topic MK02 external clock in Kinetis Microcontrollers

MK02 external clock

massimopiazzabw — Tue, 09 Jun 2020 15:11:48 GMT

Hello
In a custom project we use MK02FN64VLF10 to generate low frequency sinusoidal waveform.
We need stability and precision for those waveform, so we don't use IRC clock, but external 8MHz clock generator instead.
Now, for a design review we need to reduce current consumption of board, and we use crystal oscillator... and here is the issue.
The MK02FN64VLF10 boots with IRC clock correctly, but internal oscillator with external crystal don't start, so we cannot switch system clock to oscillator source.
Can you help me?

Thank to all
Massimo

Re: MK02 external clock

Alexis_A — Thu, 11 Jun 2020 13:43:04 GMT

Hello Massimo,

Usually, this is due to the capacitance in the crystal is not enough to stabilize the crystal, I'll suggest checking the following application note.

Best Regards,

Alexis Andalon

Re: MK02 external clock

mjbcswitzerland — Thu, 11 Jun 2020 14:39:13 GMT

In the MCG register C2 there is a gain control. This must match with the crystal circuitry.

If the crystal is not loaded with caps and R use low gain mode. If it is loaded use high gain mode.

A mismatch will not allow the crystal oscillator to start up and is the most typical cause of the difficulty presently seen.

Regards

Mark

[uTasker project developer for Kinetis and i.MX RT]