8421002I-01 Datasheet, PDF (8/15 Pages) Integrated Device Technology – FemtoClock Crystal-to-HSTL Frequency Synthesizer

8421002I-01 DATA SHEET
APPLICATION INFORMATION
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply
pins are vulnerable to random noise. The 8421002I-01 pro-
vides separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V , V , and
DD
DDA
V should be individually connected to the power supply
DDO
plane through vias, and bypass capacitors should be
used for each pin. To achieve optimum jitter performance,
power supply isolation is required. Figure 1 illustrates how
a 10Ω resistor along with a 10µF and a .01μF bypass
capacitor should be connected to each V .
DDA
3.3V or 2.5V
V
DD
.01μF 10Ω
V
DDA
.01μF
10μF
FIGURE 1. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
The 8421002I-01 has been characterized with 18pF parallel
resonant crystals. The capacitor values 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
RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS
INPUTS:
OUTPUTS:
CRYSTAL INPUT:
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 1kΩ resistor can be tied
from XTAL_IN to ground.
HSTL OUTPUT
All unused HSTL 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.
REF_CLK INPUT:
For applications not requiring the use of the reference clock,
it can be left floating. Though not required, but for additional
protection, a 1kΩ resistor can be tied from the REF_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 1kΩ resistor can be used.
FEMTOCLOCKS™ CRYSTAL-TO-HSTL
8
FREQUENCY SYNTHESIZER
REVISION B 8/14/15