
ICS843251-04
FEMTOCLOCKCRYSTAL-TO-3.3V LVPECL CLOCK GENERATOR
IDT / ICS 3.3V LVPECL CLOCK GENERATOR
9
ICS843S51AG-04 REV. A JANUARY 12, 2009
Schematic Example
Figure 5 shows an example of ICS843251-04 application
schematic. In this example, the device is operated at VCC = 3.3V.
The 18pF parallel resonant 25MHz crystal is used. The C1 = 33pF
and C2 = 27pF are recommended for frequency accuracy. For
different board layout, the C1 and C2 may be slightly adjusted for
optimizing frequency accuracy. Two examples of LVPECL
termination are shown in this schematic. Additional termination
approaches are shown in the LVPECL Termination Application
Note.
Figure 5. ICS843251-04 Schematic Example
X1
25MHz
C2
27pF
FREQ_SEL
C4
0.1u
R6
50
VCC
Zo = 50 Ohm
Set Logic
Input to
'0'
C3
0.1uF
Zo = 50 Ohm
R1
10
R4
82.5
C5
10u
1 8 p F
To Logic
Input
pins
VCCA
+
-
Optional
Y-Termination
3.3V
VCC
+
-
VCC=3.3V
R7
50
Zo = 50 Ohm
VCC
Logic Control Input Examples
R8
50
To Logic
Input
pins
R2
133
VCC
RD1
Not Install
R5
82.5
C1
33pF
RD2
1K
Set Logic
Input to
'1'
RU1
1K
U1
ICS843251I-04
1
2
3
4
8
7
6
5
VCCA
VEE
XTAL_OUT
XTAL_IN
VCC
Q
nQ
FREQ_SEL
RU2
Not Install
R3
133
VCC
Zo = 50 Ohm