ics8535-21 Integrated Device Technology, ics8535-21 Datasheet - Page 8

• Manufacturer Part Number: ics8535-21
• Description: Low Skew, 1-to-2 Lvcmos/lvttl-to-3.3v Lvpecl Fanout Buffer
• Manufacturer: Integrated Device Technology

Application Information
Recommendations for Unused Input and Output Pins
Inputs:
CLK Inputs
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.
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 Outputs
The clock layout topology shown below is a typical termination for
LVPECL outputs. The two different layouts mentioned are
recommended only as guidelines.
FOUT and FOUT 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
Figure 2A. 3.3V LVPECL Output Termination
IDT™ / ICS™ 3.3V LVPECL FANOUT BUFFER
ICS8535-21
LOW SKEW, 1-TO-2 LVCMOS/LVTTL-TO-3.3V LVPECL FANOUT BUFFER
RTT =
((V
FOUT
OH
+ V
OL
) / (V
1
CC
Z
Z
– 2)) – 2
o
o
= 50Ω
= 50Ω
Z
o
50Ω
RTT
50Ω
V
CC
FIN
- 2V
8
Outputs:
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.
transmission lines. Matched impedance techniques should be
used to maximize operating frequency and minimize signal
distortion. Figures 2A and 2B 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 2B. 3.3V LVPECL Output Termination
FOUT
ICS8535AG-21 REV. A FEBRUARY 24, 2009
Z
Z
o
o
= 50Ω
= 50Ω
125Ω
84Ω
3.3V
125Ω
84Ω
FIN