844003I-04 Datasheet, PDF (13/19 Pages) Integrated Device Technology – FemtoClock Crystal-to-LVDS Frequency Synthesizer

844003I-04 Datasheet
Recommendations for Unused Input and Output Pins
Inputs:
LVCMOS Control Pins
All control pins have internal pullups and 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.
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 1k resistor can be tied from
XTAL_IN 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.
LVDS Driver Termination
A general LVDS interface is shown in Figure 4. Standard termination
for LVDS type output structure requires both a 100 parallel resistor
at the receiver and a 100 differential transmission line environment.
In order to avoid any transmission line reflection issues, the 100
resistor must be placed as close to the receiver as possible. IDT
offers a full line of LVDS compliant devices with two types of output
structures: current source and voltage source. The standard
termination schematic as shown in Figure 4 can be used with either
type of output structure. If using a non-standard termination, it is
recommended to contact IDT and confirm if the output is a current
source or a voltage source type structure. In addition, since these
outputs are LVDS compatible, the amplitude and common mode
input range of the input receivers should be verified for compatibility
with the output.
LVDS Driver
100Ω
+
LVDS
Receiver
–
100Ω Differential Transmission Line
Figure 4. Typical LVDS Driver Termination
©2016 Integrated Device Technology, Inc.
13
Revision C, November 10, 2016