MT9044AL1 Zarlink Semiconductor, Inc., MT9044AL1 Datasheet - Page 18

• Manufacturer Part Number: MT9044AL1
• Description: Dual Reference Frequency Selectable Digital PLL with Multiple Clock Outputs for T1/E1 (ITU-T G.812 type IV), Stratum (3, 4, 4E) and STS-3/OC3 Systems
• Manufacturer: Zarlink Semiconductor, Inc.

MT9044
Reset Circuit
A simple power up reset circuit with about a 50us
reset low time is shown in Figure 14. Resistor R
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.
18
MT9044
To Line 1
To Line 2
Figure 14 - Power-Up Reset Circuit
TX Line
TX Line
RX Line
RX Line
XFMR
XFMR
XFMR
XFMR
To
To
To
To
Figure 15 - Dual T1 Reference Sources with MT9044 in 1.544MHz Automatic Control
RST
TTIP
TRING
RTIP
RRING
TTIP
TRING
RTIP
RRING
MT9074
MT9074
MT8985
1kΩ
R
10kΩ
P
E1.5o
E1.5o
DSTo
DSTo
R
DSTi
DSTi
STo0
STo1
STi0
STi1
LOS
LOS
C4i
C4i
C4i
F0i
F0i
F0i
+5V
10nF
C
P
is
Dual T1 Reference Sources with MT9044 in
Automatic Control
For systems requiring simple state machine control,
the application circuit shown in Figure 15 using
Automatic Control may be used.
In this circuit, the MT9044 is operating Automatically,
using a Guard Time Circuit, and the LOS1 and LOS2
inputs to determine all mode changes. Since the
Guard Time Circuit is set to about 1s, all line
interruptions (LOS1=1) less than 1s will cause the
MT9044 to go from Primary Normal Mode to
Holdover Mode and not switch references. For line
interruptions greater than 1s, the MT9044 will switch
Modes
provided that the secondary signal is valid (LOS2=0).
After receiving a good primary signal (LOS1=0), the
MT9044 will switch back to Primary Normal Mode
For complete Automatic Control state machine
details, refer to Table 5 for the State Table, and
Figure 8 for the State Diagram.
+ 5V
1kΩ
10nF
from
10kΩ
SEC
TRST
RST
PRI
LOS1
LOS2
MS1
MS2
RSEL
MT9044
Holdover
OSCi
+ 5V
C4o
FS1
FS2
GTo
F0o
GTi
+ 5V
to
Out
150kΩ
20MHz
1kΩ
1kΩ
Secondary
CLOCK
±
32ppm
10uF
+
Normal,