Crystal Oscillator 03——Causes of Crystal Oscillator Burnout
The first thing to be clear is that crystal oscillators are divided into two categories: passive crystal oscillators and active crystal oscillators. Based on the differences in the internal structure and working principle of these two types of crystal oscillators, the burnout of crystal oscillators can also be divided into two categories:
There are two points for the situation that the passive crystal oscillator is burned out:
1. Improper hand welding operation
If the lead parts are heated at high temperature or for a long time, it will cause damage to the silver-plated layer of the chip inside the crystal oscillator, excessive resistance and other problems, causing the crystal oscillator to fail to vibrate.
2. The excitation power is too large
According to different application fields, when choosing a crystal oscillator with appropriate excitation power, you must not arbitrarily change the excitation power input to the crystal oscillator by the circuit just to change the output frequency of the crystal oscillator.
Because excessive excitation power provided by the circuit may cause the vibration amplitude of the quartz crystal to become larger, so excessive heat generation causes the temperature of the vibration area of the quartz crystal to rise. The quartz wafer itself produces a gradient temperature rise, which directly destroys the frequency stability.
Because the degree of mechanical deformation of the chip may exceed the elastic limit, it will cause an irreversible displacement of the crystal lattice, resulting in a permanent frequency deviation of the output frequency of the crystal oscillator. In more serious cases, the quartz chip shatters, causing the crystal oscillator to completely stop vibrating (stop vibration), which is what we call "burning out".
The equivalent resistance becomes larger (note: the resistance value of the general crystal oscillator is 10~100Ω), which affects the start-up of the crystal oscillator, and in severe cases causes the crystal oscillator to stop vibrating. Excessive excitation power may also cause damage to the conductive glue that fixes the chip and the base, such as breakage. The consequence is that the internal circuit of the crystal oscillator is disconnected and the crystal oscillator stops vibrating.
In the circuit application of the passive crystal oscillator, the voltage applied to both ends of the crystal oscillator is very low, so it is very rare for the passive crystal oscillator to be burned out. However, such accidents more often occur in the improper application of active crystal oscillators, so special attention should be paid to them.
For the situation that the active crystal oscillator is burned out, it can also be divided into the following two points:
1. The voltage input is connected in the wrong direction
Common usage of quartz crystal oscillators: one pin is suspended, two pins are grounded, three pins are connected to output, and four pins are connected to voltage.
Correct voltage connection: the voltage input must be connected to the voltage input pin (VCC) of the crystal oscillator. If it is wrongly connected to the ground pin, the crystal oscillator will be "burned out" by the current.
2. Wrong selection of input voltage parameters
General input voltage: 1.8V, 2.8V, 3.3V, 5V. If 5V is supplied to an active crystal oscillator with a rated voltage of 1.8V, there will be a high risk of the crystal oscillator being burned out.
As shown below:
Active crystal oscillator 2.048MHz burnt out case
Active crystal oscillator 2.048MHz before welding, all electrical parameters are normal. After welding, the vibration stop phenomenon occurs.
For the inspection of the crystal oscillator, it was found that the electrode surface of the chip and the IC were normal, and the gold wire showed obvious fusing and balling, which caused the circuit to break.
The analysis shows that after the active crystal oscillator is energized, it is subjected to a voltage and current exceeding its own load, causing the gold wire to fuse, and the circuit appears to be open circuit, causing the crystal oscillator to stop vibrating. Subsequent verification proved this to be the case.
Special reminder for the active crystal oscillator: the active crystal oscillator will be broken down only when it is input with an overloaded high-voltage power supply. Do not connect the wrong or reversed input voltage.