M48T08-100PC View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

M48T08-100PC

CMOS 8K x 8 TIMEKEEPER SRAM

STMicroelectronics 

M48Z08, M48Z18

Cell Storage Life

Storage life is primarily a function of temperature.

Figure 9 illustrates the approximate storage life of

the M48Z08,18 battery over temperature. The re-

sults in Figure 9 are derived from temperature

accelerated life test studies performed at SGS-

THOMSON. For the purpose of the testing, a cell

failure is defined as the inability of a cell stabilized

at 25°C to produce a 2.4V closed circuit voltage

across a 250 kΩ load resistor. The two lines, t1%

and t50%, represent different failure rate distribu-

tions for the cell’s storage life. At 70°C, for example,

the t1% line indicates that an M48Z08,18 has a 1%

chance of having a battery failure 28 years into its

life while the t50% shows the part has a 50% chance

of failure at the 50 year mark. The t1% line repre-

sents the practical onset of wear out and can be

considered the worst case Storage Life for the cell.

The t50% can be considered the normal or average

life.

Calculating Storage Life

The following formula can be used to predict stor-

age life:

1

{[(TA1/TT)/SL1]+[(TA2/TT)/SL2]+...+[(T AN/TT)/SLN]}

where,

– TA1, TA2, TAN = time at ambient temperature

1, 2, etc.

– TT = total time = TA1+TA2+...+TAN

– SL1, SL2, SLN = storage life at temperature 1,

2, etc.

For example an M48Z08,18is exposed to tempera-

tures of 55°C or less for 8322 hrs/yr, and tempera-

tures greater than 60°C but less than 70°C for the

remaining 438 hrs/yr. Reading predicted t1% values

from Figure 9,

– SL1 ≅ 200 yrs, SL2 = 28 yrs

– TT = 8760 hrs/yr

– TA1 = 8322 hrs/yr, TA2 = 438 hrs/yr

Predicted storage life ≥

1

{[(8322/8760)/200]+[(431/8760)/28]}

or 154 years.

As can been seen from these calculations and the

results, the expected lifetime of the M48Z08, 18

should exced most system requirements.

Estimated System Life

Since either storage life or capacity consumption

can end the battery’s life, the system life is marked

by which ever occurs first.

Reference for System Life

Each M48Z08,18 is marked with a nine digit manu-

facturing date code in the form of H99XXYYZZ. For

example, H995B9431 is:

H = fabricated in Carrollton, TX

9 = assembled in Muar, Malaysia,

9 = tested in Muar, Malaysia,

5B = lot designator,

9431 = assembled in the year 1994, work week 31.

10/15

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