DS1323_1205 Datasheet, PDF (4/14 Pages) Maxim Integrated Products – 3.3V Flexible Nonvolatile Controller with Lithium Battery Monitor

DS1323
BATTERY VOLTAGE MONITORING
The DS1323 automatically performs periodic battery voltage monitoring at a factory-programmed time
interval of 24 hours. Such monitoring begins within t_REC after V_CCI rises above V_CCTP and is suspended when
power failure occurs.
After each 24-hour period (t_BTCN) has elapsed, the DS1323 connects V_BAT to an internal 1MΩ test resistor
(R_INT) for one second (t_BTPW). During this one second, if V_BAT falls below the factory-programmed battery
voltage trip point (V_BTP), the battery warning output BW is asserted. While BW is active, battery testing will
be performed with period t_BTCW to detect battery removal and replacement. Once asserted, BW remains
active until the battery is physically removed and replaced by a fresh cell. The battery is still retested after
each V_CC power-up, however, even if BW was active on power-down. If the battery is found to be higher
than V_BTP during such testing, BW is deasserted and regular 24-hour testing resumes. BW has an open-drain
output driver.
Battery replacement following BW activation is normally done with V_CCI nominal so that SRAM data is not
lost. During battery replacement, the minimum time duration between old battery detachment and new
battery attachment (t_BDBA) must be met or BW will not deactivate following attachment of the new battery.
Should BW not deactivate for this reason, the new battery can be detached for t_BDBA and then re-attached to
clear BW .
NOTE: The DS1323 cannot constantly monitor an attached battery because such monitoring would
drastically reduce the life of the battery. As a result, the DS1323 only tests the battery for one second out of
every 24 hours and does not monitor the battery in any way between tests. If a good battery (one that has not
been previously flagged with BW ) is removed between battery tests, the DS1323 may not immediately sense
the removal and may not activate BW until the next scheduled battery test. If a battery is then reattached to
the DS1323, the battery may not be tested until the next scheduled test.
NOTE: Battery monitoring is only a useful technique when testing can be done regularly over the entire life
of a lithium battery. Because the DS1323 only performs battery monitoring when V_CC is nominal, systems
which are powered down for excessively long periods can completely drain their lithium cells without
receiving any advanced warning. To prevent such an occurrence, systems using the DS1323 battery
monitoring feature should be powered up periodically (at least once every few months) in order to perform
battery testing. Furthermore, anytime BW is activated on the first battery test after a power-up, data integrity
should be checked via checksum or other technique.
POWER MONITORING
The DS1323 automatically detects out-of-tolerance power supply conditions and warns a processor-based
system of impending power failure. When V_CCI falls below the trip point level in the range of 3.0 to 2.8 volts
(10% tolerance) (V_CCTP), the V_CCI comparator activates the reset signal RST .
RST also serves as a power-on reset during power-up. After V_CCI exceeds V_CCTP, RST will be held active
for 200ms nominal (t_RPU). This reset period is sufficiently long to prevent system operation during power-on
transients and to allow t_REC to expire. RST has an open-drain output driver.
FRESHNESS SEAL MODE
When the battery is first attached to the DS1323 without V_CC power applied, the device does not
immediately provide battery-backup power on V_CCO. Only after V_CCI exceeds V_CCTP will the DS1323 leave
Freshness Seal Mode. This mode allows a battery to be attached during manufacturing but not used until
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