ICS84325 データシートの表示（PDF） - Integrated Circuit Systems
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ICS84325 Datasheet PDF : 15 Pages
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Integrated
Circuit
Systems, Inc.
ICS84325
CRYSTAL-TO-3.3V LVPECL
FREQUENCY SYNTHESIZER WITH FANOUT BUFFER
CRYSTAL INPUT INTERFACE
The ICS84325 has been characterized with 18pF parallel resonant
crystals. The capacitor values, C1 and C2, shown in Figure 3 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.
X1
18pF Parallel Cry stal
XTAL2
C1
22p
XTAL1
C2
22p
Figure 4. CRYSTAL INPUt INTERFACE
SCHEMATIC EXAMPLE
Figure 5A shows a schematic example of using an ICS84325. In
this example, the input is a 25MHz parallel resonant crystal with
load capacitor CL=18pF. The frequency fine tuning capacitors
C1 and C2 are 22pF respectively. This example also shows logic
control input handling. The configuration is set at F_SEL[1:0]=11
therefore the output frequency is 250MHz. It is recommended to
have one decouple capacitor per power pin. Each decoupling
capacitor should be located as close as possible to the power
pin. The low pass filter R7, C11 and C16 for clean analog supply
should also be located as close to the VCCA pin as possible.
VCC
VCC
R7
24
C 11
0.1u
C16
10u
VCC
VCCA
22p
C1
X1
25MHz,18pF
C2
22p
R4 VCC
1K
F_SEL1
R5 F_SEL0
1K
U7
13
14
15
16
VC C
VEE
PLL_SEL
17 VCC
18 VCCA
19
20
21
VEE
XTAL2
XTAL1
22 MR
23
24
F_SEL1
F_SEL0
VC C
I C S84325
nQ5
Q5
nQ4
12
11
10
9
Q4 8
nQ3 7
Q3
nQ2
Q2
6
5
4
nQ1 3
Q1
nQ0
Q0
2
1
Zo = 50
Zo = 50
R2
50
RU2
1K
RU3
1K
F_SEL1
F_SEL0
VCC=3.3V
(U1,13) VCC
(U 1, 16)
(U1,24)
RD2
SP
RD3
SP
e.g. F_SEL[1:0]=11
SP = Spare, Not Installed
C6
0.1u
C5
0.1u
C3
0.1u
-
+
R1
50
R3
50
84325EM
FIGURE 5A. ICS84325 SCHEMATIC EXAMPLE
www.icst.com/products/hiperclocks.html
8
REV. B OCTOBER 11, 2004
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