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MSP430F2132: Minimum supply voltage for a 16 MHz DCO operation

Francois Charlot
Mastermind 22987 points
Part Number: MSP430F2132

Hello,

The MSP430F2132 datasheet seems contradictory as figure 1 shows that the 16 MHz operation is supported in the 3.3-3.6V range, when the last line of the Calibrated DCO Frequencies - Overall Tolerance on page 29 tells that 16 MHz is supported from 3.0 to 3.6V. Which voltage range should one consider?


Best regards,
François.

  • 0
    TI__Genius 14165 points

    Hi Francois,

    seems confusing but is not, please refer to the green marked notes below. The 3.3V requirement for the max speed is mainly for MCLK. Other modules can be clocked via SMCLK sourced by DCO while MCLK is e.g. sourced by an external 8 MHz crystal at DVCC = 3.0V.

    For example the Timer modules can operate at 3.0V with 16 MHz while e.g. the UART has the fsystem as max frequency specified. Hope this helps.

    Besides this I recommend to give some margin on DVCC when really operating at 16 MHz to ensure voltage drops due to load changes will not shortly violate the supply vs. frequency specs. 

  • 0 in reply to Dietmar Walther
    TI__Genius 14165 points

    Hi Francois,

    did the answer above helped or is anything missing? Please let us know otherwise I need to close this thread by end of the week due to inactivity.

  • 0 in reply to Dietmar Walther
    Prodigy 20 points

    Hi Dietmar, 

    I am part of the team from which the question originated.

    I'd like you to confirm my understanding, because some points are still unclear for me.

    In our application, a typical supply voltage of Vdd=3.3V is in reality roughly comprised between 3.0V and 3.6V (including all drifts and monitoring on power supplies).

    Note that this is the case in fact for most applications : 3.3V is usually within a 5 or 10% tolerance.

    My understanding is that in this concrete use case, it is in fact not possible  to use the MSP430F2132 at 16Mhz.

    To be clear : 

    If in the range 3.0V ; 3.6V, the microcontroller operates fine, in a recommanded operation state, but that the only impact is a degrtaded frequency precision (such as stated p28-29 between 15 and 17Mhz for example) : this is fine for us.

    However, if in these conditions the MSP enters in an unkown or not recommanded functioning mode, we cannot accept this and will be forced to operate at 12Mhz.

    This is still unclear to me especially because of pages 28-29 which provide information about fCAL. In the worst case conditions, fCAL is comprised between 15 and 17Mhz in the 3.0 to 3.6V voltage range. However, I have trouble understanding the relationship between fCAL (p28-29) and fSYSTEM (p18). Is fCAL (provided by DCO) only a subclock or is fCAL also the clock used by the system (i.e. fSYSTEM=fCAL).

    Sorry for insisting, but I really want to be certain that I'm not missing the opportunity to operate at 16Mhz which would be the best case scenario for me.

    Finally, one last question : If we understood correctly, then I have trouble imagining concrete applications which could operate at 16Mhz : the supply would need to be strictly between 3.3V and 3.6V, which is rather tight isn't it?

    Thanks again for your time, 

    Regards, 

    Antoine

  • 0 in reply to Antoine Canu
    TI__Genius 14165 points

    Antoine,

    got your points but the specification is pretty clear on this if you operate below 3.3V down to 3.0V it is not recommended to operate the CPU (MCLK) with 16 MHz because you would violate the "Operating Area" spec.

    So the fcal spec is intended to provide accuracy of the DCO calibration data at 3.0V which can be used for example to operate the Timer at 3.0V via SMCLK. This is possible.

    But I would not recommend to clock the CPU = MCLK with 16 MHz if the supply spec can go down to 3.0V. And this not only for degraded frequency accuracy it is simply a not specified operating range.

    So to you last questions to guarantee safe operation of the F2132 you're right and it is recommended to operate between 3.3 - 3.6V at maximum allowed system frequency (fsys).

  • 0 in reply to Dietmar Walther
    TI__Genius 14165 points

    If you need higher speed at lower supply voltage it might make sense to switch to a different family e.g. F5xx which can go down to 2.4V at 25 MHz or FRxxx which can go even lower at 16 MHz.

  • 0 in reply to Dietmar Walther
    Prodigy 20 points

    Thank you Dietmar for your comprehensive answer.

    I now have all the information I needed and I consider that you can close this topic.

    Have a good day, 

    Antoine

  • 0 in reply to Antoine Canu
    TI__Mastermind 22987 points

    Hello Antoine,

    Thank you for letting us know. We wish you the best for your projects.


    Best regards,
    François.

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