AN1836 Motorola / Freescale Semiconductor, AN1836 Datasheet - Page 28

• Manufacturer Part Number: AN1836
• Description: FLASH Programming for Motorola MC68HC912 Microcontrollers
• Manufacturer: Motorola / Freescale Semiconductor

Application Note
FLASH Lifetime
Effects of Age
on FLASH Array
Possible Failure
Mechanisms
28
covered are the lifetime of the FLASH memory itself and the effects of
age and usage on the FLASH array. Also important to discuss are the
failure mechanisms involved when V
testing for marginally programmed memories.
The main purpose of NVM is long-term storage of programs and data.
As a result, it is of prime concern to the application designer to know how
long that information will be stored correctly. Motorola guarantees a
FLASH data retention lifetime of 10 years for properly programmed data,
based on an average operating temperature of 70
Since FLASH EEPROM is also electrically erasable, it is ideally suited
for in-circuit updating and rapid code modifications. The memory does,
however, have a finite number of program and erase cycles it can be put
through before it fails. Motorola guarantees 100 program/erase cycles
on the MC68HC912B32 device, which is based on 125 C.
As the FLASH memory’s bitcells are written and erased over many
cycles, they tend to "age." The primary effect is that over time, gradually,
more and more erase or programming pulses are required to erase or
program the bitcell. This has been taken into account in the algorithms
for programming and erasing. The algorithms ensure that only the
fewest number of pulses required are applied to the device. As the
device ages, the number of pulses required will continue to rise until it
exceeds the specified limit in the electrical characteristics of the part.
Once this has happened, the part is no longer able to be modified within
specifications. Eventually, if the memory is continually written and
erased, some of the bitcells will become completely saturated and
unable to be modified regardless of the number of pulses applied to
them.
As has already been discussed, preventing data disturbance and
damage to the FLASH array is of ultimate concern. If V
managed, either corruption of data or damage is likely to occur.
A brief mention should be made of some of the consequences of
improperly controlled voltage sources. For instance, if V
FP
is out of acceptable ranges and
o
C.
FP
FP
is improperly
is allowed to
MOTOROLA
AN1836