Nonvolatile F-RAM Memory: A Superior Alternative to EEPROM in Automotive Applications
F-RAM is being designed into an increasing
number of automotive applications due to its
advanced memory properties. F-RAM has three
distinct advantages over EEPROM, the principal
competitor in automotive applications:
- High Speed Writes: Data are written at full bus speed via an SPI or I2C interface
- Virtually Unlimited Endurance: With a 1E14 endurance threshold, there is no practical limit to the number of times an F-RAM device can be written in an automotive application
- Low Power: Writing 64Kbits of data to F-RAM takes about 1/60th of the power required to write the same data to EEPROM
These technological advantages are being utilized
in a variety of automotive applications. The
examples below illustrate how F-RAM is used in
today’s advanced automobiles.
Position Control
F-RAM can be used in automotive
position control systems.
These include the position
controls that are found in
automatic windows, automatic
transmissions and parking
brakes, among other uses.
A position control can also be designed using an
absolute position encoder, but this device is often
more expense than the cost of an F-RAM device
plus a Hall effect sensor combined—making
F-RAM a cost effective alternative.
Figure 1. A nonvolatile record of a component’s current position
is made possible with a position sensor, such as a Hall sensor,
along with an F-RAM memory device.
F-RAM: The Robust Memory Choice
Only F-RAM has virtually unlimited number of write
cycles. F-RAM’s high write endurance makes it an
ideal memory choice given the high number of position
motor rotations that must be recorded in automobile
applications.
In automatic transmissions, the gear change mechanism
encounters harsh temperatures that require
AEC-Q100 Grade 1 qualification memory devices
(-40ºC to +125ºC). F-RAM has a small price adder
for this temperature range, but other nonvolatile
memory technologies have a much larger price
adder.
Infotainment Systems
Infotainment is becoming increasingly more
sophisticated in today’s automobiles, leading to
a demand for more data storage. The stored data
include volume settings, sound source, filter settings
(bass, midrange, treble), balance and user
favorites, etc. These settings may change with each
different sound source, such as CD, DVD, navigation
system, radio, etc.
Figure 2. Data storage on power fail
Why Use F-RAM Over EEPROM?
The data changes each time the system switches
between radio, CD, DVD, and navigation mode. All
of this data must be stored upon power fail. The
traditional EEPROM solution requires a significant
amount of capacitance to maintain power on the
EEPROM and MCU after the main power supply fails.
F-RAM eliminates the need for this capacitance,
thereby saving cost and space. Figure 2 compares
the amounts of data that can be stored by F-RAM
and EEPROM on power fail.
Event Data Recorder
The automobile Event Data Recorder (EDR) is similar
to the black box recorder on an aircraft. The EDR’s
function is to record detailed data before and during
an accident, which provides crucial information to
accident investigators.
The data must be written during an accident, so
designers must be aware that the main power
supply could fail. F-RAM is used in these EDR
applications for three reasons:
- High endurance: Event data - written to F-RAM prior to and during a crash - is not lost if the main power supply fails. F-RAM’s high endurance ensures data integrity.
- Fast writes, low power consumption: F-RAM can be written 1000x faster and a billion times more often than EEPROM, at a fractionof the power, so F-RAM-based EDRs can store data at higher intervals over the life of the EDR.
- No delay: Some event data need to be taken as often as every 1 millisecond to properly record crash events. Event data generated during a lateral side crash or ‘curb trip’ roll over need to be taken as often as every 1 millisecond. The slow, 10 millisecond write time and page buffer delay of an EEPROM makes it unsuitable for this purpose.
Figure 3. F-RAM’s fast write time and high endurance plays an
important role in the development of advanced EDRs that need
to collect many data parameters and store them as events
occur rapidly.
Serial F-RAM
Ramtron offers a wide range of serial F-RAM
memory densities that are AEC-Q100 Grade 3
Qualified (-40ºC to +85ºC) and AEC-Q100 Grade 1
Qualified (-40ºC to +125ºC). Added recently to our
automotive grade product list is the FM24CL64, a
I2C serial device with 64Kbit memory, available in a
SOIC 8-pin or TDFN 8-pin package.
Featured Products
| Part Number |
|
Description |
Data
Sheet |
App.
Notes |
|
| FM24C64-G |
|
64Kb Serial I2C F-RAM Memory (AEC-Q100 Grade 3)
|
|
|
|
| FM24CL16-G |
|
16Kb Serial I2C F-RAM Memory (AEC-Q100 Grade 3)
|
|
|
|
| FM24CL64-DG |
|
64Kb Serial I2C F-RAM Memory (AEC-Q100 Grade 3)
|
|
|
|
| FM25640-G |
|
64Kb Serial SPI F-RAM Memory (AEC-Q100 Grade 3)
|
|
|
|
| FM25C160-G |
|
16Kb Serial SPI F-RAM Memory (AEC-Q100 Grade 3)
|
|
|
|
| FM25L16-G |
|
16Kb Serial SPI F-RAM Memory (AEC-Q100 Grade 3)
|
|
|
|
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