Datasheet

DS1314
3 of 12
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 DS1314 cannot constantly monitor an attached battery because such monitoring would
drastically reduce the life of the battery. As a result, the DS1314 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 DS1314 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 DS1314, 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 DS1314 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 DS1314
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
DS1314S and DS1314E varieties have an additional reset pin. These varieties detect out-of-tolerance
power supply conditions and warn a processor-based system of impending power failure. When V
CCI
falls
below the trip point level defined by the TOL pin (V
CCTP
), the V
CCI
comparator activates the reset signal
RST
. Reset occurs at 3.0V nominal (3.3V supply) when the TOL pin is connected to GND or at 2.7V
nominal (3.0V supply) when TOL is connected to V
CCO
.
RST
also serves as a power-on reset during power-up. After V
CCI
exceeds V
CCTP
,
RST
will be held active
for 200 ms 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 DS1314 without V
CC
power applied, the device does not
immediately provide battery-backup power on V
CCO
. Only after V
CCI
exceeds V
CCTP
and later falls below
both V
SW
and V
BAT
will the DS1314 leave Freshness Seal Mode and provide battery-backup power. This
mode allows a battery to be attached during manufacturing but not used until after the system has been
activated for the first time. As a result, no battery energy is drained during storage and shipping.