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