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Description
The DS1323 flexible nonvolatile controller with lithium battery monitor is a CMOS circuit that solves the application problem of converting CMOS SRAMs into nonvolatile memory. Incoming power
is monitored for an out-of-tolerance condition. When such a condition is detected, chip enable outputs are inhibited to accomplish write protection and the battery is switched on to supply the SRAMs with uninterrupted power. Special circuitry uses a low-leakage CMOS process that affords precise voltage detection at extremely low-battery consumption. One DS1323 can support as many as four SRAMs arranged in any of three memory configurations.
In addition to battery-backup support, the DS1323 performs the important function of monitoring the remaining capacity of the lithium battery and providing a warning before the battery reaches end-of-life. Because the open-circuit voltage of a lithium backup battery remains relatively constant over the majority of its life, accurate battery monitoring requires loaded-battery voltage measurement. The DS1323 performs such measurement by periodically comparing the voltage of the battery as it supports an internal resistive load with a carefully selected reference voltage. If the battery voltage falls below the reference voltage under such conditions, the battery will soon reach end-of-life. As a result, the Battery Warning pin is activated to signal the need for battery replacement.
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