STM32F405RGT6接8MHz晶振采用多大电容?

STM32F405RGT6接8MHz晶振采用多大电容?解释如下:

For CL1 and CL2, it is recommended to use high-quality external ceramic capacitors in the 5 pF to 25 pF range (typ.), designed for high-frequency applications, and selected to match the requirements of the crystal resonator. CL1 and CL2 are usually the same size. The crystal manufacturer typically specifies a load capacitance which is the series combination of CL1 and CL2. PCB and MCU pin capacitance must be included (3~5pF) can be used as a rough estimate of the combined pin and board capacitance) when sizing CL1 and CL2.

STM32F405RGT6接8MHz晶振采用多大电容?

对于外接电容CL1和CL2取值,建议在5pF至25pF范围(典型值)之内选择高品质的外置陶瓷电容器,以匹配专为高频应用而设计的晶体谐振器应用之要求。通常,外接电容CL1和CL2等值选取。晶体制造商会指定一个负载电容(CL),即CL1 和 CL2 的串联组合。在计算晶振外接负载电容时,请必须包括 PCB 和 MCU 引脚电容在内,一般杂散电容(Cs)按照3~5pF估算。

STM32F405RGT6接8MHz晶振采用多大电容?

举例如下:

  • 如果晶振负载电容(CL)=12pF,外接电容CL1=CL2≈15pF;
  • 如果晶振负载电容(CL)=15pF,外接电容CL1=CL2≈18pF;
  • 如果晶振负载电容(CL)=20pF,外接电容CL1=CL2≈27pF。

基于杂散电容为估算值,建议上电实测8MHz晶振(晶体谐振器)输出频率,并根据实测数据来调整外接电容大小。

外接电容(CL1&CL2)调整规律:

若晶振输出频率偏负(-ppm),请减小外接电容;若频率偏正(+ppm),请增大外接电容。

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