Avoided misconceptions in crystal oscillation selection
Due to the variety, size and electrical parameters of crystal vibration packaging,
it is easy to be confused or wrong to distinguish them. Therefore,
XTALONG suggests that you pay attention to the following eight points when selecting or purchasing crystal vibration:
① Determine the nominal frequency of crystal vibration, such as 32.768 KHz, 12 MHz, 125 MHz, etc.
② Determine whether the electric oscillation is passive or active. The circuit application between these two electric oscillations is different.
③ Determine whether the electric oscillation is DIP or SMD.
④ For passive electric oscillation, CL is required, such as 20PF, 9PF, 7PF or 12.5PF.
⑤ For active electric oscillations, Input Voltage is required, such as 1.8V, 2.8V or 3.3V.
⑥ Determine dimensions, such as 3.2MM*2.5MM, 2.0MM*1.6MM, 3.2MM*1.5MM, 2.0*1.6MM, etc.
⑦ Determine the accuracy of the electric oscillation, that is, at the normal temperature of about 25℃ ,
and at the actual operating temperature, the accuracy range of the required electric oscillation,
such as:±20PPM、±10PPM、±5PPM , etc. Generally, the actual operating temperature range of electric oscillation
includes: -20℃ ~+70℃ , -40℃ ~+85℃. Different fields of electronic products have different requirements for crystal oscillation accuracy.
⑧ Determine if the electric oscillation subsequently needs ultrasound. Crystal oscillation through ultrasound is at risk of being damaged to varying degrees, so special precautions/customizations are required.
PS:
① Judge the type of active electric oscillation：
For active electric oscillation, it is necessary to judge whether it is normal active electric oscillation,
temperature-supplemented electric oscillation or pressure-controlled electric oscillation from the model of electric oscillation.
The abbreviation of temperature-compensated oscillator is called TCXO, voltage-controlled oscillator is called VCXO,
and voltage-controlled temperature-compensated oscillator is called VC-TCXO.
② How to purchase 32.768KHz electric oscillation:
At present, the most common RTC patch electric oscillation is SMD3215 32.768KHz (FC-135). The specific parameters are as follows:
Frequency range: 32.768KHz
Volume: 3.2×1.5×0.9mm
Adjust Frequency Difference: +20ppm
Operating temperature (degree C): -40~+85
Load capacitance/Operating voltage: 7pF, 9pF, 12.5pF
Insulation impedance/Output mode: 70KΩ Max
Excitation power/Power consumption: 1.0μW Max.