ICS85314AI11 datasheet(8/18 Pages) ICST

8 / 18 page

85314AGI-11

www.icst.com/products/hiperclocks.html

REV. C MAY 24, 2005

Integrated

Circuit

Systems, Inc.

ICS85314I-11

LOW SKEW, 1-TO-5

DIFFERENTIAL-TO-2.5V/3.3V LVPECL FANOUT BUFFER

APPLICATION INFORMATION

FIGURE 2. SINGLE ENDED SIGNAL DRIVING DIFFERENTIAL INPUT

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

WIRING THE DIFFERENTIAL INPUT TO ACCEPT SINGLE ENDED LEVELS

ratio 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.

V_REF

0.1u

Single Ended Clock Input

CLK

nCLK

VCC

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:

LVPECL OUTPUT

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.

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