Contents
Which is the correct value for load capacitance?
One crystal manufacturer defines it like this: Another website has this to show for an answer: Quite many seem to think that the load capacitance is the value the crystal manufacturer recommends for the external capacitors. This, to me, seems completely incorrect. (But, as it turns out, might still work perfectly ok).
What should the capacitance of a crystal be?
If you want the crystal to oscillate as close as possible to the marked frequency, on average, you match up the total load capacitance to what the xtal maker has specified by specifying the two capacitors (usually they are both the same value, so you have only one degree of freedom).
How is the load capacitance of a parallel resonant Crystal calculated?
There’s a lot of seemingly conflicting information regarding how the load capacitance for a parallel resonant crystal is calculated. Faced with a lot of problems in recent years with non-oscillation and frequency inaccuracy, I’m asking the community’s help to get to the bottom of the problem.
What happens when capacitance is increased to 20 pF?
Here’s a picture showing the effect of increasing input and output capacitance from 1 pF up to 20 pF: – The X axis is at 9.9 MHz FYI. As you can possibly see, only when capacitance is 10 pF or 20 pF does the circuit produce 180 degrees of phase shift.
Do you need external capacitors for AVR microcontroller?
Most AVR microcontrollers have an internal capacitive load (CL1and CL2), so external capacitors are usually not needed. In some cases, however, the external load must be added to meet the crystal specifications. Some AVR microcontrollers can select whether the internal capacitors should be connected or disconnected with the CKOPT fuse.
Can a microcontroller function with an external crystal?
The end result is that nobody (except you) gets stuck guaranteeing your product will actually function with an external crystal. I suggest you read this technical note and referenced materials for starters. There is at least one entire book devoted to crystal oscillators.
How to choose crystal oscillator for Microchip microcontroller?
A crystal selection guide shows recommended crystals tested by experts and found suitable for various oscillator modules in different Microchip AVR®families. Test firmware and test reports from various crystal vendors are included. ©2018 Microchip Technology Inc.Application NoteDS00002648A-page 1