© 1992 Microchip Technology Inc.

DS00537A-page 7

8

Serial EEPROM Endurance

FIGURE 6 - EXAMPLE #1: THE AUTOMOBILE COMPASS

EXAMPLE #1 - AUTOMOBILE

ELECTRONIC COMPASS

A 16-byte (128-bits) segment from a 2K array stores

data every time the power is turned off in an automobile

electronic compass. The design engineers expect the

system to power down an average of 5 times/day over a

10-year life in an 85

°C case temperature environment.

The projected Microchip cumulative failure rate under

these conditions at the 10 year point is less than 8 PPM

or 0.0008% failures in 10 years. The cumulative PPM

failure rate graph is referenced on Figure 6.

EXAMPLE #2 FULL-FEATURED

TELEPHONE

An 8-byte (64-bit) segment is used to store the last

number redial on a stationary full feature phone operat-

ing in a room temperature environment. A 12K bit

(12,288-bits) segment is used for storage of speed dial

numbers on the same phone. This application has two

major functions and therefore it will have two separate

failure rate calculations.

The last number redial function is expected to be utilized

an average of 20 times/day over a 10 year life. Each

speed dial is expected to be updated an average of 0.1

times/day over a 10 year life.

Figure 7, the cumulative failure rate graph for these two

conditions indicates an extremely low failure rate in the

projected 10 year lifetime. The failure rate begins be-

yond 20 years as shown on the attached cumulative

PPM failure rate graph.

EXAMPLE #3 - LASER PRINTER

A serial EEPROM could have many functions in a laser

printer. A function that would likely require the most

cycles/day is the maintenance log storage of the pages

printed (estimated to be 100 cycles/day). Three bytes

are utilized to store this number. The case temperature

environment is estimated to be between 55

°C and 85°C

The high number of cycles at an extreme temperature of

85

°C indicate a failure rate of less than 1200 PPM

through the first 5 years and 2600 PPM through the first

10 years.

This failure rate can be dramatically reduced if the

operating temperature is reduced to 55

°C. The same 5

and 10 year PPM levels are reduced to 450 PPM and

1600 PPM at 55

°C.

These failure rates are illustrated on Figure 8.

SUMMARY

Microchip Technology Inc. has recognized that increas-

ing reliability in serial EEPROMs through increased

endurance is not a function of extending the life of the

intrinsic erase/write cycle, but depends on reducing

defect-density failure rates. Design engineers charac-

terizing EEPROM memory needs for an application and

evaluating EEPROM components from various manu-

facturers need to understand not only the relationship

between the application and expected use and failure

mechanisms, but also how the manufacturer has arrived

at published endurance data for its components.

24LC02, 85C, 5V, 16bytes, 5cycles/day, RANDOM, BYTE

,

18,250 Cycles,

10.0 Yrs

PPM = 82

0

20

40

60

80

100

0.000

0.005

0.010

0.015

0.020

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