EFM32-chip peripherals-USB Crystal Oscillator Selection

One day, a customer reported that their new LG380 Board was not working properly. In addition, it is not normal to test several new proofing boards.

Dizzy, view the schematic, no problem. Check the PCB. However, the obvious difference is that LG needs an external 48 MHz crystal oscillator to implement the USB function.

Later, their engineers mentioned that the company's procurement had told him about the 48 MHz crystal oscillator, which he bought. So I guess the reason is that the USB is not working properly.

Let's take a look at what a wildcard crystal oscillator is. What is the difference between it and a normal crystal oscillator called a Fundamental Frequency Crystal Oscillator.

The crystal oscillator is made of a Z wafer, and the size and thickness of the Z wafer corresponding to different frequencies are different. Generally speaking, the higher the frequency of the Z crystal oscillator, the thinner the Z wafer. For example, a 40 MHz Z crystal requires a wafer thickness of 41.75mm, which can be achieved, but a 16.7mm MHz Z crystal requires a wafer thickness. Even if the thickness can be done but the cost is very high, the chip will be broken once it is merged into a finished product. Therefore, in high-frequency crystals, it is generally possible to use the technology of Tri-panic, five-panic, and seven-panic. The so-called wildcard is actually its higher harmonic.

For example, a crystal oscillator with a fundamental frequency of 16 MHz can obtain a 48 MHz frequency after three times of panic. In the market, the crystal oscillator with a 40 MHz or above is mostly a wildcard crystal oscillator.

Again, the usage of the wildcard crystal oscillator and the fundamental frequency crystal oscillator is also different. For example, the crystal of the fundamental frequency can work only by connecting the appropriate capacitor (figure 1 ), however, you must use the inductor and Capacitor together to obtain the pan-audio frequency. You must have a frequency selection network. Otherwise, you can only obtain the base frequency (figure 2 ).

Figure 1 Figure 2

As everyone is used to the circuit design in Figure 1, you can buy 48 MHz directly. If I have time, I will also test whether the pan-tone crystal oscillator can work normally on the LG board. In theory, it should work normally. Haha. For more information, see the document I searched from Baidu Library:

Http://download.csdn.net/detail/efm32/5078909

Therefore, when you use our LG/GG to develop USB, you must check the datasheet of the crystal oscillator. In fact, you only need to check the operation mode parameter in the crystal oscillator specifications to see if it is a wildcard crystal oscillator. If it is written as fundamental, it is a base-frequency crystal oscillator. If it is 3rd overtone, It is a three-time wildcard crystal oscillator.

 

2013.2.21. The original file link address is invalid.