Hi Vignesh,
This is nearly the same question about the clock source.
About the clock accurate and reliable, it is determined by the clock source, if you use the inaccurate clock source, even you use the FLL, you can't get the accurate clock.
FLL locks the frequency to 1280 times the internal or external reference frequency. It can enlarge the clock source frequent.
Wish it helps you!
Have a great day,
Jingjing
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