ICS841S01BGLF datasheet(10/16 Pages) IDT

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IDT™ / ICS™ PCI EXPRESS CLOCK GENERATOR

ICS841S01BG REV. B MAY 23, 2007

ICS841S01

PCI EXPRESS™ CLOCK GENERATOR

PRELIMINARY

APPLICATION INFORMATION

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, VDDA, and VDD_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 10

Ω resistor along with a 10μF and a

.01

μF bypass capacitor should be connected to each V

DDA pin.

The 10

Ω resistor can also be replaced by a ferrite bead.

FIGURE 1. POWER SUPPLY FILTERING

DDA

μF

.01

μF

3.3V

.01

μF

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.

TABLE 7. RECOMMENDED CRYSTAL SPECIFICATIONS

(

L)F

(

O)F

)

(

FIGURE 2. CRYSTAL OSCILLATOR WITH TRIM CAPACITOR

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.

XT AL_IN

XTAL_OUT

25MHz

TBD

33pF

18pF

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