When to use PLL and FLL in Kinetis KL15?

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When to use PLL and FLL in Kinetis KL15?

Contributor III

I'm using Kinets KL15.

Why is there a PLL and a FLL?

Which one should I choose and why?

4 Replies

Contributor III

The answer that was relevant to me is.

You need the FLL or PLL if you need to run the processor at 48 MHz or faster than the external crystal will run.

Whether you use the PLL or FLL depends on whether you want low power and to put the unit to sleep and wake up quickly.

You can run the FLL off of a 32khz crystal. The FLL also comes up faster than the PLL.

The PLL requires a 4MHz reference (I think roughly this is true) And takes longer to stabilize than the FLL.

Senior Contributor III

Other than the ranges as mentioned, an FLL is lower power, but is less accurate, and in certain conditions less stable, than a PLL.

The FLL produces an average multiple of the reference and changes between two or more different frequencies,  where as the PLL is capable of an exact multiple of the reference.

Contributor III

I found more restrictions (I think):

FLL: is up to 48MHz

PLL: is upp to100MHz

And the PLL draws 600µA at 48MHz.

So If i want MCGOUTCLK at 48MHz, should I prefer to select the FLL instead of the PLL (saving 600µA)?

Or is there some other benefits of selecting the PLL (not saving 600µA)?

0 Kudos

NXP Employee
NXP Employee

Hi, Markosiponen

There are many clock mode in KL series, As you kniow, the input source of FLL and PLL are different. PLL source is external clock and FLL can both from internal clock and external clock. The reference clock range are different. FLL reference clock is from 31.25KHz to 39.0625KHz. But PLL reference clock is from 2MHz to 4MHz. So you need to choose PLL and FLL according to your application. You can find chapter 4 clocking system in document "Kinetis L Peripheral Module Quick Reference". You can download this document from link http://cache.freescale.com/files/32bit/doc/quick_ref_guide/KLQRUG.pdf?fsrch=1&sr=4

Hope my reply can help you.

Best Regards