ICS8430-51 Datasheet, PDF (9/16 Pages) Integrated Circuit Systems – 600MHZ, LOW JITTER LVCMOS/ LVTTL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS8430-51
600MHZ, LOW JITTER
LVCMOS/ LVTTL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER
APPLICATION INFORMATION
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS8430-51 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 isolation is required. Figure 3 illustrates how
a 10Ω resistor along with a 10µF and a .01µF bypass
capacitor should be connected to each V_CCA pin.
3.3V
V_CC
.01µF 10Ω
V_CCA
.01µF
10 µF
FIGURE 3. POWER SUPPLY FILTERING
CRYSTAL INPUT AND OSCILLATOR INTERFACE
The ICS8430-51 features an internal oscillator that uses an
external quartz crystal as the source of its reference frequency.
A 16MHz crystal divided by 16 before being sent to the phase
detector provides the reference frequency. The oscillator is a
series resonant, multi-vibrator type design. This design provides
better stability and eliminates the need for large on chip capacitors.
Though a series resonant crystal is preferred, a parallel resonant
crystal can be used. A parallel resonant mode crystal used in a
series resonant circuit will exhibit a frequency of oscillation a few
hundred ppm lower than specified. A few hundred ppm translates
to KHz inaccuracy. In general computing applications this level
of inaccuracy is irrelevant. If better ppm accuracy is required, an
external capacitor can be added to a parallel resonant crystal in
series to pin 24. Figure 4A shows how to interface with a crystal.
ppm performance over various parallel resonant crystals.
Figure 4C shows the recommended tuning capacitance for
various parallel resonant crystals.
ICS8430-51
XTAL2
(Pin 25, LQFP)
XTAL1
(Pin 24, LQFP)
Figures 4A, 4B, and 4C show various crystal parameters
which are recommended only as guidelines. Figure 4A shows
how to interface a capacitor with a parallel resonant crystal.
Figure 3B shows the capacitor value needed for the optimum
Optional
FIGURE 4A. CRYSTAL INTERFACE
FIGURE 4B. Recommended tuning capacitance for various parallel FIGURE 4C. Recommended tuning capacitance for various
resonant crystals.
parallel resonant crystals.
60
14.318
50
40
15.000
16.667
30
19.440
20.000
20
10
24.000
0
14 15 16 17 18 19 20 21 22 23 24 25
Crystal Frequency (MHz)
100
80
60
40
20
0
-20 0
-40
-60
-80
-100
10
20
30
40
Series Capacitor, C1 (pF)
50
60
19.44MHz
16MHz
15.00MHz
8430AY-51
www.icst.com/products/hiperclocks.html
9
REV. D FEBRUARY 11, 2003