MT9040 Data Sheet
10
Zarlink Semiconductor Inc.
In Freerun Mode, the frequency tolerance at the clock outputs is identical to the frequency tolerance of the source
at the OSCi pin. For applications not requiring an accurate Freerun Mode, tolerance of the master timing source
may be
±100 ppm. For applications requiring an accurate Freerun Mode, such as AT&T TR62411, the tolerance of
the master timing source must be no greater than
±32 ppm.
Another consideration in determining the accuracy of the master timing source is the desired capture range. The
sum of the accuracy of the master timing source and the capture range of the MT9040 will always equal 230 ppm.
For example, if the master timing source is 100 ppm, then the capture range will be 130 ppm.
Clock Oscillator - when selecting a Clock Oscillator, numerous parameters must be considered. This includes
absolute frequency, frequency change over temperature, output rise and fall times, output levels and duty cycle.
Figure 5 - Clock Oscillator Circuit
For applications requiring
±32 ppm clock accuracy, the following clock oscillator module may be used.
FOX F7C-2E3-20.0MHz
Frequency: 20 MHz
Tolerance: 25 ppm 0C to 70C
Rise & Fall Time: 10 ns (0.33 V 2.97 V 15 pF)
Duty Cycle: 40% to 60%
CTS CB3LV-5I-20.0 MHz
Frequency: 20 MHz
Tolerance: 25 ppm
Rise & Fall Time: 10 ns
Duty Cycle: 45% to 55%
The output clock should be connected directly (not AC coupled) to the OSCi input of the MT9040, and the OSCo
output should be left open as shown in Figure 9.
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 6.
+3.3 V
20 MHz OUT
GND 0.1 uF
+3.3 V
OSCo
MT9040
OSCi
No Connection
