Chip Generates Main Supply For PDAs Or Handheld GPS Units

The MAX1677 is a dual-output, step-up dc-to-dc converter that delivers a 3.3V or adjustable (2.5V to 5.5V) main output at up to 350 mA and an adjustable secondary output of up to +28V or -28V for LCD bias from one- or two-cell battery inputs. The device is suited for use in PDAs, GPS receivers, and other handheld, battery-powered systems.No external FET is required by the device, which uses an internal synchronous rectifier to eliminate a Schottky diode and to boost efficiency to as high as 95%. Users can choose from two operating modes: a 300-kHz fixed frequency PWM mode for lowest noise in wireless applications; or a low-current PFM mode, in which the device's quiescent current is a low 30 µA for maximum battery life. Logic-level shutdown controls allow the LCD regulator to be shut down independently from the main supply.