ICS84324 Datasheet, PDF (8/14 Pages) Integrated Circuit Systems – CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER WITH FANOUT BUFFER

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS84324
CRYSTAL-TO-3.3V LVPECL
FREQUENCY SYNTHESIZER WITH FANOUT BUFFER
CRYSTAL INPUT INTERFACE
A crystal can be characterized for either series or parallel mode
operation. The ICS84324 has a built-in crystal oscillator circuit.
This interface can accept either a series or parallel crystal without
additional components and generate frequencies with accuracy
suitable for most applications. Additional accuracy can be
achieved by adding two small capacitors C1 and C2 as shown in
Figure 4.
25MHz X1
19
C1
18pF
XTAL2
20
C2
22pF
XTAL1
ICS84324
Figure 4. CRYSTAL INPUt INTERFACE
SCHEMATIC EXAMPLE
Figure 5A shows a schematic example of using an ICS84324. In
this example, the input is a 25MHz parallel resonant crystal with
load capacitor CL=18pF. The frequency fine tuning capacitors
C1 and C2 is 22pF and 18pF respectively. This example also
shows logic control input handling. The configuration is set at
F_SEL[1:0]=11 therefore the output frequency is 125MHz. It is
recommended to have one decouple capacitor per power pin.
Each decoupling capacitor should be located as close as pos-
sible to the power pin. The low pass filter R7, C11 and C16 for
clean analog supply should also be located as close to the V_CCA
pin as possible.
VCC
VCC
R7
24
C 11
0.1u
C16
10u
VCC
VCCA
22p
C1
X1
25MHz,18pF
C2
18p
R4 VCC
1K
F_SEL1
R5 F_SEL0
1K
U2
13
14
15
16
VC C O
VEE
PLL_SEL
17
18
19
20
VC C
VC C A
VEE
XTAL2
21 ^XTAL1
22
23
24
MR
F_SEL1
F_SEL0
VC C O
I C S84324
nQ5
Q5
nQ4
Q4
nQ3
Q3
12
11
10
9
8
7
6
nQ2 ₅
Q2 ₄
nQ1
Q1
nQ0
Q0
3
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
84324EM
FIGURE 5A. ICS84324 SCHEMATIC EXAMPLE
www.icst.com/products/hiperclocks.html
8
REV. A SEPTEMBER 18, 2003