MT9041B Mitel Networks Corporation, MT9041B Datasheet - Page 8

• Manufacturer Part Number: MT9041B
• Description: T1/E1 System Synchronizer
• Manufacturer: Mitel Networks Corporation

MT9041B
For applications requiring
the following clock oscillator module may be used.
CTS CXO-65-HG-5-C-20.0MHz
Frequency:
Tolerance:
Rise & Fall Time:
Duty Cycle:
The output clock should be connected directly (not
AC coupled) to the OSCi input of the MT9041B, and
the OSCo output should be left open as shown in
Figure 5.
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.
The crystal should be a fundamental mode type - not
an overtone. The fundamental mode crystal permits
a simpler oscillator circuit with no additional filter
components and is less likely to generate spurious
responses. The crystal specification is as follows.
8
1uH inductor: may improve stability and is optional
MT9041B
Figure 6 - Crystal Oscillator Circuit
Oscillator
OSCo
OSCi
1M
56pF
-
20MHz
25ppm 0C to 70C
8ns (0.5V 4.5V 50pF)
45% to 55%
Alternatively,
100
20MHz
32ppm clock accuracy,
39pF
1uH
a
3-50pF
Crystal
Frequency:
Tolerance:
Oscillation Mode:
Resonance Mode:
Load Capacitance:
Maximum Series Resistance:
Approximate Drive Level:
e.g., CTS R1027-2BB-20.0MHZ
( 20ppm absolute, 6ppm 0C to 50C, 32pF, 25 )
Reset Circuit
A simple power up reset circuit with about a 50us
reset low time is shown in Figure 7. Resistor R
protection only and limits current into the RST pin
during power down conditions. The reset low time is
not critical but should be greater than 300ns.
Power Supply Decoupling
The MT9041B has two VDD (+5V) pins and two VSS
(GND) pins. Power and decoupling capacitors should
be included as shown in Figure 8.
MT9041B
Figure 8 - Power Supply Decoupling
Figure 7 - Power-Up Reset Circuit
0.1uF
C2
RST
18
1
15
0.1uF
C1
1k
R
Advance Information
P
5
10k
R
20MHz
As required
Fundamental
Parallel
32pF
35
1mW
MT9041B
+5V
10nF
C
P
is for