PDA Hand-Held-Computer Power Controller

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The MAX781 is a system-engineered power-supply controller for subnotebook computers, PDAs, or similar battery-powered equipment. It provides high-performance, step-down (buck), pulse-width modulated (PWM) control for generating +3.3V and constant-current battery charging. Dual PCMCIA VPP outputs are powered by a regulated flyback winding. Five high-side gate drivers and a buffered analog multiplexer are also included. All functions are controlled by an SPI/Microwire™ compatible four-wire serial interface.

The MAX781 generates +3.3V with high efficiency through synchronous rectification and PWM operation at heavy loads. It uses Idle Mode™ operation at light loads. Only small external components are required because of the device's high switching frequency (300kHz) and advanced current-mode PWM architecture that allows for output capacitance as low as 50µF per ampere of load.

The MAX781 is configured by 32 bits of serial data. These bits select the operating mode, set the switch-mode battery charger current level, select one of eight analog multiplexer channels, and turn on/off the five high-side gate drivers. A status byte read from the serial interface indicates if the battery has been removed, if the DC charging source has been connected, or if there is a fault condition on the +3.3V output. An interrupt output signals the CPU if a status signal changes.

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