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What load capacitance should be soldered for an 8MHz crystal for an STM32F446RE Nucleo board?

Matthew K
Associate II

Hi, guys. I bought

  • STM32F446RE, mbed-Enabled Development Nucleo STM32F4 MCU 32-Bit ARM® Cortex®-M4 Embedded Evaluation Board

https://www.digikey.com/product-detail/en/stmicroelectronics/NUCLEO-F446RE/497-15882-ND/5347712

  • 8MHz ±10ppm Crystal 18pF 80 Ohms HC-49/US

https://www.digikey.com/product-detail/en/txc-corporation/9B-8.000MEEJ-B/887-1233-ND/2207653

0690X000006DMA5QAO.png

Form the product's image, I noticed X3 (8MHz crystal) is not populated.

I want to solder the above crystal and this has a load capacitance of 18pF.

I noticed the term "stray capacitance" of the printed circuit board and connections.

For the case when connecting a 8MHz crystal to the STM32F446RE Nucleo board/custom PCB that uses STM32F446RE,

  • how can I measure this stray capacitance?
  • what is the approximate "stray capcitance" of the STM32F446RE Nucleo board?
  • since the crystal's characteristic has a load capacitance of 18pF, what value of capacitor and resistor should be installed at C33, C34, R35, R37?

-Thanks!

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