MKW40Z using MEMS oscillator

[bryanvpi]

Is it possible to use a single output MEMS oscillator as the 32 MHz clock source, or must it be a crystal?

[lucianfiran]

The quartz part is very sensitive as it drives all - including BLE (IEEE 802.15.4) TX RX 2.4GHz - with should be very stable in frequency and time - is possible that the chip will not start.

Also you should look closely to oscillator parameters:

http://cache.nxp.com/files/32bit/doc/data_sheet/MKW40Z160.pdf
Page 39
        Cload Max Load Capacitance 10pF (max)
 http://cache.nxp.com/files/32bit/doc/ref_manual/MKW40Z160RM.pdf
Page 1077
Crystal resonator load capacitance 9PF typical, package shunt capacitance 2.8PF

More on topic:

How to calculate the value of crystal load capacitors? 

http://www.nxp.com/files/microcontrollers/doc/app_note/AN3208.pdf 

https://devzone.nordicsemi.com/question/4321/choosing-the-value-for-the-xtal-capacitors/
http://ww1.microchip.com/downloads/en/AppNotes/00826a.pdf
http://www.ti.com/lit/an/swra495d/swra495d.pdf
http://www.silabs.com/Support%20Documents/TechnicalDocs/AN551.pdf

[Jorge_Gonzalez]

Hello Bryan Sharp:

Yes, it should be possible to use the MEMS oscillator as external 32 MHz reference for the KW40. You need to set the bit MCG_C2[EREFS] as 1 to bypass the internal oscillator and use directly the external reference.

Just make sure that your oscillator complies with the oscillator specifications as stated in the Datasheet, in particular the +/-20ppm frequency error:

Best Regards!
Jorge Gonzalez

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