
ICS844004-104
FEMTOCLOCKCRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER
IDT / ICS LVDS FREQUENCY SYNTHESIZER
10
ICS844004AK-104 REV. A SEPTEMBER 15, 2008
Recommendations for Unused Input and Output Pins
Inputs:
LVCMOS Control Pins
All control pins have internal pulldowns; additional resistance is not
required but can be added for additional protection. A 1k
resistor
can be used.
REF_CLK INPUT
For applications not requiring the use of the reference clock,
it can be left floating. Though not required, but for additional
protection, a 1k
resistor can be tied from the REF_CLK to
ground.
Outputs:
LVDS Outputs
All unused LVDS output pairs can be either left floating or
terminated with 100
across. If they are left floating, we
recommend that there is no trace attached.
3.3V, 2.5V LVDS Driver Termination
A general LVDS interface is shown in Figure 4. In a 100
differential transmission line environment, LVDS drivers require a
matched load termination of 100
across near the receiver input.
For a multiple LVDS outputs buffer, if only partial outputs are used,
it is recommended to terminate the unused outputs.
Figure 4. Typical LVDS Driver Termination
LVDS Driver
R1
100
–
+
50
50
3.3V or 2.5V
V
DD
100
Differential Transmission Line