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MSP430FR5849: how about the time duration to change DCO frequency?

Part Number: MSP430FR5849

Hi Sir,

My customer are using FR5849 in a power consumption critical application. They want to change DCO frequency to 1MHz in most of time, but change to 8Mhz when high speed calculation needed. They found when they change from 1M->8Mhz, it will need 900us to stable. And when change from 8MHz to 1MHz, it will need 120us.

They want to know is it normal? and why need 900us to do such DCO frequency change?

Best regards

Jacky Xu

  • Do you really need a stable frequency?
    If you are not using any critical communication (i.e. UART, I2C, SPI, etc...) @ 8MHZ, then you "might" not need to wait for the clock to stabilize. A multiply and shift will work the same @ 7.899MHz as it would @ 8.000MHz.
  • Jacky,

    It depends on the FLL lock time.
    There is a way to shorter the lock time: Save the tap value after FLL lock and re-load the tap value when next frequency change.

    Regards,
    Ling