Communications Clock PLL
MDS 2049-11 C
6
Revision 021402
Integrated Circuit Systems, Inc. q 525 Race Street San Jose, CA 95126 q tel (408) 295-9800 q
www.icst.com
MK2049-11
Recommended Loop Filter Values Vs. Output Frequency Range Selection
Loop Filter Capacitor Type
Loop filter capacitors C1 and C2 should be film type.
This includes the PPS polymer film type made by
Panasonic, or metal poly types made by MuRata or
Cornell Dublier.
The Panasonic ECP-U and ECH-U series capacitors
are typically used on the ICS MK20xx demo boards
and are found to work well. These devices are
available from Digi-Key.
Other acceptable capacitor types include those with
C0G or NP0 dielectric.
Avoid high-K dielectrics like Z5U and X7R (these are
acceptable for the decoupling capacitors, however).
The loop capacitors must have a high dielectric
resistance to avoid leakage-induced phase noise. For
this reason, DO NOT use any type of polarized or
electrolytic capacitors. Microphonics (mechanical
board vibration) will also induce output phase noise.
High-K dielectrics like Z5U and X7R have piezoelectric
properties that convert mechanical vibration into
voltage noise that interferes with VCXO operation.
For additional questions, please contact your ICS
Sales FAE or contact ICS MicroClock applications at
(408) 297-1201.
Power Supply Considerations
As with any integrated clock device, the MK2049-11
has a special set of power supply requirements:
The feed from the system power supply must be
filtered for noise that can cause output clock jitter.
Power supply noise sources include the system
switching power supply or other system components.
The noise can interfere with various internal device
circuit blocks such as the VCO or phase detector.
Each VDD pin must be decoupled individually to
prevent power supply noise generated by one device
circuit block from interfering with another circuit
block.
Clock noise from device VDD pins must not get onto
the PCB power plane or system EMI problems may
result.
This above set of requirements is served by the circuit
illustrated in the Recommended Power Supply
Connection, below. The main features of this circuit are
as follows:
Only one connection is made to the PCB power
plane.
The capacitors and ferrite chip (or ferrite bead) on
the common device supply form a lowpass ‘pi’ filter
that remove noise from the power supply as well as
clock noise back toward the supply. The bulk
FS3:1
Input
Clock
(ICLK)
External
Crystal
Freq
(MHz)
VCXO PLL
‘N’
(feedback
divider)
Value
RZ
C1
C2
Approximate
Loop
Bandwidth
(-3dB point)
Approximate
Damping
Factor
000
8 kHz
12.352
1544
2.7 M
0.1
F
330 pF
40 Hz
4
001
8 kHz
11.456
1432
2.7 M
0.1
F
330 pF
40 Hz
4
010
8 kHz
12.96
1620
2.7 M
0.1
F
330 pF
40 Hz
4
011
8 kHz
12.96
1620
2.7 M
0.1
F
330 pF
40 Hz
4
100 1.544 MHz
12.352
8
47 k
0.1
F
4.7 nF
180 Hz
1
Filter Option for Above Mode
22 k
1
F
47 nF
90 Hz
1.4
101
34.368
MHz
11.456
2
24 k
0.1
F
4.7 nF
400 Hz
1
Filter Option for Above Mode
11 k
1
F
47 nF
180 Hz
1.4
110
8 kHz
10.24
1280
2.7 M
0.1
F
330 pF
40 Hz
4
111
10-14 MHz
ICLK
6
43 k
0.1
F
4.7 nF
220 Hz
1
Filter Option for Above Mode
18 k
1
F
47 nF
100 Hz
1.4