ICS840004-01 Datasheet, PDF (10/13 Pages) Integrated Circuit Systems – FEMTOCLOCKS™ CRYSTAL-TO LVCMOS/LVTTL FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS840004-01
FEMTOCLOCKS™ CRYSTAL-TO-
LVCMOS/LVTTL FREQUENCY SYNTHESIZER
RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS
INPUTS:
CRYSTAL INPUT:
For applications not requiring the use of the crystal oscillator
input, both XTAL_IN and XTAL_OUT can be left floating.
Though not required, but for additional protection, a 1kΩ
resistor can be tied from XTAL_IN to ground.
OUTPUTS:
LVCMOS OUTPUT:
All unused LVCMOS output can be left floating. We
recommend that there is no trace attached.
TEST_CLK INPUT:
For applications not requiring the use of the test clock, it can
be left floating. Though not required, but for additional
protection, a 1kΩ resistor can be tied from the TEST_CLK to
ground.
LVCMOS CONTROL PINS:
All control pins have internal pull-ups or pull-downs; additional
resistance is not required but can be added for additional
protection. A 1kΩ resistor can be used.
LAYOUT GUIDELINE
Figure 3 shows a schematic example of the ICS840004-01. An
example of LVCMOS termination is shown in this schematic.
Additional LVCMOS termination approaches are shown in the
LVCMOS Termination Application Note. In this example, an 18pF
parallel resonant 25MHz crystal is used. The C1=22pF and
C2=22pF are recommended for frequency accuracy. For dif-
ferent board layout, the C1 and C2 may be slightly adjusted
for optimizing frequency accuracy. 1KΩ pullup or pulldown
resistors can be used for the logic control input pins.
Logic Control Input Examples
Set Logic
3.3V _{Input to}
'1'
RU1
1K
To Logic
Input
pins
RD1
Not Install
Set Logic
3.3V _{Input to}
'0'
RU2
Not Install
To Logic
Input
pins
RD2
1K
3.3V
VDDA
R2
C3
10 10uF
C4
0.01u
3.3V
C6
0.1u
U1
1
2 ^F_SEL0
3
4
nc
nXTAL_SEL
5 ^TEST_CLK
6 ^OE
7
8
9
MR
nPLL_SEL
VDDA
10 ^nc
VDD
I C S840004-01
C2
22pF
20
F_SEL1 ₁₉
GND
Q0
18
17
Q1 ₁₆
VDDO ₁₅
Q2
Q3
GND
14
13
12
XTAL_IN ₁₁
XTAL_OUT
XTAL_OUT
X1
XTAL_I N
C1
22pF
R3
36
Zo = 50 Ohm
LVCMOS
3.3V
R4
36
Zo = 50 Ohm
C5
0. 1u
LVCMOS
8400042AG-01
FIGURE 3. ICS840004-01 SCHEMATIC EXAMPLE
www.icst.com/products/hiperclocks.html
10
REV. B JANUARY 3, 2006