
IDT / ICS HCSL CLOCK GENERATOR
8
ICS841602AGI REV. A JULY 10, 2008
ICS841602I
FEMTOCLOCKS CRYSTAL-TO-HCSL CLOCK GENERATOR
APPLICATION INFORMATION
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. To achieve optimum jitter
performance, power supply isolation is required. The ICS841602I
provides separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V
DD and VDDA
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
DD pin and also shows
that V
DDA requires that an additional10Ω resistor along with a
10F bypass capacitor be connected to the V
DDA pin.
POWER SUPPLY FILTERING TECHNIQUES
FIGURE 1. POWER SUPPLY FILTERING
10
Ω
V
DDA
10
μF
.01
μF
3.3V
.01
μF
V
DD
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.
REF_IN INPUT
For applications not requiring the use of the reference clock,
it can be left floating. Though not required, but for additional
protection, a 1k
Ω resistor can be tied from the REF_IN to ground.
LVCMOS CONTROL PINS
All control pins have internal 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:
DIFFERENTIAL OUTPUTs
All unused differential 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.