IDT / ICS 700MHZ, 3.3V LVPECL FREQUENCY SYNTHESIZER
9
ICS8432DYI-101 REV. C APRIL 10, 2007
ICS8432I-101
700MHZ, DIFFERENTIAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER
Figure 3 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
FIGURE 3. SINGLE ENDED SIGNAL DRIVING DIFFERENTIAL INPUT
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
R1
1K
C1
0.1u
R2
1K
Single Ended Clock Input
CLK
nCLK
VCC
INPUTS:
TEST_CLK INPUT:
For applications not requiring the use of the test clock, it can be
left floating. Though not required, but for additional protection, a
1k
Ω resistor can be tied from the TEST_CLK 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.