MT9044AL Zarlink, MT9044AL Datasheet - Page 20

• Manufacturer Part Number: MT9044AL
• Description: Framer E1/OC3/T1 5V 44-Pin MQFP
• Manufacturer: Zarlink

Specifications of MT9044AL

• Package: 44MQFP
• Maximum Data Rate: 2.048 Mbps
• Number Of Transceivers: 1
• Standard Framing Format: E1|OC3|T1
• Maximum Supply Current: 90 mA
• Minimum Single Supply Voltage: 4.5 V
• Maximum Single Supply Voltage: 5.5 V

The accuracy of a crystal oscillator depends on the crystal tolerance as well as the load capacitance tolerance.
Typically, for a 20 MHz crystal specified with a 32 pF load capacitance, each 1 pF change in load capacitance
contributes approximately 9 ppm 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 10 may be used to compensate for capacitive effects. If accuracy is not a
concern, then the trimmer may be removed, the 39 pF capacitor may be increased to 56 pF, 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.
Frequency:
Tolerance:
Oscillation Mode:
Resonance Mode:
Load Capacitance:
Maximum Series Resistance:
Approximate Drive Level:
e.g., CTS R1027-2BB-20.0 MHZ
(
Guard Time Adjustment
Excessive switching of the timing reference (from PRI to SEC) in the MT9044 can be minimized by first entering
Holdover Mode for a predetermined maximum time (i.e., guard time). If the degraded signal returns to normal
before the expiry of the guard time (e.g., 2.5 seconds), then the MT9044 is returned to its Normal Mode (with no
reference switch taking place). Otherwise, the reference input may be changed from Primary to Secondary.
±
20 ppm absolute,
±
6 ppm 0C to 50C, 32 pF, 25
20 MHz
As required
Fundamental
Parallel
32 pF
35
1 mW
1 uH inductor: may improve stability and is optional
Ω
MT9044
Figure 10 - Crystal Oscillator Circuit
OSCo
OSCi
1 MΩ
Ω
Zarlink Semiconductor Inc.
)
MT9044
56 pF
20
100 Ω
20 MHz
39 pF
1 uH
3-50 pF
Data Sheet