MT9045 Zarlink Semiconductor, MT9045 Datasheet - Page 17

• Manufacturer Part Number: MT9045
• Description: T1/E1/OC3 System Synchronizer
• Manufacturer: Zarlink Semiconductor

For applications requiring
FOX F7C-2E3-20.0MHz
Frequency: 20MHz
Tolerance: 25ppm 0C to 70C
Rise & Fall Time:10ns (0.33V 2.97V 15pF)
Duty Cycle: 40% to 60%
The output clock should be connected directly (not AC coupled) to the OSCi input of the MT9045, and the OSCo
output should be left open as shown in Figure 8.
Crystal Oscillator - Alternatively, a Crystal Oscillator may be used. A complete oscillator circuit made up of a
crystal, resistor and capacitors is shown in Figure 9.
The accuracy of a crystal oscillator depends on the crystal tolerance as well as the load capacitance tolerance.
Typically, for a 20MHz crystal specified with a 32pF load capacitance, each 1pF change in load capacitance
contributes approximately 9ppm to the frequency deviation. Consequently, capacitor tolerances, and stray
capacitances have a major effect on the accuracy of the oscillator frequency.
The trimmer capacitor shown in Figure 9 may be used to compensate for capacitive effects. If accuracy is not a
concern, then the trimmer may be removed, the 39pF capacitor may be increased to 56pF, and a wider tolerance
crystal may be substituted.
±
32ppm clock accuracy, the following clock oscillator module may be used.
1uH inductor: may improve stability and is optional
Figure 9 - Crystal Oscillator Circuit
Figure 8 - Clock Oscillator Circuit
MT9045
OSCo
OSCo
OSCi
No Connection
OSCi
1MΩ
MT9045
Zarlink Semiconductor Inc.
MT9045
20MHz OUT
56pF
+3.3V
+3.3V
17
GND
100Ω
20MHz
39pF
1uH
0.1uF
3-50pF
Data Sheet