ICS84314 Datasheet, PDF (10/18 Pages) Integrated Circuit Systems – 350MHZ, CRYSTAL-TO-3.3V/2.5V LVPECL FREQUENCY SYNTHESIZER W/FANOUT BUFFER

Integrated
Circuit
Systems, Inc.
ICS84314
350MHZ, CRYSTAL-TO-3.3V/2.5V LVPECL
FREQUENCY SYNTHESIZER W/FANOUT BUFFER
TERMINATION FOR 2.5V LVPECL OUTPUT
Figure 4A and Figure 4B show examples of termination for 2.5V
LVPECL driver. These terminations are equivalent to terminat-
ing 50Ω to V_CC - 2V. For V_CC = 2.5V, the V_CC - 2V is very close to
ground level. The R3 in Figure 4A can be eliminated and the
termination is shown in Figure 4C.
VCCO=2.5V
Zo = 50 Ohm
Zo = 50 Ohm
2,5V LVPECL
Driv er
2.5V
+
-
R1
R2
50
50
R3
18
VC C O=2. 5V
Zo = 50 Ohm
Zo = 50 Ohm
2,5V LVPECL
Driv er
2.5V
R1
R3
250
250
2.5V
+
-
R2
62.5
R4
62.5
FIGURE 4A. 2.5V LVPECL DRIVER TERMINATION EXAMPLE
FIGURE 4B. 2.5V LVPECL DRIVER TERMINATION EXAMPLE
VCCO=2.5V
Zo = 50 Ohm
Zo = 50 Ohm
2,5V LVPECL
Driv er
2.5V
+
-
R1
R2
50
50
FIGURE 4C. 2.5V LVPECL TERMINATION EXAMPLE
CRYSTAL INPUT INTERFACE
The ICS84314 has been characterized with 18pF parallel resonant
crystals. The capacitor values, C1 and C2, shown in Figure 5 below
were determined using a 25MHz, 18pF parallel resonant crystal and
were chosen to minimize the ppm error. The optimum C1 and C2
values can be slightly adjusted for different board layouts.
84314AY
X1
18pF Parallel Cry stal
XTAL2
C1
22p
XTAL1
C2
22p
Figure 5. CRYSTAL INPUt INTERFACE
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10
REV. C JANUARY 27, 2005