SINGLE_IC_BATTERY_BACUP_MANAGER

Published:2009/7/13 21:49:00 Author:May | From:SeekIC

Instruments powered by a wall adapter with battery backup typically diode-OR the battery and wall-adapter connections. That arrangement carries a penalty, however-the diode in series with the battery limits the minimum voltage at which the battery can supply power. One alternative is a dual-comparator/reference IC, which monitors the battery and wall-adapter voltages with respect to its internal reference voltage. The open-drain output of comparator B (with pull-up to 3.3 V) provides a low-battery warning in the form of a low-to-high transition when battery voltage drops to 3.6 V. The open-drain output of comparator A (with pull-up to 9 V) flags low wall-cube voltage in the same way, with a warning threshold of 3.9 V. Comparator A also controls the PMOS switch Q1, which replaces the OR-connection diode in a conventional circuit. When wall power is removed, Q1 turns on and provides a low-resistance path from battery to regulator.



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