AX88179
USB 3.0 to 10/100/1000M Gigabit Ethernet Controller
3.11 PLL Clock Generator
The AX88179 integrates internal oscillator circuits for 25 MHz, respectively, which allow the chip to operate cost
effectively with just external 25 MHz crystals.
The external 25 MHz crystal or oscillator, via pins XTL25P/XTL25N, provides the reference clock to internal oscillation
circuit to generate clock source for the embedded Ethernet PHY, embedded USB PHY, and base clock for ASIC use.
The external 25MHz Crystal spec is listed in below table. For more details on crystal timing, please refer to Section 7.5.1
“Clock Timing” and AX88179 Demo board schematic reference.
Parameter
Symbol
Typical Value
25.000000MHz
Nominal Frequency
Fo
Oscillation Mode
Fundamental
±30ppm
Frequency Tolerance(@25℃)
0℃ ~ +70℃, Commerical version
-40℃ ~ +85℃, Industrial version
±3ppm/year
Operation Temperature Range
Aging
Table 3
: The external 25MHz Crystal Units specifications
Figure 4
: 25MHz crystal oscillator diagram
15
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ASIX [ ASIX ELECTRONICS CORPORATION ]
