STM32 control schematic diagram, what are the functions of these three capacitors?

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STM32 control schematic diagram, what are the functions of these three capacitors? [Copy link]

 

Two capacitors are connected in parallel, and a CL is connected in the middle. Is this also a capacitor? What is the function of this circuit? Thank you

chenbingjy

CL is the crystal oscillator

maychang

chenbingjy posted on 2018-8-2 16:01 CL is the crystal oscillator

Y1 is the crystal. CL is the mark, indicating that the load capacitance should be 20pF.

chenbingjy

maychang posted on 2018-8-2 16:16 Y1 is the crystal. CL is the mark, indicating that the load capacitance should be 20pF.

Yes, yes, I made a mistake, that's what it means

maychang

CL = 20pF is a mark, the same as 8MHz below, used to explain Y1. Y1 is the label. Y1 is a quartz crystal (it may also be a piezoelectric ceramic resonator). C2C3 and Y1 are connected to the input (OSC IN) and output (OSC OUT) of an inverting amplifier (inside the microcontroller). This inverting amplifier, C2, C3, and Y1 form a Pierce crystal oscillator circuit.

ddllxxrr

This is the crystal capacitor, it has to be matched like this, in order to oscillate better, there are some things, don't ask why

qwqwqw2088

The smallest configuration unit of a single-chip microcomputer is a crystal oscillator.

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maychang posted on 2018-8-2 16:22 CL=20pF is a mark, just like the 8MHz below, used to illustrate Y1. Y1 is the label. Y1 is a quartz crystal (it may also be a piezoelectric ceramic resonator). ...

Very detailed, thank you!

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qwqwqw2088 posted on 2018-8-2 20:18 The smallest configuration unit of a microcontroller, a crystal oscillator is indispensable

Okay, I'm new to hardware, I'm a beginner.

topwon

If the crystal load capacitance CL=20pF, it may be a problem to use 10pF for the two matching capacitors (C2, C3) on the drawing. CL=C2//C3+Cic+Cs, Cic is the internal capacitance of the integrated circuit, and Cs is the capacitance on the PCB. The value of Cic+Cs is usually selected between 2~5pF. So C2 and C3 should be about 30pF.

topwon

Too much load capacitance deviation will cause difficulty in starting the crystal oscillator or increase the frequency deviation

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topwon posted on 2018-8-3 11:11 If the crystal's load capacitance CL=20pF, there may be a problem if the two matching capacitors (C2, C3) on the drawing are 10pF. CL=C2//C3+Cic+Cs, ...

Thank you very much for your guidance, very detailed.

懒猫爱飞

CL is a parameter of the crystal oscillator, which can be found in the crystal oscillator's specification sheet