IDT / ICS 3.3V LVPECL FREQUENCY SYNTHESIZER
7
ICS843204AGI REV. A MARCH 18, 2009
ICS843204I
FEMTOCLOCK CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER
APPLICATION INFORMATION
As in any high speed analog circuitry, the power supply pins are
vulnerable to random noise. To achieve optimum jitter perfor-
mance, power supply isolation is required. The ICS843204I pro-
vides separate power supplies to isolate any high switching noise
from the outputs to the internal PLL. V
CC, VCCA_A, VCCA_B, VCCO_A
and V
CCO_B should be individually connected to the power supply
plane through vias, and 0.01F bypass capacitors should be used
for each pin.
Figure 1 illustrates this for a generic V
CC pin and
also shows that V
CCA requires that an additional10Ω resistor
along with a 10F bypass capacitor be connected to the V
CCA
pin.
POWER SUPPLY FILTERING TECHNIQUES
FIGURE 1. POWER SUPPLY FILTERING
VCC
VCCA_A
VCCA_B
3.3V
10
Ω
10
Ω
10F
.01F
10F
.01F
INPUTS:
CRYSTAL INPUTS
For applications not requiring the use of the crystal oscillator input,
both XTAL_IN and XTAL_OUT can be left floating. Though not
required, but for additional protection, a 1k
Ω resistor can be tied
from XTAL_IN to ground.
CLK INPUTS
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.
LVCMOS CONTROL PINS
All control pins have internal pullups or pulldowns; 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 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.