Capacitance of a 32Mhz Crystal

[JK5]

If you look at the circuit of the PCA10040, it uses a 32Mhz 12pF crystal.

C1 and C2 of the crystal are 12 pF.

However, you say to use this formula: C1 = C_L * 2 - 4pF.

12pF*2 - 4pF = 20pF

Why use 12 pF instead of 20 pF?

[Search]

In the component parameters, the crystal oscillator also has load capacitance. Take PCA10040 as an example, the internal load capacitance of 32Mhz crystal oscillator is 8pF. Do you consider the internal load capacitance of crystal oscillator in your calculation?

[mathiaso]

Yes, C_L refers to the load capacitance found in the crystal's datasheet and a C1 and C2 of 12 pF is a result of a C_L = 8 pF,
⇒ C1 = C2 = 2*C_L - 4 pF = 2*8 pF - 4 pF = 12 pF.

[Search]

I have learned that in the nRF53 series, the chip has a bypass capacitor with a certain capacity value, and the designer can simplify the circuit by selecting the crystal oscillator that conforms to the chip parameters. Does this mean that the subsequent design of nordic, such as the 54 series, will also have a bypass capacitor in chips?

[mathiaso]

As there is still no open and public documentation for the nRF54 series, I suggest that you contact your local RSM for inquiries regarding this product series.

[JK5]

Thank you.
I was looking at the wrong datasheet.