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FRAM: Alternative to flash memory in embedded designs

Posted: 31 Jul 2012 ?? ?Print Version ?Bookmark and Share

Keywords:Ferroelectric random access memory? non-volatile? microcontrollers?

This peak power is mainly due to the usage of a charge pump and can reach values of up to 7mA, making non-volatile writes virtually taboo in the energy harvesting world [1]. With FRAM there is no charge pump; therefore, no high current writes. The average power when writing to FRAM is the same as when reading from or executing out of FRAM (i.e. there is no penalty for non-volatile writes, making FRAM a truly flexible option for energy harvesting applications.)

RFID tags
Radio frequency identification (RFID) tags are making an appearance in many places: store shelves for displaying prices, name badges at conferences and on industrial automation floors to mark and identify objects on a conveyor belt. Some of these applications require memory writes up to 100 times a day.

Consider a byte of flash memory with a typical endurance of 10K write/erase cycles. To achieve 100K write/erase cycle endurance, the application will have to set aside 10B of flash memory for every one byte of data, meeting the endurance requirements at the cost of high redundancy.

In comparison, an FRAM memory byte can endure 1015 write/erase cycles C 100 billion times more than a flash byte [3]. For applications that require high endurance in the order of millions of write/erase cycles, FRAM's endurance specification is unmatched by other embedded non-volatile memory technologies available today.

Handheld metering
Blood glucose metering is one example where loss of power is highly critical. In the case of power failure due to a depleted battery, the meter is required to save a time stamp, store the readings at the time of failure and perhaps even perform a few math functions before shutting down.

Consider a flash-based metering application with a battery that is depleted of charge, the power drop can be approximated to about 300mV in 0.01 seconds. In this time, up to 80K FRAM bytes can be written compared to about 8K bytes in flash. However this is without factoring in the high peak and average current requirements of a flash write, which will drain the battery rapidly, bringing down the backup capability significantly.

Another use case of system backup in power fail events is in energy metering where the energy reading needs to be preserved in non-volatile memory until power is restored. In such cases, the power usage during system backup is critical as backup battery sources are expected to last up to 10 years.

The list of applications where FRAM not only provides differentiation, but may also be the only viable option, is as diverse as is vast. To test drive an FRAM-based MCU check out the MSP430FR57xx series from Texas Instruments Incorporated (TI). Samples can be obtained for free and the MSP-EXP430FR5739 FRAM experimenter's board is available online for $29.

FRAM can lower system cost, increase system efficiency and reduce complexity while being significantly lower power than flash. If your existing flash-based MCU application has energy, write speed, endurance or power fail backup constraints it may be time to make the switch to FRAM.

References
[1] MSP430F2274 Flash-based MCU Datasheet www.ti.com/lit/pdf/slas504
[2] Maximizing FRAM Write Speed on the MSP430FR573x www.ti.com/lit/pdf/slaa498
[3] MSP430FR5739 FRAM-based MCU Datasheet www.ti.com/lit/pdf/slas639

About the author
Priya Thanigai is an applications engineer for Texas Instruments' MSP430 MCU applications and embedded software group. In addition to her experience with MSP430 MCU core architecture and wired communication protocols, her responsibilities include defining new product specifications and supporting deployment of MSP430 devices with a focus on FRAM-based MCUs. Thanigai holds a bachelor of science in electronics and communication engineering from the University of Madras, India and a master of science in electrical engineering from Northern Illinois University.

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