MT9044AL Zarlink, MT9044AL Datasheet - Page 13

• 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

MT9044
Data Sheet
Holdover Mode
Holdover Mode is typically used for short durations (e.g., 2 seconds) while network synchronization is temporarily
disrupted.
In Holdover Mode, the MT9044 provides timing and synchronization signals, which are not locked to an external
reference signal, but are based on storage techniques. The storage value is determined while the device is in
Normal Mode and locked to an external reference signal.
When in Normal Mode, and locked to the input reference signal, a numerical value corresponding to the MT9044
output frequency is stored alternately in two memory locations every 30 ms. When the device is switched into
Holdover Mode, the value in memory from between 30 ms and 60 ms is used to set the output frequency of the
device.
The frequency accuracy of Holdover Mode is ±0.05ppm, which translates to a worst case 35 frame (125 us) slips in
24 hours. This meets the Bellcore GR-1244-CORE Stratum 3 requirement of ±0.37 ppm (255 frame slips per 24
hours).
Two factors affect the accuracy of Holdover Mode. One is drift on the Master Clock while in Holdover Mode, drift on
the Master Clock directly affects the Holdover Mode accuracy. Note that the absolute Master Clock (OSCi)
accuracy does not affect Holdover accuracy, only the change in OSCi accuracy while in Holdover. For example, a
±32 ppm master clock may have a temperature coefficient of ±0.1 ppm per degree C. So a 10 degree change in
temperature, while the MT9044 is in Holdover Mode may result in an additional offset (over the ±0.05 ppm) in
frequency accuracy of ±1 ppm, which is much greater than the ±0.05 ppm of the MT9044.
The other factor affecting accuracy is large jitter on the reference input prior (30 ms to 60 ms) to the mode switch.
For instance, jitter of 7.5 UI at 700 Hz may reduce the Holdover Mode accuracy from 0.05 ppm to 0.10 ppm.
Freerun Mode
Freerun Mode is typically used when a master clock source is required, or immediately following system power-up
before network synchronization is achieved.
In Freerun Mode, the MT9044 provides timing and synchronization signals which are based on the master clock
frequency (OSCi) only, and are not synchronized to the reference signals (PRI and SEC).
The accuracy of the output clock is equal to the accuracy of the master clock (OSCi). So if a ±32 ppm output clock
is required, the master clock must also be ±32 ppm. See Applications - Crystal and Clock Oscillator sections.
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Zarlink Semiconductor Inc.