency operation provide easy post-filtering. The SS6550 is ideally suited for Li-Ion battery applications. It is also suitable for +3V or +5V fixed input applications. The device operates in one of the following four modes. Forced PWM mode operates at a fixed frequency regardless of the load. Synchronizable PWM mode allows the synchronization of an external switching frequency and minimizes harmonics. PWM/PFM Mode extends battery life by switching to a PFM pulse-skipping mode under light loads. Shutdown mode places the device in standby, reducing supply current to under 0.1µA. The SS6550 can deliver over 800mA of output current. The output voltage can be adjusted from 0.75V to VIN with the input range of +2.5V to +5.5V. Other features of the SS6550 include low quiescent current, low dropout voltage, and a ±1.2% accuracy 0.75V reference. It is available in a space-saving 8-pin MSOP package. L1 * 10µF R1 560K CF 15P + CO1 33µF CO2 4.7 µF VOUT = 1.8V l l l l l Greater than 95% efficiency. Guaranteed output current of 800mA. 100% duty cy...