Texas Instruments MSP430FR5739, User Manual

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Power Consumption at 13 kB/s (µA)
1
10
100
1000
10000
FRAM Flash
A
verage power (µA)
MSP-EXP430FR5739 User Experience Demo
www.ti.com
2.2.3.1 The Math Behind Mode 2
The MSP430F2274 device was used as a benchmark device to calculate the maximum flash write speed.
For a 512-byte block of flash, the following parameters were obtained from the MSP430F2274 data sheet:
Segment erase time = 4819 × t
FTG
= 16 ms
Where, t
FTG
= 1 / f
FTG
≈ 1 / 300 kHz
512 bytes write time ≈ 51.2 ms
Total time to write to 512 bytes ≈ 67.2 ms
Time to write to 100KB = 6.72 seconds, which calculates to 14.8 kBps
When measuring the speed of continuous flash writes on the bench, the observed speed is approximately
12 kBps, because the code execution overhead is added to the time calculated above.
This write speed is emulated with the FRAM device by maintaining a low active duty cycle and performing
one 512 byte block write every 40 ms.
Number of writes per second = 1 / 40 ms = 25
Number of bytes written per second = 512 × 25 = 12.800 kBps
The timing of the FRAM write is controlled by the VLO clock.
From these bench tests, it can be seen that writing 12 kBps to flash requires nearly 100% duty cycle,
while writing the same speed to FRAM requires less than 1% duty cycle. The rest of the time, the FRAM
device is in shutdown mode (LPM4), which results in an average current of less than 10
µ A. In
comparison, for a similar write speed, flash-based MCUs can require average current up to 2.2 mA.
Figure 3. Comparing Average Power When Writing to Nonvolatile Memory at 13 kBps
(MSP430FR5739 FRAM vs MSP430F2274 Flash)
2.2.3.2 Displaying Results on the PC GUI
When in Mode 2, the GUI provides details on the time elapsed in the mode, number of bytes written,
speed of emulated flash writes, and the endurance emulated over a 512 byte flash block.
The endurance is calculated based on the 10
4
program/erase cycles (minimum) for the MSP430F2274. If
a 512-byte block on a flash device were written to at a speed of 12.5 kBps (that is, 25 times per second),
the endurance would exceed the minimum limit in 10000/25 or 6.6 minutes.
Note that the MSP-EXP430FR5739 board only emulates this test to demonstrate a comparison in speed
and endurance between FRAM and flash; it does not perform the test on an actual flash device.
10 MSP-EXP430FR5739 FRAM Experimenter Board SLAU343B – May 2011 – Revised February 2012
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