Shunt capacitance the same as stray capacitance?

Question

I needed a crystal for my project and I found this 16 MHz crystal: TXC 9C-16.000MAAJ-T.

To calculate the two capacitances for the crystal I used this equation:

C_L = (C₁ * C₂) / (C₁ + C₂) + C_stray

But the datasheet only gives C_shunt. Is it the same as C_stray?

After calculating with C_shunt for C_stray I come to a value of 22 pF.

For lowest power use Xtal’ rated for lowest pF and avoid ground plane under cct closest to IC for min. Stray pF — Tony Stewart EE75, Mar 30 '18 at 04:28
Changes are you may not need to know any more, but it has proven valuable to me since 1977. https://www5.epsondevice.com/en/information/technical_info/pdf/tech_notes_e201302.pdf and https://www5.epsondevice.com/en/information/technical_info/pdf/tech_notes_e_oscillator_circuit_evaluation_method_2.pdf — Tony Stewart EE75, Mar 30 '18 at 06:52
Does this answer your question? [Crystal oscillator load capacitance, again](https://electronics.stackexchange.com/questions/250608/crystal-oscillator-load-capacitance-again) — Tim Williams, Jul 19 '22 at 02:10

score 1 · Answer 1 · answered Mar 30 '18 at 00:55

1

The stray capacitance is the parasitic capacitance present on the pcb board (due to proximity to components) plus the capacitance of the pins. As a rule of thumb, a value for Cstray is on the order of ~5pF.

The shunt capacitance is another parameter and it's mainly a concern for the internal oscillator circuit.

answered Mar 30 '18 at 00:55

Big6

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thanks! So after calculate again it needs to be 26 pF. But i am using the atmega16 and the capacitors needs to be inbetween 12-22 pF. So is 22 the best option i think? – digitsboy Mar 30 '18 at 01:35

score 1 · Answer 2 · answered Dec 26 '21 at 23:28

A crystal is a wafer of piezoelectric material, usually quartz, between two metallic plates. The shunt capacitance is the capacitance of the plates and depends on the size of the plates, thickness of the wafer, and dielectric constant of the wafer material. This capacitance appears in parallel with the crystal and is the capacitance you would measure across the terminals with the crystal not oscillating.

Stray capacitance would be the capacitance between the crystal and other conductive materials such as circuit traces.

Shunt capacitance the same as stray capacitance?

2 Answers2