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Does these two crystal need Cl load capacitor? ECS-.327-12.5-34R-C-TR for RTC and ECS-80-18-30B-AGN-TR 8Mhz

TVard.1
Associate III

ECS-.327-12.5-34R-C-TR for RTC  and ECS-80-18-30B-AGN-TR  8Mhz . do i need to connect the Load capacitor to it or they have inbuilt?

I have stm32f103 series MCU!

3 REPLIES 3
Peter BENSCH
ST Employee

These xtals are just plain ones containing just a crystal, so external capacitors are necessary.

BTW: a very good source for information and highly recommended to study is AN2867: Oscillator design guide for STM8AF/AL/S and STM32 microcontrollers.

Good luck!

/Peter

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TVard.1
Associate III

R external is is connected in series while in some other schematics the R external (oscillator) is connected in shunt. Do i need it?

Peter BENSCH
ST Employee

The AN2867 mentioned before discusses the Pierce oscillator used in STM32 and STM8 in section 3.5, which might require a serial external resistor to limit the power dissipated in the crystal. Except for 32kHz no general statement can be made as to whether Rext is necessary or not.

The external parallel resistor was used with old technologies (e.g. TTL) to set the operating point of the oscillator gate, but is no longer required with STM32 microcontrollers.

Does it answer your question?

/Peter

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