Understanding Y1 Component
Thought for 26 sec
For ceramic resonators, the datasheet’s specified 4 pF load capacitance is the effective value seen by the resonator. In practice, you need to account for board stray capacitance (typically 1–3 pF) plus any input capacitance of the oscillator circuit. That means the actual external capacitor values can be slightly higher than 4 pF. A common and practical approach is to use two capacitors (one on each side of the resonator) in the range of 4.7 pF. This choice typically provides an effective load close to 4 pF when you factor in PCB parasitics.
In summary:
- Datasheet value: 4 pF effective load.
- Practical external capacitor option: Two ~4.7 pF capacitors (subject to your board’s stray capacitance).
You may fine-tune these values if you have a good estimate of your PCB stray capacitance, but 4.7 pF is a standard, widely used value in similar designs.
but previously you suggested 10pF with same calculations
Thought for 20 sec
There appears to be some confusion—let me clarify:
- The datasheet specifies a 4 pF effective load capacitance for proper oscillation.
- In practice, you must add the board’s stray capacitance (typically around 1–3 pF) to the external capacitors.
- If you calculate based on a typical stray capacitance (e.g., ~2 pF), you'll need external capacitors slightly higher than 4 pF to reach the effective 4 pF load. That often leads to using capacitors in the 4.7 pF range.
- The earlier reference to 10 pF was likely a misinterpretation or applicable to a different design scenario (for instance, when oversizing capacitance to ensure robust startup in a different oscillator configuration).
For your design following the datasheet recommendation, 4.7 pF capacitors on each side are usually a good option when accounting for stray capacitance.
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