MT9042CP1 Zarlink Semiconductor, Inc., MT9042CP1 Datasheet - Page 15

• Manufacturer Part Number: MT9042CP1
• Description: PLL, Dual Reference Frequency Selectable Digital PLL with Multiple Clock Outputs
• Manufacturer: Zarlink Semiconductor, Inc.

In cases where fast toggling might be expected of
the LOS1 input, then an unsymmetrical Guard Time
Circuit is recommended. This ensures that reference
switching doesn’t occur until the full guard time value
has expired. An unsymmetrical Guard Time Circuit
is shown in Figure 12.
Figure 13 shows a typical timing example of an
unsymmetrical Guard Time Circuit with the MT9042C
in Automatic Control.
NOTES:
1. T
bad to when the MT9042C is provided with a LOS indication.
MT9042C
MT9042C
D
Figure 13 - Unsymmetrical Guard Time
STATE
STATUS
STATUS
SIGNAL
SIGNAL
represents the time delay from when the reference goes
SEC
PRI
LOS2
LOS1
GTo
GTi
Figure 12 - Automatic Control, Unsymmetrical Guard Time Circuit Timing Example
GTo
GTi
V
NORMAL
150kΩ
SIH
1kΩ
GOOD
R
R
PRI
C
D
Circuit
1kΩ
R
P
HOLDOVER
T
BAD
D
PRI
10uF
C
+
NORMAL
GOOD
PRI
GOOD
TIE Correction (using GTi)
When Primary Holdover Mode is entered for short
time periods, TIE correction should not be enabled.
This will prevent unwanted accumulated phase
change between the input and output. This is mainly
applicable to Manual Control, since Automatic
Control together with the Guard Time Circuit
inherently operate in this manner.
For instance, 10 Normal to Holdover to Normal mode
change sequences occur, and in each case Holdover
was entered for 2s. Each mode change sequence
could account for a phase change as large as 350ns.
Thus, the accumulated phase change could be as
large as 3.5us, and, the overall MTIE could be as
large as 3.5us.
•
•
•
HOLDOVER
T
D
0.05ppm is the accuracy of Holdover Mode
50ns is the maximum phase continuity of the
MT9042C from Normal Mode to Holdover Mode
200ns is the maximum phase continuity of the
MT9042C from Holdover Mode to Normal Mode (with
or without TIE Corrector Circuit)
PRI
Phase hold
Phase state
Phase 10
BAD
=
=
10
=
NORMAL
0.05ppm 2s
50ns
×
SEC
(
250ns
+
200ns
×
+
100ns
=
=
NORMAL
250ns
MT9042C
100ns
GOOD
)
PRI
=
3.5us
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