DocID027438 Rev 1

7/13

AN4653

Cycling endurance

12

1.3

Cycling strategy

1.3.1

Cycling strategy and application temperature profile

In order to ensure the safest EEPROM cycling conditions, it is recommended to evaluate the

number of write cycles and the relative temperature profile of the cycling performed by the

EEPROM during the life of the application, that is:

Number of cycles at temp i

()

Max Number of cycles specified at temp i

()

------------------------------------------------------------------------------------

1

≤

i1

=

n

∑

•

define the main temperature ranges at which the EEPROM is operating in the end

application,

•

for each temperature range, estimate the number of write cycles executed for each

data block,

•

for each data block (with different cycling profiles), calculate the cumulated cycling

effect using the following equation or Table 3.

If the total percentage of cumulated cycles (last row in Table 3) is lower than 100%, the data

stored in the EEPROM are safely cycled.

If the total percentage of cumulated cycles is above 100%, the intrinsic safe margin for

cycling is exceeded and a data relocation strategy must be defined. This can be done by

distributing the number of cycles over several memory locations as follows:

•

define a cycling limit for each data block according to the application needs and product

performance (as shown in Table 3);

•

count the numbers of cycles executed on each data block (counter value can be stored

in the EEPROM);

•

when the counter exceeds the defined limit, the cycled data block must be relocated to

another physically independent memory address. The software developer should

define this new data block to be duplicated in a location inside a different page and,

when possible, not with the same byte address inside the new page. The counter itself

must also be stored in a new location.

1. The table can be adapted according to the temperature profile by taking care of putting down the maximum

cycling for each temperature.

Temperature

2. w and y are forecast number of cycles for a specific data block.

% of the max cycling value specified in Table 2

25°C

w

(w/4M) x 100 = a %

85°C

y

(y/1.2M) x 100 = b%

Total

w + y

(a + b) %