
MK2069-01
VCXO-BASED LINE CARD CLOCK SYNCHRONIZER
VCXO AND SYNTHESIZER
IDT VCXO-BASED LINE CARD CLOCK SYNCHRONIZER
8
MK2069-01
REV K 051310
Graph of Charge Pump Current vs. Value of RSET (external resistor)
Charge Pump Current, Example Settings from
Above Graph
Notes on Setting Charge Pump Current
The recommended range for the charge pump current is 25
μA to 300 μA. Below 25 μA, loop filter charge leakage, due
to PCB or capacitor leakage, can become a problem. This
loop filter leakage can cause locking problems, output clock
cycle slips, or low frequency phase noise.
As can be seen in the loop bandwidth and damping factor
equations or by using the filter response software available
from IDT, increasing charge pump current (ICP) increases
both bandwidth and damping factor.
VCXO Gain (KO) vs. XTAL Frequency
10E-6
100E-6
1E-3
100E+3
1E+6
10E+6
RSET, ohms
I CP
,A
m
ps
Recommended Range
of Operation
RSET
Charge Pump Current
(ICP)
5 M
Ω
25
μA
3 M
Ω
42
μA
2 M
Ω
65
μA
1 M
Ω
125
μA
480 k
Ω
255
μA
400 k
Ω
300
μA
10
20
15
25
3 0
2000
3000
4000
5000
6000
1000
C rys ta l Freq uency, M H z
VC
XO
G
a
in
(
K
O
),
H
z
p
e
r
V
o
lt