Common passive crystal oscillator load capacitance CL is 20PF or 12.5PF (the latter is common in 32.768KHz crystal oscillator), if the equivalent input capacitance of electronic component pins (including circuit board stray capacitance Cs is included, Cs is generally estimated Value: 3~5PF or 4~6PF), you can try:
| CL | CL1/CL2 |
|---|---|
| 20PF | 30PF |
| 18PF | 27PF |
| 15PF | 22PF |
| 12.5PF | 18PF |
| 12PF | 18PF |
| 9PF | 12PF |
| 8PF | 10PF |
| 7PF | 8PF |
The above matching parameters of external capacitors are for reference only. Please refer to the actual output frequency accuracy of the crystal oscillator after the circuit board is powered on for the actual matching capacitor value.
The principle of adjusting the value of the external capacitor
If the measured crystal oscillator frequency is positive, such as crystal oscillator 12MHz, the measured frequency is 12.000840, try to fine-tune the capacitor value down.
If the measured crystal oscillator frequency is negative, such as crystal oscillator 12MHz, the measured frequency is 11.999060, try to fine-tune the capacitor value upwards.
The following table comes from the selection of crystal oscillator circuit capacitors :
| CL | CL1/CL2 |
|---|---|
| 20pF | 30~33pF |
| 16pF | 22~25pF |
| 12PF | 14~17pF |