ICS843004-01 Datasheet, PDF (9/15 Pages) Integrated Circuit Systems – FEMTOCLOCKS-TM CRYSTAL-TO- 3.3V LVPECL FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
ICS843004-01
FEMTOCLOCKS™ CRYSTAL-TO-
3.3V LVPECL FREQUENCY SYNTHESIZER
CRYSTAL INPUT INTERFACE
The ICS843004-01 has been characterized with 18pF paral-
lel resonant crystals. The capacitor values shown in Figure 3
below were determined using a 25MHz 18pF parallel reso-
nant crystal and were chosen to minimize the ppm error.
X1
18pF Parallel Crystal
XTAL_OUT
C1
33p
XTAL_IN
C2
27p
ICS843004-01
Figure 3. CRYSTAL INPUt INTERFACE
LAYOUT GUIDELINE
Figure 4 shows a schematic example of the ICS843004-01. An
example of LVEPCL termination is shown in this schematic. Ad-
ditional LVPECL termination approaches are shown in the
LVPECL Termination Application Note. In this example, an 18pF
parallel resonant 25MHz crystal is used. The C1=27pF and
C2=33pF are recommended for frequency accuracy. For differ-
ent board layout, the C1 and C2 may be slightly adjusted for
optimizing frequency accuracy.
VCC
R2
10 C3
10uF
Logic Control Input Examples
VCCA
C4
0.01u
VCC
C6
0.1u
Set Logic
VDD _{Input to}
'1'
RU1
1K
To Logic
Input
pins
RD1
Not Install
Set Logic
VDD _{Input to}
'0'
RU2
Not Install
To Logic
Input
pins
RD2
1K
U1
I C S843004-01
C2
33pF
X1
25MHz
18pF
C1
27pF
C9
0.1u
3.3V
R3
133
Zo = 50 Ohm
VCCO
C7
0.1u
Zo = 50 Ohm
R4
82.5
R5
133
+
-
R6
82.5
VCC=3.3V
VCCO=3.3V
R7
133
Zo = 50 Ohm
3. 3V
C8
0. 1u
Zo = 50 Ohm
R8
82.5
R9
133
+
-
R10
82.5
843004AG-01
FIGURE 4. ICS843004-01 SCHEMATIC EXAMPLE
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9
REV. B MAY 6, 2005