IDT
™
/ ICS
™
1-TO-9, 2.5V, 3.3V LVPECL/ECL FANOUT BUFFER 9 ICS853031AY REV. C AUGUST 12, 2008
ICS853031
LOW SKEW, 1-TO-9, DIFFERENTIAL-TO-2.5, 3.3V LVPECL/ECL FANOUT BUFFER
APPLICATION INFORMATION
Figure 2
shows how the differential input can be wired to accept
single ended levels. The reference voltage V_REF ~ V
CC
/2 is
generated by the bias resistors R1, R2 and C1. This bias circuit
should be located as close as possible to the input pin. The ratio
FIGURE 2. SINGLE ENDED SIGNAL DRIVING DIFFERENTIAL INPUT
WIRING THE DIFFERENTIAL INPUT TO ACCEPT SINGLE ENDED LEVELS
of R1 and R2 might need to be adjusted to position the V_REF in
the center of the input voltage swing. For example, if the input
clock swing is only 2.5V and V
CC
= 3.3V, V_REF should be 1.25V
and R2/R1 = 0.609.
R2
1K
V
CC
CLK_IN
+
-
R1
1K
C1
0.1uF
V_REF
INPUTS:
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.
PCLK/nPCLK INPUTS
For applications not requiring the use of a differential input, both
the PCLK and nPCLK pins can be left floating. Though not
required, but for additional protection, a 1kΩ resistor can be tied
from PCLK to ground.
LVCMOS CONTROL PINS
All control pins have internal pullups or pulldowns; additional
resistance is not required but can be added for additional
protection. A 1kΩ resistor can be used.
RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS
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.
