MT9046 Zarlink Semiconductor, MT9046 Datasheet - Page 20

• Manufacturer Part Number: MT9046
• Description: T1/E1 System Synchronizer with Holdover
• Manufacturer: Zarlink Semiconductor

•
•
•
When 10 Normal to Holdover to Normal mode change sequences occur without MTIE enabled, and in each case
holdover was entered for 2s, each mode change sequence could still account for a phase change as large as
650 ns. However, there would be no accumulated phase change, since the input to output phase is re-aligned after
every Holdover to Normal state change. The overall MTIE would only be 650 ns.
Reset Circuit
A simple power up reset circuit with about a 50 us reset low time is shown in Figure 10. Resistor R
only and limits current into the RST pin during power down conditions. The reset low time is not critical but should
be greater than 300 ns.
Lock Indicator
The LOCK pin toggles at a random rate when the PLL is frequency locked to the input reference. In Figure 11 the
RC-time-constant circuit can be used to hold the high state of the LOCK pin.
Once the PLL is frequency locked to the input reference, the minimum duration of LOCK pin’s high state would be
32 ms and the maximum duration of LOCK pin’s low state would not exceed 1 second. The following equations can
be used to calculate the charge and discharge times of the capacitor.
t
C
=
0.2 ppm is the accuracy of Holdover Mode
50 ns is the maximum phase continuity of the MT9046 from Normal Mode to Holdover Mode
200 ns is the maximum phase continuity of the MT9046 from Holdover Mode to Normal Mode (with or
without TIE Corrector Circuit)
- R
t
R
C = Capacitor value (1 µF)
V
Schmitt Trigger (3.0 V)
C
T+
D
= Capacitor’s charge time
D
= Dynamic resistance of the diode (100 Ω)
= Positive going threshold voltage of the
C ln(1 – V
T+
/V
DD
) = 240 µs
Phase
Phase state
Phase 10
Figure 10 - Power-Up Reset Circuit
hold
MT9046
RST
=
Zarlink Semiconductor Inc.
=
=
10
0.2ppm 2s
50ns
MT9046
×
(
250ns
20
+
1 kΩ
200ns
R
×
10 kΩ
P
+
R
400ns
+3.3 V
=
=
400ns
250ns
)
10 nF
=
C
6.5us
P
is for protection
Data Sheet