9©2016 Integrated Device Technology, Inc. Revision B, January 20, 2016
843252 Datasheet
Application Information
Recommendations for Unused Input Pins
Inputs:
LVCMOS Control Pins
All control pins have internal pullups and pulldowns; additional
resistance is not required but can be added for additional protection.
A 1k 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.
Power Supply Filtering Technique
As in any high speed analog circuitry, the power supply pins are
vulnerable to random noise. To achieve optimum jitter per- formance,
power supply isolation is required. The 843252 provides separate
power supplies to isolate any high switching noise from the outputs to
the internal PLL. V
CC,
V
CCA,
V
CCO_A,
and V
CCO_B
should be
individually connected to the power supply plane through vias, and
0.01µF 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 additional 10 resistor along with a 10F bypass
capacitor be connected to the V
CCA
pin.
Figure 1. Power Supply Filtering
Crystal Input Interface
The 843252 has been characterized with 18pF parallel resonant
crystals. The capacitor values, C1 and C2, shown in Figure 2 below
were determined using a 25MHz, 18pF parallel resonant crystal and
were chosen to minimize the ppm error.
Figure 2. Crystal Input Interface
V
CC
V
CCA
3.3V
10µF0.01µF
0.01µF
XTAL_IN
XTAL_OUT
X1
18pF Parallel Crystal
C1
22pF
C2
22pF
