MT9040 Zarlink Semiconductor, MT9040 Datasheet - Page 8

• Manufacturer Part Number: MT9040
• Manufacturer: Zarlink Semiconductor

MT9040
8
Applications
This section contains MT9040 application specific
details for clock and crystal operation, reset
operation, power supply decoupling, and control
operation.
Master Clock
The MT9040 can use either a clock or crystal as the
master timing source.
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
applications requiring an accurate Freerun Mode,
such as AT&T TR62411, the tolerance of the master
timing source must be no greater than
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 230ppm. For example, if the master
timing source is 100ppm, then the capture range will
be 130ppm.
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
MT9040
OSCo
OSCi
No Connection
Advance Information
20MHz OUT
+3.3V
+3.3V
GND
±
100ppm. For
±
0.1uF
32ppm.
For applications requiring
the following clock oscillator module may be used.
FOX F7C-2E3-20.0MHz
Frequency:
Tolerance:
Rise & Fall Time:
Duty Cycle:
CTS CB3LV-5I-20.0 MHz
Frequency:
Tolerance:
Rise & Fall Time:
Duty Cycle:
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 8.
Crystal
Oscillator may be used. A complete oscillator circuit
made up of a crystal, resistor and capacitors is
shown in Figure 6.
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 6 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.
1uH inductor: may improve stability and is optional
Figure 6 - Crystal Oscillator Circuit
Oscillator
OSCo
OSCi
1MΩ
MT9040
-
56pF
20MHz
25ppm 0C to 70C
10ns (0.33V 2.97V 15pF)
40% to 60%
20MHz
25ppm
10ns
45% to 55%
Alternatively,
100Ω
±
20MHz
32ppm clock accuracy,
39pF
1uH
a
3-50pF
Crystal