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DS1321 Datasheet

  • DS1321

  • Flexible Nonvolatile Controller with Lithium Battery Monitor

  • Dallas   Dallas

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DS1321
BATTERY VOLTAGE MONITORING
The DS1321 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 DS1321 connects V
BAT
to an internal 1 M鈩?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 DS1321 cannot constantly monitor an attached battery because such monitoring would
drastically reduce the life of the battery. As a result, the DS1321 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 DS1321 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 DS1321, 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 DS1321 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 DS1321
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 DS1321 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 defined by the TOL pin
(V
CCTP
), the V
CCI
comparator activates the reset signal
RST
. Reset occurs in the range of 4.75 to 4.5 volts
(5% tolerance) when the TOL pin is connected to GND or in the range of 4.5 to 4.25 volts (10%
tolerance) when TOL is connected to V
CCO
.
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.
RST
4 of 12

DS1321 產(chǎn)品屬性

  • Lead (SnPb) Finish for COTSObsolescence Mitigation Program

  • 25

  • 集成電路 (IC)

  • 存儲(chǔ)器 - 控制器

  • -

  • 非易失性 RAM

  • 4.75 V ~ 5.5 V

  • -40°C ~ 85°C

  • 16-DIP（0.300"，7.62mm）

  • 16-PDIP

  • 管件

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