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MSP430F5438A: Max deviation of RTC component in the MSP430 MCUs

Ron Shem
Intellectual 510 points

Part Number: MSP430F5438A

Hi

I considering using one of these MSP MCUs

MSP430F5438A    or

MSP430FR5994

As I saw these MCU has ultra low energy consumption and also has a RTC build-in component.

How can I know the max deviation of the RTC ?

The app will work in open area in temperature of (-10) to 60 Celsius degrees.  I need it will have deviation of not more than 2 hours per ten years.

Were can I find this information? Didn't see any mention at the product datasheet description section.

Thanks

  • 0
    TI__Guru 71216 points

    Hi Ron,

    Typically you will use an external 32Khz crystal to drive the clock in the RTC.  It is the accuracy of the crystal, not the MSP430RTC, that controls the overall accuracy.  There are many different manufacturers of crystals, so you can refer to their datasheet for the accuracy over temperature specification.  Typically 50ppm or better is required.

  • 0 in reply to Dennis Lehman
    Intellectual 510 points

    Thanks

    Does ppm units in context of RTCs will usually be in seconds?

  • 0 in reply to Ron Shem
    Guru 102865 points

    You asked for 2 hours in 10 years, which my calculator says is 2/(10*365.25*24)= ~0.000023 = .0023% = 23ppm.

    It's not hard to find a 32kHz crystal at 20ppm over a reasonable temperature range. Be sure to check the aging spec, since you want it for >= 10 years.

  • 0 in reply to Bruce McKenney
    TI__Guru 71216 points

    Hello Ron,

    I’m assuming you were able to move forward with your design.
    If this isn’t the case, please click the "This did NOT resolve my issue" button and reply to this thread with more information.
    If this thread locks, please click the "Ask a related question" button and in the new thread describe the current status of your issue and any additional details you may have to assist us in helping to solve your issues.

    BTW - Thank you Bruce for narrowing in on the required ppm.

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