ICS843246I Datasheet, PDF (8/17 Pages) Integrated Device Technology – FEMTOCLOCKS™ CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER W/INTEGRATED FANOUT BUFFER

ICS843246I
FEMTOCLOCKS™ CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER W/FANOUT BUFFER
APPLICATION INFORMATION
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS843246I provides
separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V_CC, V_CCA and
V_CCO should be individually connected to the power supply plane
through vias, and bypass capacitors should be used for each
pin. To achieve optimum jitter performance, power supply iso-
lation is required. Figure 1 illustrates how a 10Ω resistor along
with a 10μF and a .01μF bypass capacitor should be connected
to each V_CCA pin.
V_CC
V_CCA
3.3V
.01μF 10Ω
.01μF
10μF
FIGURE 1. POWER SUPPLY FILTERING
RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS
INPUTS:
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 1kΩ resistor can be used.
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.
CRYSTAL INPUT INTERFACE
The ICS843246I has been characterized with 18pF parallel
resonant crystals. The capacitor values shown in Figure 2
below were determined using an 18pF parallel resonant
crystal and were chosen to minimize the ppm error.
X1
18pF Parallel Crystal
XTAL_OUT
C1
22p
XTAL_IN
C2
22p
FIGURE 2. CRYSTAL INPUt INTERFACE
IDT^™ / ICS^™ 3.3V LVPECL FREQUENCY SYNTHESIZER
8
ICS843246BGI REV. A AUGUST 2, 2007