ICS8535-21 Datasheet, PDF (8/14 Pages) Integrated Circuit Systems – LOW SKEW, 1-TO-2 LVCMOS/LVTTL-TO-3.3V LVPECL FANOUT BUFFER

Integrated
Circuit
Systems, Inc.
ICS8535-21
LOW SKEW, 1-TO-2
LVCMOS/LVTTL-TO-3.3V LVPECL FANOUT BUFFER
APPLICATION INFORMATION
TERMINATION FOR LVPECL OUTPUTS
The clock layout topology shown below is a typical termina-
tion 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. Therefore, termi-
nating 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 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.
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 2A. LVPECL OUTPUT TERMINATION
FIGURE 2B. LVPECL OUTPUT TERMINATION
8535AG-21
www.icst.com/products/hiperclocks.html
8
REV. A OCTOBER 20, 2004