Power Source Selector for Dual-Battery Systems

The MAX1773/MAX1773A highly integrated ICs serve as the control logic for a system with multiple power sources. They directly drive external P-channel MOSFETs to select from an AC adapter and dual battery sources for charge and discharge. The selection is made based on the presence of the power sources and the state of the batteries. The MAX1773/MAX1773A detect low battery conditions using integrated analog comparators and check for the presence of a battery by using battery thermistor outputs.

The MAX1773/MAX1773A are designed for use with a buck topology charger. They provide a simple and easily controlled solution to a difficult analog power control problem. The MAX1773/MAX1773A provide most of the power source monitoring and selection, freeing the system power management microprocessor (µP) for other tasks. This not only simplifies development of the power management firmware for the µP but also allows the µP to enter standby, thereby reducing system power consumption.

The MAX1773A is recommended for new designs.

Applications

* Dual-Battery Portable Equipment * Internet Tablets * Notebook and Subnotebook Computers * PDAs and Handy-Terminals

* 7-MOSFET Topology Offers Low-Cost Solution

* Automatically Detects and Responds to:

* Low Battery Voltage Condition

* Battery Insertion and Removal

* AC Adapter Presence

* Direct Drive of P-Channel MOSFETs

* Simplifies Power Management µP Firmware

* Extends Battery Life by Allowing Power Management µP to Enter Standby

* 4.75V to 28V AC Adapter Input Voltage Range

* Integrated LDO with 1mA Drive Capability

* Small Footprint 20-Pin TSSOP Package