DATASHEET
3.3 VOLT COMMUNICATIONS CLOCK PLL
Description
The MK2049-45A is a dual Phase-Locked Loop (PLL)
device which can provide frequency synthesis and jitter
attenuation. The first PLL is VCXO based and uses a
pullable crystal to track signal wander and attenuate input
jitter. The second PLL is a translator for frequency
multiplication. Basic configuration is determined by a
Mode/Frequency Selection Table. Loop bandwidth and
damping factor are programmable via external loop filter
component selection.
Buffer Mode accepts a 10 to 50 MHz input and will provide
a jitter attenuated output at 0.5 x ICLK, 1 x ICLK or 2 x
ICLK. In this mode the MK2049-45A is ideal for filtering jitter
from high frequency clocks.
In External Mode, ICLK accepts an 8 kHz clock and will
produce output frequencies from a table of common
communciations clock rates, CLK and CLK/2. This allows
for the generation of clocks frequency-locked to an 8 kHz
backplane clock, simplifying clock synchronization in
communications systems.
The MK2049-45A can be dynamically switched between T1,
E1, T3, E3 outputs with the same 24.576 MHz crystal.
IDT can customize these devices for many other different
frequencies. Contact your IDT representative for more
details.
MK2049-45A
Features
•
Packaged in 20-pin SOIC
•
3.3 V + 5% operation
•
Meets the TR62411, ETS300 011, and GR-1244
specification for MTIE, Pull-in/Hold-in Range, Phase
Transients, and Jitter Generation for Stratum 3, 4, and 4E
•
Accepts multiple inputs: 8 kHz backplane clock, or 10 to
50 MHz
•
Locks to 8 kHz + 100 ppm (External mode)
•
Buffer Mode allows jitter attenuation of 10 - 50 MHz input
and x1 / x0.5 or x1 / x2 outputs
•
Exact internal ratios enable zero ppm error
•
Output rates include T1, E1, T3, E3, and OC3
submultiples
•
Pb (lead) free package
•
See also the MK2049-34 and MK2049-36
Block Diagram
R
SET
ISET
C
P
C
S
R
S
CAP2
C
L
CAP1 X1
C
L
Optional Crystal Load Caps
External Pullable Crystal
X2
ICLK
Reference
Divider
(used in buffer
mode only)
Phase
Detector
VCXO
Charge
Pump
Reference
Divider
VCO
Output
Divider
Divide
by 2
CLK
CLK/2
VCXO
PLL
Feedback
Divider (N)
Translator
PLL
Feedback
Divider
8k
4
FS3:0
Divider Value
Look-up Table
IDT™
3.3 VOLT COMMUNICATIONS CLOCK PLL
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MK2049-45A
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MK2049-45A
3.3 VOLT COMMUNICATIONS CLOCK PLL
VCXO AND SYNTHESIZER
Pin Assignment
FS1
X2
X1
VDD
FCAP
VDD
GND
CLK
CLK/2
8k
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
FS0
RES
CAP2
GND
CAP1
VDD
GND
ICLK
FS3
FS2
Pin Descriptions
Pin
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Pin
Name
FS1
X2
X1
VDD
FCAP
VDD
GND
CLK
CLK/2
8k
FS2
FS3
ICLK
GND
VDD
CAP1
GND
Pin
Type
Input
Input
Input
Power
-
Power
Power
Output
Output
Output
Input
Input
Input
Power
Power
Loop
Filter
Power
Pin Description
Frequency select 1. Determines CLK input/outputs per table on page 2.
Internal pull-up resistor.
Crystal connection. Connect to a MHz crystal as shown in table on page 2.
Crystal connection. Connect to a MHz crystal as shown in table on page 2.
Power supply. Connect to +3.3 V.
Filter capacitor. Connect a 1000 pF ceramic capacitor to ground.
Power supply. Connect to +3.3 V.
Connect to ground
Clock output determined by status of FS3:0 per tables on page 2.
Clock output determined by status of FS3:0 per tables page 2. Always 1/2 of
CLK.
Recovered 8 kHz clock output.
Frequency select 2. Determines CLK input/outputs per table on page 2.
Internal pull-up resistor.
Frequency select 3. Determines CLK input/outputs per table on page 2.
Internal pull-up resistor.
Input clock connection. Connect to 8 kHz backplane or MHz clock.
Connect to ground.
Power Supply. Connect to +3.3 V.
Connect the loop filter capacitors and resistor between this pin and CAP2.
Connect to ground.
IDT™
3.3 VOLT COMMUNICATIONS CLOCK PLL
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MK2049-45A
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MK2049-45A
3.3 VOLT COMMUNICATIONS CLOCK PLL
VCXO AND SYNTHESIZER
Pin
Number
18
19
20
Pin
Name
CAP2
RES
FS0
Pin
Type
Loop
Filter
-
Input
Pin Description
Connect the loop filter capacitors and resistor between this pin and CAP1.
Connect a resistor to ground. See table.
Frequency select 0. Determines CLK input/outputs per table on page 2.
Internal pull-up resistor.
Output Decoding Table - External Mode (MHz)
ICLK
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
FS3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
FS2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
FS1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
FS0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
CLK/2
1.544
2.048
22.368
17.184
19.44
12.8
25.92
4.096
18.528
12.352
24.576
16.384
17.28
62.5
CLK
3.088
4.096
44.736
34.368
38.88
25.6
51.84
8.192
37.056
24.704
49.152
32.768
34.56
125
8k
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
8 kHz
Crystal
Used (MHz)
24.576
24.576
24.576
24.576
19.44
25.6
17.28
16.384
24.704
24.704
16.384
16.384
17.28
25
N
3072
3072
3072
3072
2430
3200
2160
2048
3088
3088
2048
2048
2160
3125
Output Decoding Table - Buffer Mode (MHz)
ICLK
20 - 50
10 - 25
FS3
1
1
FS2
1
1
FS1
1
1
FS0
0
1
CLK/2
ICLK
ICLK/2
CLK
2*ICLK
ICLK
8k
N/A
N/A
Crystal
ICLK/2
ICLK
N
3
3
0 = connect directly to ground, 1 = connect directly to VDD
Crystal is connected to pins 2 and 3; clock input is applied to pin 13.
Functional Description
The MK2049-45A is a clock generator IC that generates an
output clock directly from an internal VCXO circuit which
works in conjunction with an external quartz crystal. The
VCXO is controlled by an internal PLL (Phase Locked Loop)
circuit, enabling the device to perform clock regeneration
from an input reference clock. The MK2049-45A is
configured to provide a high frequency communications
reference clock output from an 8 kHz input clock or to jitter
attenuate and buffer a high frequency input clock. There are
14 selectable output frequencies and two buffer mode
selections. Please refer to the Output Clock Selection Table
on Page 2.
Most typical PLL clock devices use an internal VCO (Voltage
Controlled Oscillator) for output clock generation. By using
a VCXO with an external crystal, the MK2049-45A is able to
IDT™
3.3 VOLT COMMUNICATIONS CLOCK PLL
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MK2049-45A
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MK2049-45A
3.3 VOLT COMMUNICATIONS CLOCK PLL
VCXO AND SYNTHESIZER
generate a low jitter, low phase-noise output clock within a
low bandwidth PLL. This serves to provide input clock jitter
attenuation and enables stable operation with a low
frequency reference clock.
The VCXO circuit requires an external pullable crystal for
operation. External loop filter components enable a PLL
configuration with low loop bandwidth.
To obtain a list of qualified crystal devices please visit our
website.
PLL Loop Filter Components
All analog PLL circuits use a loop filter to establish operating
stability. The MK2049-45A uses external loop filter
components for the following reasons:
1) Larger loop filter capacitor values can be used, allowing
a lower loop bandwidth. This enables the use of lower input
clock reference frequencies and also input clock jitter
attenuation capabilities. Larger loop filter capacitors also
allow higher loop damping factors when less passband
peaking is desired.
2) The loop filter values can be user selected to optimize
loop response characteristics for a given application.
Referencing the External Component Schematic on this
page, the external loop filter is made up of components R
S
,
C
S
and C
P
. R
SET
establishes PLL charge pump current and
therefore influences loop filter characteristics.
Tools for optimizing the values of these four components
can be found on our web site.
Application Information
Output Frequency Configuration
The MK2049-45A is configured to generate a set of output
frequencies from an 8 kHz input clock. Please refer to the
Output Clock Selection Table on Page 2. Input bits FS3:0
are set according to this table, as is the external crystal
frequency. Please refer to the Quartz Crystal section on this
page regarding external crystal requirements.
Quartz Crystal
It is important that the correct type of quartz crystal is used
with the MK2049-45A. Failure to do so may result in reduced
frequency pullability range, inability of the loop to lock, or
excessive output phase jitter.
The MK2049-45A operates by phase-locking the VCXO
circuit to the input signal of the selected ICLK input. The
VCXO consists of the external crystal and the integrated
VCXO oscillator circuit. To achieve the best performance
and reliability, a crystal device with the recommended
parameters (shown below) must be used, and the layout
guidelines discussed in the PCB Layout Recommendations
section must be followed.
The frequency of oscillation of a quartz crystal is determined
by its cut and by the external load capacitance. The
MK2049-45A incorporates variable load capacitors on-chip
which “pull”, or change, the frequency of the crystal. The
crystals specified for use with the MK2049-45A are
designed to have zero frequency error when the total of
on-chip + stray capacitance is 14 pF. To achieve this, the
layout should use short traces between the MK2049-45A
and the crystal.
A complete description of the recommended crystal
parameters in the IDT application note, MAN05.
CAP2
C
P
0.0003 µF
R
S
820 kohms
C
S
0.1 µF
CAP1
Figure 3. Typical Loop Filter
IDT™
3.3 VOLT COMMUNICATIONS CLOCK PLL
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MK2049-45A
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MK2049-45A
3.3 VOLT COMMUNICATIONS CLOCK PLL
VCXO AND SYNTHESIZER
Charge Pump Current Table
R
SET
(k
13.02
15
16
18
20
22
24
27
36
47
56
75
100
150
200
Charge Pump Current
(I
CP
) (A)
139
125
119
109
100
93
86
68
56
43
35
28
22
15
12
Recommended Power Supply Connection for
Optimal Device Performance
VDD Pin
Connection to 3.3V
Power Plane
Bulk Decoupling Capacitor
(such as 1 µF Tantalum)
Ferrite
Bead
VDD Pin
VDD Pin
0.01 µF Decoupling Capacitors
Crystal Load Capacitors
The device crystal connections should include pads for
small capacitors from X1 to ground and from X2 to ground,
shown as C
L
in the External Component Schematic. These
capacitors are used to adjust the stray capacitance of the
board to match the nominally required crystal load
capacitance. Because load capacitance can only be
increased in this trimming process, it is important to keep
stray capacitance to a minimum by using very short PCB
traces (and no vias) been the crystal and device.
Please refer to MAN05 for the procedure to determine
capacitor values.
Special considerations must be made in choosing loop
components C
S
and C
P
. These recommendations can be
found on our web site.
Series Termination Resistor
Clock output traces over one inch should use series
termination. To series terminate a 50 trace (a commonly
used trace impedance), place a 33 resistor in series with
the clock line, as close to the clock output pin as possible.
The nominal impedance of the clock output is 20. (The
optional series termination resistor is not shown in the
External Component Schematic.)
PCB Layout Recommendations
For optimum device performance and lowest output phase
noise, the following guidelines should be observed. Please
also refer to the Recommended PCB Layout drawing on
Page 7.
1) Each 0.01 µF decoupling capacitor should be mounted on
the component side of the board as close to the VDD pin as
possible. No via’s should be used between decoupling
capacitor and VDD pin. The PCB trace to VDD pin should
be kept as short as possible, as should the PCB trace to the
ground via. Distance of the ferrite bead and bulk decoupling
from the device is less critical.
2) The loop filter components must also be placed close to
the CHGP and VIN pins. C
P
should be closest to the device.
Coupling of noise from other system signal traces should be
Decoupling Capacitors
As with any high performance mixed-signal IC, the
MK2049-45A must be isolated from system power supply
noise to perform optimally.
Decoupling capacitors of 0.01µF must be connected
between each VDD and the PCB ground plane. To further
guard against interfering system supply noise, the
MK2049-45A should use one common connection to the
PCB power plane as shown in the diagram on the next page.
The ferrite bead and bulk capacitor help reduce lower
frequency noise in the supply that can lead to output clock
phase modulation.
IDT™
3.3 VOLT COMMUNICATIONS CLOCK PLL
5
MK2049-45A
REV C 051310
嵌入式系统
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