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DS1312

Nonvolatile Controller with Lithium Battery Monitor

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DS1312

Nonvolatile Controller with Lithium

Battery Monitor

FEATURES

z Converts CMOS SRAM into nonvolatile memory

z Unconditionally write-protects SRAM when Vcc is out of

tolerance

z Automatically switches to battery backup supply when Vcc

power failure occurs

z Monitors voltage of a lithium cell and provides advanced

warning of impending battery failure

z Signals low-battery condition on active low battery Warning

output signal

z Optional 5% or 10% power-fail detection

z Space-saving 8-pin DIP and SOIC packages

z Optional 16-pin SOIC and 20-pin TSSOP versions reset

process or when power failure occurs and hold processor in

reset during system power-up

z Industrial temperature range of -40℃ to +85℃

PIN ASSIGNMENT

PIN DESCRIPTION

VCCI

VCCO

VBAT

-+5V Power Supply Input

-SRAM Power Supply Output

-Backup Battery Input

-Chip Enable Input

-Chip Enable Output

TOL

-Vcc tolerance Select

-Battery Warning Output (Open Drain)

-Reset Output (Open Drain)

GND

-Ground

NC

-No Connection

DESCRIPTION

The DS1312 Nonvalatile Controller with Battery Monitor is a CMOS circuit which solves the application problem of converting

CMOS RAM into nonvolatile memory. Incoming power is monitored for an out-of-tolerance condition. When such a condition is

detected, chip enable is inhibited to accomplish write protection and the battery is switched on to supply the RAM with

uninterrupted power. Special circuitry uses a low-leakage CMOS process which affords precise voltage detection at extremely low

battery consumption.

In addition to battery-backup support, the DS1312 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 DS1312 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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