MK20: Internal Clock tolerance Query

[pj0585]

Hi,

I'm trying to see if I can use internal fast clock of 4Mhz (MK20DNxxxVLL10) instead of using external crystal. I could not find tolerance on the internal clock in datasheet over temperature, life or any other factor.

I want to see if I can use it for USB and CAN buses clock source.

Any inputs on the above will be helpful.

Regards, Pj

[kerryzhou]

Hi Prasant J,

  1,Internal 4Mhz IRC range is:

So, it is not very accurate, even you use it, you can't use the PLL or FLL to double it.

2. I want to see if I can use it for USB and CAN buses clock source.

If you are using the USB and CAN bus, there's no doubt, you can't use internal IRC, no matter slow or the faster.

You must use the external crystal as the USB and CAN clock source. USB need 48Mhz clock, CAN also need the accurate clock source.

Wish it helps you!

Have a great day,
Kerry

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[mjbcswitzerland]

Hi Pj

The specifications of the fast clock is something that seems to be missing in the data sheets of all Kinetis parts, however it is not needed to answer your questions.

For USB you have no choice but to use a suitably accurate crystal (such as 8MHz). And for CAN the crystal source is always recommended (lowest jitter) as clock too.

Regards

Mark