MT9041B
For applications requiring
±32ppm
clock accuracy,
the following clock oscillator module may be used.
CTS CXO-65-HG-5-C-20.0MHz
Frequency:
20MHz
Tolerance:
25ppm 0C to 70C
Rise & Fall Time:
8ns (0.5V 4.5V 50pF)
Duty Cycle:
45% to 55%
Advance Information
Frequency:
20MHz
Tolerance:
As required
Oscillation Mode:
Fundamental
Resonance Mode:
Parallel
Load Capacitance:
32pF
Maximum Series Resistance:
35
Ω
Approximate Drive Level:
1mW
e.g., CTS R1027-2BB-20.0MHZ
(
±
20ppm absolute,
±
6ppm 0C to 50C, 32pF, 25
Ω
)
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
- Alternatively, a Crystal
Oscillator may be used. A complete oscillator circuit
made up of a crystal, resistor and capacitors is
shown in Figure 6.
MT9041B
OSCi
20MHz
1MΩ
Reset Circuit
A simple power up reset circuit with about a 50us
reset low time is shown in Figure 7. Resistor R
P
is for
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.
MT9041B
+5V
R
10kΩ
RST
56pF
OSCo
100Ω
39pF
3-50pF
R
P
1kΩ
C
10nF
1uH
1uH inductor: may improve stability and is optional
Figure 7 - Power-Up Reset Circuit
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.
C1
0.1uF
Figure 6 - Crystal Oscillator Circuit
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.
+
18
15
MT9041B
1
C2
0.1uF
5
Figure 8 - Power Supply Decoupling
8
+
MITEL [ MITEL NETWORKS CORPORATION ]
