ICS841S01 Datasheet, PDF (10/16 Pages) Integrated Device Technology – PCI EXPRESS™ CLOCK GENERATOR

ICS841S01
PCI EXPRESS™ CLOCK GENERATOR
APPLICATION INFORMATION
PRELIMINARY
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins are
vulnerable to random noise. The ICS841S01 provides separate
power supplies to isolate any high switching noise from the out-
puts to the internal PLL. V_{DD_REF}, V_DDA, and V_{DD_SRC} should be indi-
vidually connected to the power supply plane through vias, and
bypass capacitors should be used for each pin. To achieve opti-
mum jitter performance, power supply isolation is required. Fig-
ure 1 illustrates how a 10Ω resistor along with a 10μF and a
.01μF
bypass
capacitor
should
be
connected
to
each
V
DDA
pin.
The 10Ω resistor can also be replaced by a ferrite bead.
3.3V
V
DD
.01μF 10Ω
V_DDA
.01μF
10μF
FIGURE 1. POWER SUPPLY FILTERING
USING THE ON-BOARD CRYSTAL OSCILLATOR
The ICS841S01 features a fully integrated Pierce oscillator to
minimize system implementation costs. The ICS841S02I may be
operated with a 25MHz crystal and without additional components.
Recommended operation for the crystal should be of a parallel
resonant type and a load specification of C_L = 18pF. See Table 7
for complete crystal specifications.
If more precise frequency control is desired, the addition of
capacitors from each of the XTAL_IN and XTAL_OUT pins to
ground may be used to trim the frequency as shown in Figure 2.
The crystal and optional trim capacitors should be located as
close to the ICS841S01 XTAL_IN and XTAL_OUT pins as possible
to avoid any board level parasitic.
25 MHz
T3B3pDF
XT AL_IN
TABLE 7. RECOMMENDED CRYSTAL SPECIFICATIONS
Parameter
Value
Crystal Cut
Fundamental AT Cut
Resonance
Parallel Resonance
Shunt Capacitance (C_L)
Load Capacitance (C_O)
Equivalent Series Resistance (ESR)
5-7pF
18pF
20-50Ω
T1B8pDF
XTAL_OUT
FIGURE 2. CRYSTAL OSCILLATOR WITH TRIM CAPACITOR
IDT^™ / ICS^™ PCI EXPRESS CLOCK GENERATOR
10
ICS841S01BG REV. B MAY 23, 2007