The LM2608 step-down DC-DC converter is optimized for powering ultra-low voltage circuits from a single Lithium-Ion cell. It provides up to 400mA over an input voltage range of 2.8V to 5.5V. Operating from a 1.35V reference, this device provides pin-selectable output voltages of 1.3V/1.5V (300mA) for low voltage version or 1.5V/1.8V (400mA) for high voltage version. This allows adjustment for DSP or CPU voltage options, as well as dynamic output voltage switching for reduced power consumption. Internal synchronous rectification provides high efficiency. The LM2608 offers superior features and performance for mobile phones and similar portable applications with complex power management systems. Pin-selectable PWM lownoise and linear micropower modes offer improved system control for maximizing battery life. During full power operation, fixed-frequency PWM mode reduces interference in RF and data acquisition applications by minimizing noise harmonics at sensitive IF and sampling frequencies. A SYNC input allows synchronizing the switching frequency in a range of 500kHz to 1MHz to avoid noise from intermodulation with system frequencies. Linear operation reduces quiescent current to 20A (typ) during system standby for extended battery life. It provides up to 3 mA in the linear mode. Shutdown reduces battery consumption to 0.02A (typ.).