ICS813001I Datasheet, PDF (12/18 Pages) Integrated Circuit Systems – DUAL VCXO W/3.3V, 2.5V LVPECL FEMTOCLOCK-TM PLL

Integrated
Circuit
Systems, Inc.
ICS813001I
DUAL VCXO W/3.3V, 2.5V LVPECL
FEMTOCLOCK™ PLL
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:
LVPECL OUTPUT
All unused LVPECL outputs can be left floating. We
recommend that there is no trace attached. Both sides of the
differential output pair should either be left floating or
terminated.
CLK INPUT:
For applications not requiring the use of a clock input, it can
be left floating. Though not required, but for additional
protection, a 1kΩ resistor can be tied from the CLK input to
ground.
CLK/nCLK INPUT:
For applications not requiring the use of the differential input,
both CLK and nCLK can be left floating. Though not required,
but for additional protection, a 1kΩ resistor can be tied from
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.
VC input pin - do not float, must be biased.
TERMINATION FOR 3.3V LVPECL OUTPUT
The clock layout topology shown below is a typical ter-
mination for LVPECL outputs. The two different layouts
mentioned are recommended only as guidelines.
FOUT and nFOUT are low impedance follower outputs
that generate ECL/LVPECL compatible outputs. There-
fore, terminating resistors (DC current path to ground)
or current sources must be used for functionality. These
outputs are designed to drive 50Ω transmission lines.
Matched impedance techniques should be used to maxi-
mize operating frequency and minimize signal distor-
tion. Figures 5A and 5B show two different layouts which
are recommended only as guidelines. Other suitable
clock layouts may exist and it would be recommended
that the board designers simulate to guarantee compat-
ibility across all printed circuit and clock component pro-
cess variations.
Z_o = 50Ω
FOUT
FIN
Z_o = 50Ω
50Ω
RTT =
1
((V_OH + V_OL) / (V_CC – 2)) – 2
Z_o
50Ω
V_CC - 2V
RTT
FOUT
3.3V
125Ω
125Ω
Z_o = 50Ω
FIN
Z_o = 50Ω
84Ω
84Ω
FIGURE 5A. LVPECL OUTPUT TERMINATION
FIGURE 5B. LVPECL OUTPUT TERMINATION
813001AGI
www.icst.com/products/hiperclocks.html
REV. A SEPTEMBER 2, 2005
12