“Crystal oscillators are ubiquitous in modern devices, so the importance of crystal oscillators is self-evident. However, during the use of the crystal oscillator, some unexpected crystal oscillator failures often occur, such as why the crystal oscillator does not vibrate.
Crystal oscillators are ubiquitous in modern devices, so the importance of crystal oscillators is self-evident. However, during the use of the crystal oscillator, some unexpected crystal oscillator failures often occur, such as why the crystal oscillator does not vibrate.
In this article, firstly, we will introduce the reasons why the crystal oscillator does not oscillate and the solutions, and secondly, we will describe the countermeasures for CH340 crystal oscillator not oscillating for your reference. If you have some interest in the issues that will be discussed in this article, you may wish to continue reading.
It is a common phenomenon that the crystal oscillator of the single-chip microcomputer does not oscillate, so what are the reasons for the crystal oscillator not to oscillate? Let’s take a look.
1. The reason why the crystal oscillator does not vibrate
(1) PCB board wiring error;
(2) There is a problem with the quality of the single-chip microcomputer;
(3) There is a problem with the quality of the crystal oscillator;
(4) The load capacitance or matching capacitance does not match the crystal oscillator or there is a problem with the quality of the capacitance;
(5) The PCB board is damp, resulting in impedance mismatch and unable to vibrate;
(6) The trace of the crystal oscillator circuit is too long;
(7) There are traces between the two feet of the crystal oscillator;
(8) Influence of peripheral circuits.
(1) Eliminate the possibility of circuit errors, so you can compare with the recommended circuit of the corresponding type of microcontroller.
(2) Eliminate the possibility of bad peripheral components, because the peripheral components are nothing more than resistors and capacitors, you can easily identify whether they are good products.
(3) Eliminate the possibility that the crystal oscillator is a stop-oscillation product, because you will not only try one or two crystal oscillators.
(4) Try to change the capacitors at both ends of the crystal, maybe the crystal oscillator can start to vibrate. Please refer to the instruction manual of the crystal oscillator for the size of the capacitor.
(5) The traces of the crystal oscillator circuit should be as short as possible and as close to the IC as possible during PCB wiring, and avoid routing between the two pins of the crystal oscillator.
3. The difference, application range and usage of passive crystal and active crystal oscillator
1. Passive crystal – The passive crystal needs to use the oscillator on the DSP chip, and there are suggested connection methods on the datasheet. Passive crystals have no voltage problem, and the signal level is variable, that is to say, it is determined according to the start-up circuit. The same crystal can be applied to a variety of voltages, and can be used for a variety of DSPs with different clock signal voltage requirements. And the price is usually lower, so it is recommended to use crystals for general applications if conditions permit, which is especially suitable for producers with rich product lines and large batches. Compared with crystal oscillators, passive crystals have the disadvantage of poor signal quality. Usually, it is necessary to precisely match peripheral circuits (capacitors, inductors, resistors, etc. for signal matching). When replacing crystals with different frequencies, the peripheral configuration circuit needs to be adjusted accordingly. . It is recommended to use high-precision quartz crystals, and try not to use low-precision ceramics.
2. Active crystal oscillator – Active crystal oscillator does not need the internal oscillator of DSP, the signal quality is good, relatively stable, and the connection method is relatively simple (mainly for power supply filtering, usually a PI-type filter network composed of capacitors and inductors is used) , the output terminal can filter the signal with a small resistance resistor), no complicated configuration circuit is required. The usual usage of the active crystal oscillator: one pin is floating, the second pin is grounded, the third pin is connected to the output, and the fourth pin is connected to the voltage. Compared with passive crystals, the disadvantage of active crystal oscillators is that the signal level is fixed, and it is necessary to select the appropriate output level, which is less flexible and expensive. For applications with sensitive timing requirements, I personally think that an active crystal oscillator is better, because a relatively precise crystal oscillator or even a high-end temperature-compensated crystal oscillator can be used. Some DSPs do not have a start-up circuit inside, and can only use active crystal oscillators, such as TI’s 6000 series. Active crystal oscillators are usually larger than passive crystals, but now many active crystal oscillators are surface-mounted, and their volume is comparable to that of crystals, and some are even smaller than many crystals.
4. The phenomenon that the CH340 crystal oscillator does not vibrate and the solution
After connecting to the computer, the device can be discovered. (CH340, COM), but with an exclamation mark. Prompt “This device is not working correctly because Windows cannot load the drivers required for this device. (Code 31)”
Observed with an oscilloscope, it was found that the crystal did not vibrate.
1. Replace the crystal first; no
2. Then check the schematic diagram against the data sheet, and found that the V3 pin should be connected to a 0.01uF capacitor, but I used 0.1uF, and found that it still does not work.
3, replace the chip, no.
4. Replace the USB cable, no.
5. Later, on the official BBS, the crystal does not vibrate. Specifically, the crystal starts to vibrate at the moment of power-on, and it will be a high level later.
Measured with an oscilloscope and found mine too. But his that is because the signal line D+D- is not shielded. Although the problem is not solved, there are both enlightenment and progress.
In addition, another information is obtained. If the communication between CH340 and the computer is abnormal, the chip will enter the sleep state, and the crystal will not vibrate at this time. That is to say, the crystal does not vibrate is not necessarily a problem with the device hardware. Also related to the host computer.
6. I downloaded the latest driver from the official website, but it still doesn’t work.
7. Finally, thanks to Du Niang, search for the above prompt “This device is working abnormally because Windows cannot load the drivers required for this device. (Code 31)”, there is an answer as follows “Manually delete from the device manager” This hardware information, and then scan the hardware changes should be able to find this hardware information, no need for the system to automatically search for the driver, but to manually point to the folder where the driver is located, (if there is no driver, you can download and unzip it in advance.) In this way, you can Reinstall its drivers.”
According to the operation, it can be recognized normally.