SLAA502A July   2011  – September 2023 MSP430FR5720 , MSP430FR5721 , MSP430FR5722 , MSP430FR5723 , MSP430FR5724 , MSP430FR5725 , MSP430FR5726 , MSP430FR5727 , MSP430FR5728 , MSP430FR5729 , MSP430FR5730 , MSP430FR5731 , MSP430FR5732 , MSP430FR5733 , MSP430FR5734 , MSP430FR5735 , MSP430FR5736 , MSP430FR5737 , MSP430FR5738 , MSP430FR5739

 

  1.   1
  2.   Low-Power FRAM Microcontrollers and Their Applications
  3. 1What is FRAM?
  4. 2Why FRAM? – An Application Example
    1. 2.1 FRAM: A Universal Memory
    2. 2.2 Write Endurance
    3. 2.3 Fast Write
  5. 3Another Application Example: Light Switch
  6. 4Other Applications
  7. 5MSP430FR57xx Family
  8. 6Conclusion
  9. 7References
  10. 8Revision History

3 Another Application Example: Light Switch

The following application is a light switch that switches the lights via an RF link and harvests the energy from being switched. This means that the microcontroller and transceiver are not powered most of the time. Because of that, all data that needs to be retained must be stored in a non-volatile memory. The data that must be retained could be, for example, RF network parameters. In an intelligent light switch with dimming, additional status information could be stored.

In a flash-based microcontroller, the programming of a word would require a couple hundred nanocoulomb (nC) of charge (for example: ~100 µs × 2 mA = 200 nC), whereas in a FRAM-based microcontroller, the required charge to program the same amount of bits is on the order of two to three magnitudes (more than 100 times) smaller (for example: ~100 ns × 4 mA = 400 pC). Thus, with the same charge harvested from being switched, more than 100 times the amount of data can be permanently stored with a FRAM-based microcontroller compared to a Flash-based microcontroller. Alternatively, the energy harvesting circuitry can be dimensioned to provide and store less energy.

Of course, this example is applicable to all energy harvesting applications that can be unpowered for a certain time but still need to retain variable data.

Note: The charge required to program can vary from device to device and from manufacturer to manufacturer. The numbers shown here are only examples used to show the magnitude of difference.