DS1643-120 DALLAS [Dallas Semiconductor], DS1643-120 Datasheet - Page 5

• Manufacturer Part Number: DS1643-120
• Description: Nonvolatile Timekeeping RAM
• Manufacturer: DALLAS [Dallas Semiconductor]

DATA RETENTION MODE
When V
DS1643 can be accessed as described above by read
or write cycles. However, when V
er–fail point V
the internal clock registers and RAM is blocked from ac-
cess. This is accomplished internally by inhibiting ac-
cess via the CE and CE2 signals. When V
the level of the internal battery supply, power input is
switched from the V
clock activity, RAM, and clock data are maintained from
the battery until V
INTERNAL BATTERY LONGEVITY
The DS1643 has a self contained lithium power source
that is designed to provide energy for clock activity, and
CC
is within nominal limits (V
PF
(point at which write protection occurs)
CC
CC
is returned to nominal level.
pin to the internal battery and
CC
CC
is below the pow-
> 4.5 volts) the
CC
falls below
clock and RAM data retention when the V
not present. The capability of this internal power supply
is sufficient to power the DS1643 continuously for the
life of the equipment in which it is installed. For specifi-
cation purposes, the life expectancy is 10 years at 25 C
with the internal clock oscillator running in the absence
of V
Semiconductor with the clock oscillator turned off, so
the expected life should be considered to start from the
time the clock oscillator is first turned on. Actual life ex-
pectancy of the DS1643 will be much longer than 10
years since no internal lithium battery energy is con-
sumed when V
tions, the life expectancy of the DS1643 will be approxi-
mately equal to the shelf life (expected useful life of the
lithium battery with no load attached) of the lithium bat-
tery which may prove to be as long as 20 years.
CC
power. The DS1643 is shipped from Dallas
CC
is present. In fact, in most applica-
CC
041697 5/11
supply is
DS1643