843204I-01 Datasheet, PDF (8/14 Pages) Integrated Device Technology – FemtoClock® Crystal-to-3.3V LVPECL Frequency Synthesizer

843204I-01 DATA SHEET
RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS
INPUTS:
OUTPUTS:
CRYSTAL INPUTS
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.
LVPECL OUTPUTS
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 INPUTS
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.
TERMINATION FOR 3.3V LVPECL OUTPUT
The clock layout topology shown below is a typical termination for
LVPECL outputs. The two different layouts mentioned are recom-
mended only as guidelines.
FOUT and nFOUT are low impedance follower outputs that generate
ECL/LVPECL compatible outputs. Therefore, 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 maximize
operating frequency and minimize signal distortion. 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
compatibility across all printed circuit and clock component process
variations.
FIGURE 5A. LVPECL OUTPUT TERMINATION
FEMTOCLOCKS™ CRYSTAL-TO-
3.3V LVPECL FREQUENCY SYNTHESIZER
FIGURE 5B. LVPECL OUTPUT TERMINATION
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REVISION A 11/5/15