The reason why crystal oscillators cannot vibrate is revealed!

Crystal oscillator failure to vibrate is a common problem in electronic devices, which can affect the normal operation of the entire circuit. Below, we will introduce the main reasons why crystal oscillators do not vibrate.

1、 Parameter mismatch

1. Mismatch of load capacitance: If the electronic device actually needs to match 24MHz with 9PF, but chooses 24MHz with 12.5PF, this situation will cause the crystal oscillator to not vibrate. Suggest replacing it with a specification model that meets the requirements.

2. Large frequency error: Excessive frequency error causes the actual frequency to deviate from the nominal frequency, resulting in the crystal oscillator not oscillating. If this problem occurs, it should be replaced with a product with a suitable PPM value.

3. Inappropriate negative impedance: Excessive or insufficient negative impedance can cause the crystal oscillator to fail to vibrate. If the negative impedance is too high, the values of the external capacitors Cd and Cg of the crystal oscillator can be increased to reduce the negative impedance; If the negative impedance is too small, the values of the external capacitors Cd and Cg of the crystal oscillator can be reduced to increase the negative impedance. Generally speaking, the negative impedance value should be no less than 3 to 5 times the nominal maximum impedance of the crystal oscillator.

4. Inappropriate excitation level: Excessive or insufficient excitation level can also cause the crystal oscillator to fail to oscillate. The excitation level of the oscillation circuit to the crystal oscillator output can be adjusted by adjusting the resistance size in the circuit. Generally speaking, a smaller excitation level is beneficial for improving the stability of the circuit and extending the service life of the crystal oscillator, while also helping to reduce power consumption.

2、 Improper use

1. Base fracture: Base fracture may cause destructive physical external forces on the crystal oscillator, resulting in the internal chips of the crystal oscillator breaking due to tensile or twisting external forces, causing the phenomenon of no vibration. This may be due to the fact that the crystal oscillator did not add preheating action to the board before mounting, resulting in instantaneous thermal deformation of the board and destructive physical external force impact on the crystal oscillator base.

2. Irregular welding: Excessive temperature or time during welding can cause abnormal electrical performance indicators inside the crystal oscillator, resulting in the oscillator not vibrating. Suggest welding according to the recommended temperature and duration requirements. Virtual soldering can also affect the operation of the crystal oscillator. To rule out the possibility of poor soldering techniques, you can check whether the gap between the solder pad and the pin is too large. If it is too large, replace the appropriate solder pad. Generally, the diameter of the solder pad should be slightly larger than that of the pin.

3. Improper storage environment: Improper storage environment of crystal oscillators can lead to deterioration of their electrical performance and cause them to fail to vibrate. Long term use or storage under high temperature, low temperature, or high humidity conditions can cause deterioration of the electrical performance of the crystal oscillator, which may result in failure to vibrate. It is recommended to use and store under normal temperature and humidity conditions as much as possible to avoid the crystal oscillator or circuit board from getting damp.

4. MCU quality issues and software problems: Due to the uneven quality of MCUs in the market, non genuine products or problems with burning programs can directly cause the crystal oscillator to not vibrate. It is recommended to choose a reputable supplier to avoid purchasing non genuine MCUs; At the same time, ensure that the program is burned correctly.

5. EMC (Electromagnetic Compatibility) issues: EMC issues can also cause crystal oscillators to not vibrate. Among packaging materials, metal packaging products are superior to ceramic packaging products in terms of electromagnetic interference resistance. If the EMC on the circuit is high, metal packaging products should be selected as much as possible.

6. PCB wiring issue: The wiring design on the PCB board directly affects the performance of the circuit. If there are wiring errors (such as excessively long signal lines, interference caused by too close routing, failure to follow best wiring practices, etc.), they may affect the normal operation of the crystal oscillator. Therefore, the wiring of the crystal oscillator circuit should be as short and straight as possible, and as close to the MCU as possible to reduce the influence of stray capacitance in the oscillation circuit. In addition, signal lines cannot be routed underneath the crystal oscillator to avoid electromagnetic interference.

3、 Product Quality

1. Chip rupture: The chemical composition of the chip is silicon dioxide (similar to glass, it is a crisp and fragile product). If the crystal oscillator is subjected to significant impacts, drops, strong vibrations, or other external forces during production, manufacturing, or transportation, it can cause the internal chip to rupture or be damaged. If the chip ruptures, it is an irreversible physical phenomenon that directly causes the crystal oscillator to fail to vibrate. During the production process, it is necessary to avoid situations such as falling, heavy pressure, and impact; During transportation, foam materials shall be used for proper packaging to avoid midway damage. If the chip inside the crystal oscillator is indeed broken or damaged, it is recommended to replace the crystal oscillator directly.

2. Chip contamination: Impurities or dust during the electrode plating process of crystal chips can cause the crystal oscillator to fail to vibrate. If this situation occurs, it is recommended to replace the crystal oscillator directly.

3. Crystal oscillator leakage: Poor airtightness during the crystal oscillator manufacturing process or mechanical stress during welding can also cause the crystal oscillator to not vibrate. If this situation occurs, it is recommended to replace the crystal oscillator directly.

4. Conductive adhesive fracture: Conductive adhesive can fracture due to its own quality problems or improper processing. After the conductive adhesive fractures, it may cause the crystal oscillator to not vibrate or to vibrate intermittently, resulting in insufficient current intensity and inability to drive the chip to vibrate normally.

When the crystal oscillator fails to vibrate during its application, the reasons can usually be found from the above three items. If the crystal oscillator stops oscillating, it is necessary to check whether the crystal oscillator is overheating, which may be the reason for the high excitation level; If the crystal oscillator gradually stops oscillating during operation and starts working again by touching or heating the crystal oscillator pins with a soldering iron, the general reason is that the negative impedance value in the oscillation circuit is too small. It is necessary to adjust the values of the external capacitors Cd and Cg of the crystal oscillator to meet the loop gain of the oscillation circuit.

That's all for today's sharing, thank you for reading! The next episode will be even more exciting!