
87951AYI
www.idt.com
REV. C JULY 17, 2010
9
ICS87951I
LOW SKEW, 1-TO-9
DIFFERENTIAL-TO-LVCMOS/LVTTL ZERO DELAY BUFFER
FIGURE 3C. CLK/NCLK INPUT DRIVEN BY
3.3V LVPECL DRIVER
FIGURE 3B. CLK/NCLK INPUT DRIVEN BY
3.3V LVPECL DRIVER
FIGURE 3D. CLK/NCLK INPUT DRIVEN BY
3.3V LVDS DRIVER
3.3V
R1
50
R3
50
Zo = 50 Ohm
LVPECL
Zo = 50 Ohm
HiPerClockS
CLK
nCLK
3.3V
Input
R2
50
Zo = 50 Ohm
Input
HiPerClockS
CLK
nCLK
3.3V
R3
125
R2
84
Zo = 50 Ohm
3.3V
R4
125
LVPECL
R1
84
3.3V
DIFFERENTIAL CLOCK INPUT INTERFACE
The CLK1 /nCLK1 accepts LVDS, LVPECL, LVHSTL, SSTL,
HCSL and other differential signals. Both V
SWING and VOH must
meet the V
PP and VCMR input requirements. Figures 4A to 4D show
interface examples for the CLK1/nCLK1 input driven by the
most common driver types. The input interfaces suggested
FIGURE 3A. CLK/NCLK INPUT DRIVEN BY
LVHSTL DRIVER
here are examples only. Please consult with the vendor of the
driver component to confirm the driver termination requirements.
For example in
Figure 3A, the input termination applies for
LVHSTL drivers. If you are using an LVHSTL driver from
another vendor, use their termination recommendation.
1.8V
R2
50
Input
LVHSTL Driver
ICS
HiPerClockS
R1
50
LVHSTL
3.3V
Zo = 50 Ohm
HiPerClockS
CLK
nCLK
Zo = 50 Ohm
R1
100
3.3V
LVDS_Driv er
Zo = 50 Ohm
Receiv er
CLK
nCLK
3.3V
INPUTS:
CLK INPUT:
For applications not requiring the use of a clock input, it can
be left floating. Though not required, but for additional
protection, a 1k
Ω resistor can be tied from the CLK input to
ground.
CLK/nCLK INPUT:
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 1k
Ω resistor can be tied from
CLK 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 1k
Ω resistor can be used.
RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS
OUTPUTS:
LVCMOS OUTPUT:
All unused LVCMOS output can be left floating. We
recommend that there is no trace attached.