topic Re: KL02 Crystal Oscillator in Kinetis Microcontrollers

KL02 Crystal Oscillator

DustyStew — Fri, 11 Oct 2013 21:48:07 GMT

I'm wanting to use the MKL02Z32VFK4

I've just come across the part in the KL02 docs where they tell you it only operates with a 32KHz crystal. That was quite a surprise. I've just done a project with a K20, so I was expecting very much the same. I have not worked out the secret for finding details, given that the documentation is now designed to be somewhat device-independent. I can't seem to find what should be simple answers.

I am wondering about the repercussions. I presume this frequency can be multiplied up? What is the maximum crystal-controlled operating frequency? Is there a code example someone could provide?

I presume it is still possible to use an external oscillator to feed in a higher frequency?

What are the pros and cons of using a low-frequency (kHz) crystal rather than a MHz crystal?

Might I be better off using a different KL MCU, if I want to run that MCU at max clock rate, with a crystal-controlled oscillator?

Thx

Tom

Re: KL02 Crystal Oscillator

DustyStew — Fri, 11 Oct 2013 23:15:37 GMT

BTW looking at the circuit for the KL02 Freedom board, I see they have a 32k768 xtal with a 10M resistor and 2x12pF caps. I am wondering why the designer used these parts, because according to the docs for the OSC, the only valid mode is low power/low frequency, where no external caps and resistors is required. There are internal caps that will do 12pF in any case.

Any ideas? I am putting a crystal and a resistor on the board, need to wrap this one up so I can make some!

Re: KL02 Crystal Oscillator

Hui_Ma — Wed, 16 Oct 2013 07:36:31 GMT

KL02 MCG module is different with K20. KL02 only with FLL, without PLL. The FLL reference clock frequency is 32KHz.
That's why KL02 system oscillator only connect 32~40KHz external clock.
KL02 FLL is same with K20, which can multiple reference clock frequency and generate up to 48MHz clock output.

The FRDM-KL02Z oscillator circuit with load capactior and feedback resistor, while which with "DNP" mark means "Do Not Place".
On real FRDM-KL02Z board, there without load capactior and feedback resistor, which is using connection 1 of KL02 Reference manual Figure 22-2.

Wish it helps.