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SI52147 参数 Datasheet PDF下载

SI52147图片预览
型号: SI52147
PDF下载: 下载PDF文件 查看货源
内容描述: PCI - EXPRESS GEN 1 , GEN 2 ,与第3代九个输出时钟发生器 [PCI-EXPRESS GEN 1, GEN 2, & GEN 3 NINE OUTPUT CLOCK GENERATOR]
分类和应用: 时钟发生器输出元件PC
文件页数/大小: 22 页 / 182 K
品牌: SILICON [ SILICON ]
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Si52147  
2. Functional Description  
2.1. Crystal Recommendations  
The clock device requires a parallel resonance crystal. Substituting a series resonance crystal causes the clock  
device to operate at the wrong frequency and violates the ppm specification. For most applications there is a  
300 ppm frequency shift between series and parallel crystals due to incorrect loading.  
Table 4. Crystal Recommendations  
Frequency  
(Fund)  
Cut  
Loading Load Cap  
Shunt  
Cap (max)  
Motional  
(max)  
Tolerance  
(max)  
Stability  
(max)  
Aging  
(max)  
25 MHz  
AT  
Parallel 12–15 pF  
5 pF  
0.016 pF  
35 ppm  
30 ppm  
5 ppm  
2.1.1. Crystal Loading  
Crystal loading plays a critical role in achieving low ppm performance. To realize low ppm performance, use the  
total capacitance the crystal sees to calculate the appropriate capacitive loading (CL).  
Figure 1 shows a typical crystal configuration using the two trim capacitors. It is important that the trim capacitors  
are in series with the crystal. It is not true that load capacitors are in parallel with the crystal and are approximately  
equal to the load capacitance of the crystal.  
Figure 1. Crystal Capacitive Clarification  
2.1.2. Calculating Load Capacitors  
In addition to the standard external trim capacitors, consider the trace capacitance and pin capacitance to calculate  
the crystal loading correctly. Again, the capacitance on each side is in series with the crystal. The total capacitance  
on both side is twice the specified crystal load capacitance (CL). Trim capacitors are calculated to provide equal  
capacitive loading on both sides.  
Figure 2. Crystal Loading Example  
Preliminary Rev. 0.1  
7