DS1644LPM

041697 5/11

DATA RETENTION MODE

DS1644L can be accessed as described above with

curs) the internal clock registers and RAM are blocked

from access. This is accomplished internally by inhibit-

ing access via the CE signal. At this time the power–fail

output signal (PFO) will be driven active low and will

battery and clock activity, RAM, and clock data are

nominal level.

INTERNAL BATTERY LONGEVITY

The DS1644L has a self contained lithium power source

that is designed to provide energy for clock activity, and

not present. The capability of this internal power supply

is sufficient to power the DS1644L 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

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 DS1644L will be much longer than 10

years since no internal lithium battery energy is con-

tions, the life expectancy of the DS1644L will be approx-

imately 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.