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MSP430F67671: use of high-frequency crystal oscillator

Andrey Bondarenko
Prodigy 40 points
Part Number: MSP430F67671

I'm interesting whether it is possible to use a high-frequency crystal oscillator on pins XIN and XOUT, or is it only supported by a 32,768 Hz clock generator? If there is no such support, is it right that I understand that there is no together support of 24-bit Sigma Delta DACs, 32 KB of RAM and high-frequency crystal oscillator installation in the msp430 processor family.The accuracy of the internal DKO does not match the parameters. Thank you.

  • 0
    TI__Expert 5490 points
    Hi Andrey,

    the XIN/XOUT pins are connected to XTAL1 which only supports up-to 32kHz.
    The MSPF67xx family of devices don't have an XTAL2 high-frequency crystal oscillator input.

    The MSP430F5xx/F6xx devices comes with the UCS (Unified Clock System) which supports an internal FLL. The accuracy of this FLL depends on the accuracy of the input source, which can be the XTAL1 32kHz crystal.

    What requirements do you have on accuracy of the clock?

    Best regards,
    Andre
  • 0 in reply to Andre Frantzke
    Prodigy 40 points
    Thanks for the reply Andre.
    I correctly understand that this is a DCO (digitally controlled oscillator). If so, in the datasheet, the temperature stability is indicated at 0.1% / ° С for 1 MHz, which is 12 MHz, in the temperature range of 40 ° C corresponds to 480 kHz. The temperature stability of the crystal oscillator at a level of ± 30-50 ppm, I would like the characteristics is not worse.
    Or is all this applicable only for work without an external generator?
    Thank you.
  • 0 in reply to Andrey Bondarenko
    TI__Expert 5490 points

    Hi Andrey,

    can you please elaborate your equation? How do you get to 480kHz?

    Andrey Bondarenko said:
    If so, in the datasheet, the temperature stability is indicated at 0.1% / ° С for 1 MHz, which is 12 MHz, in the temperature range of 40 ° C corresponds to 480 kHz.

    Best regards,

    Andre

     

  • 0 in reply to Andre Frantzke
    Prodigy 40 points
    The temperature stability is 0.1% / ° C, which corresponds to 12 kHz at a working frequency of 12 MHz. But how much I understand this is an error of 1 ° C. The operating range we need is 40 ° C, which corresponds to the temperature stability, over the entire temperature range, 480 kHz, or am I wrong?
  • 0 in reply to Andrey Bondarenko
    Guru 33653 points

    And what frequency / clock value do you need? XT2 value can be used divided as precision clock source for peripherals.

  • 0 in reply to Andrey Bondarenko
    TI__Expert 5490 points
    Hi,

    coming back to the dfDCO/dT DCO frequency temperature drift. At a temperature of 25 ° C the drift error is 0%.
    For every degree the temperature changes the default frequency changes by 0.1%.
    That means at a temperature of 40 ° C:
    deltaT=(40-25) ° C = 15 ° C
    error@40 ° C = 15 ° C * 0.1%/ ° C = 1.5%
    12MHz * 1.5% = 180kHz

    So at a temperature of 40 ° C you will have a nominal frequency of 12.18MHz. Please note, this is only nominal, because of the characteristic of a DCO we don't specify min/max values.

    Best regards,
    Andre
  • 0 in reply to Andre Frantzke
    Prodigy 40 points

    The logic of the calculation is the same, only the temperature range is not 15 ° C, but 50 ° C (-10 ° C ... + 40 ° C).

    Andre Frantzke said:
    The accuracy of this FLL depends on the accuracy of the input source, which can be the XTAL1 32kHz crystal.

    Does this mean that if at outputs XIN and XOUT there is 32,768 Hz clock generator, then the accuracy of the DCO will be similar to the accuracy of the crystal oscillator?

    Thank you!

  • 0 in reply to Andrey Bondarenko
    TI__Expert 5490 points
    Hi Andrey,

    The DCO will not have the accuracy of the external oscillator, as the FLL will jump between two DCO frequencies to achieve longterm frequency stability. That means cycle to cycles accuracy is lower, longterm accuracy is higher. As this is an adaptive process, we don't have any specifications for that.

    Best regards,
    Andre

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