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MSP430FR5994: CPU power consumption in VLO clock mode

Soumyajit Das
Genius 3340 points
Part Number: MSP430FR5994

Hi All,

 As per my understanding, the CPU can be made to run with the clock source as VLO which is around 10 kHz. I tried searching in the datasheet what would be the power consumption of the CPU running at this clock frequency. But I didn't get any info on this. In MSP430FR5994 datasheet (page no. 66) under article no. 6.4 'Operating Modes', its mentioned that active mode power consumption is 120uA/MHz (with FRAM active). Does this mean that at 10 kHz, the CPU power consumption will drop to 1.2uA (power consumption proportionately reduced)? I also found in article 5.5 (page 30) of the same document, the active supply current versus CPU (MCLK) clock frequency is represented in a graph, but the graph doesn't show values below 1 MHz.

Also, I have an application where the CPU needs to be in low power mode and occasionally wake-up to do some SD card & UART activity. During low power mode, ADC and external pulse counting is required. Is it possible to drive the CPU and ADC both using VLO? In my application, if the ADC voltage crosses a certain threshold while CPU is in low power mode, then the MCU should wake-up and start the UART activities. Is this achievable? It is okay in my application if the ADC conversion time is too high.

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Thanks

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Regards

Soumyajit

  • 0
    TI__Genius 9570 points
    Hi Soumyajit,

    Please refer to datasheet Chapter 5.4 to 5.9.

    Regards,
    Ling
  • 0 in reply to Ling Zhu2
    Genius 3340 points

    Hi Ling,

     Thanks for your reply. I have gone through the chapters 5.4 to 5.9, but nowhere any mention of CPU power consumption below 1 Mhz. My query is mainly related to CPU power consumption at VLO frequency of 10 kHz. In the attached image, please have a look at the highlighted text. It provides a formula for power consumption calculation. Is it applicable for MCLK below 1 MHz?

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    Thanks

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    Regards

    Soumyajit

  • 0 in reply to Soumyajit Das
    TI__Genius 9570 points
    Hi Soumyajit,

    If you go to Chapter 6.4, you will see that MCLK is off in LPM mode.

    Regards,
    Ling
  • 0 in reply to Ling Zhu2
    Genius 3340 points

    Hi Ling,
    Thanks once again for the quick reply. I would like to bring under notice that the entire context of the discussion in based out of active CPU mode and none of the LPM modes. My question about power consumption is to find out the CPU power consumption with low MCLK (VLO of 10 kHz) in active mode (not LPM mode).
    I checked article 6.4 of the datasheet which I saw long back, it does not mention power consumption at CPU frequencies below 1 MHz. In fact the active mode chosen to compare the power consumption is with reference to 16 MHz as maximum CPU clock rate. The mention of 120uA/MHz (with FRAM active) is the place from where I tried to deduce power consumption -> 120uA @ 1 MHz, hence 1.2uA @ 10 kHz. I know that this data (or my assumption) might be wrong. So, that's why I am trying to find out the CPU power consumption at 10 kHz (active mode).
    Hence, the question remains - what is the CPU power consumption at MCLK=VLO where the CPU is in active mode with FRAM active?
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    Thanks for your support
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    Regards
    Soumyajit

  • 0 in reply to Soumyajit Das
    TI__Genius 9570 points
    Hi Soumyajit,

    Sorry for the late reply. We don't have the power consumption data at MCLK=VLO. So please take the actual test data on your board.

    Regards,
    Ling
  • 0 in reply to Ling Zhu2
    Genius 3340 points
    Hi Ling,
    Thanks for the update. I will conduct the necessary tests to get the power consumption data.
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    Thanks
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    Regards
    Soumyajit

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