Question about the 32MhZ oscillator

[campestring]

Hello everyone I would like to produce my own custom board based on the NRF52840, but the quartz used in the Dk is sell by package of 3000 pcs so I decided to change and use this one : 

www.digikey.fr/.../6036218 

But I Don't know if I have to keep the two Capacitor : 12pF with the resonator ? 

I find Nothing in the datasheet of the resonator but I want to be sure of what I am doing.

Thank you have a good day,

Arnaud 

[JONATHAN LL]

Hi Arnaud,

I would not recommend to use the crystal you linked as it is not according to the specifications and (HFXO specification). 

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The crystal oscillator is designed for use with an AT-cut quartz crystal in parallel resonant mode. To achieve correct oscillation frequency, the load capacitance must match the specification in the crystal data sheet.

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Specs from BOM:
XTAL SMD 2016, 32 MHz, Cl=8 pF, Total Tol: ±40 ppm

This means it needs to be 8 pF and 60 Ohm and no more than ±40 ppm in total Tolerance.

Here are some example components that is within spec:
https://www.digikey.com/products/en/crystals-oscillators-resonators/crystals/171?k=&pkeyword=&sv=0&pv253=1398&pv253=1564&pv253=1940&pv253=2011&pv253=2439&sf=0&FV=-8%7C171%2C35%7C294760%2C46%7C8582%2Cmu60+Ohms%7C2082%2Cmu32MHz%7C2150&quantity=&ColumnSort=0&page=1&pageSize=25

I believe you can chose "cut tape" in digikey to by fewer components at the time.


Regards,
Jonathan

[campestring]

Hi, thank you for you reply ! 

for example if I choose this one : www.arrow.com/.../ecs-international 

Should I remove the two capacitor in the schematic ? Or should I leave them ?

Thank you have a good day.

best regards,

Arnaud

[JONATHAN LL]

Hi, 

You need to keep the two capacitors to load the crystal correctly. 

CL * 2 - 4pF = C1 = C2

The 4pF is  C_pcb + C_pin



Regards,
Jonathan