ICS84321I Datasheet, PDF (10/16 Pages) Integrated Circuit Systems – 260MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
ICS84321I
260MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL
LVPECL FREQUENCY SYNTHESIZER
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS84321I provides sepa-
rate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V_CC, V_CCA, and V_CCO
should be individually connected to the power supply
plane through vias, and bypass capacitors should be
used for each pin. To achieve optimum jitter performance,
power supply isolation is required. Figure 4 illustrates how
a 24Ω resistor along with a 10µF and a .01µF bypass
capacitor should be connected to each V_CCA pin.
V_CC
V_CCA
3.3V
.01µF 24Ω
.01µF
10 µF
FIGURE 4. POWER SUPPLY FILTERING
LAYOUT GUIDELINE
The schematic of the ICS84321I layout example used in this lay-
out guideline is shown in Figure 5A. The ICS84321I recommended
PCB board layout for this example is shown in Figure 5B. This
layout example is used as a general guideline. The layout in the
actual system will depend on the selected component types, the
density of the components, the density of the traces, and the
stack up of the P.C. board.
U1
1
2
3
M5
M6
4
5
6
7
8
M7
M8
N0
N1
nc
VEE
ICS84321
C14
0.1u
C1
C2
X1
VCC
XTAL2
T_CLK
24
23
22
REF_IN
XTAL_SEL
nXTAL_SEL
VCCA
S_LOAD
S_DATA
S_CLOCK
21
20
19
18
17
S_LOAD
S_DATA
S_CLOCK
MR
VCCA
C11
0.01u
R7
24
C16
10u
C15
0.1u
Zo = 50 Ohm
IN+
TL1
Zo = 50 Ohm
IN-
TL2
VCC
R1
R3
125
125
+
-
R2
R4
84
84
84321AYI
FIGURE 5A. SCHEMATIC OF RECOMMENDED LAYOUT
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10
REV. A OCTOBER 10, 2003