8431AMI-21

www.icst.com/products/hiperclocks.html

REV. A AUGUST 2, 2005

11

Integrated

Circuit

Systems, Inc.

ICS8431I-21

TO

The following component footprints are used in this layout

example:

All the resistors and capacitors are size 0603.

Place the decoupling capacitors C1, C2 and C6, as close as

possible to the power pins. If space allows, placment of the

decoupling capacitor on the component side is preferred. This

can reduce unwanted inductance between the decoupling ca-

pacitor and the power pin generated by the via.

Maximize the power and ground pad sizes and number of vias

capacitors. This can reduce the inductance between the power

and ground planes and the component power and ground pins.

The RC filter consisting of R5, C3, and C4 should be placed as

close to the V

Poor signal integrity can degrade the system performance or

cause system failure. In synchronous high-speed digital systems,

the clock signal is less tolerant to poor signal integrity than other

signals. Any ringing on the rising or falling edge or excessive ring

back can cause system failure. The shape of the trace and the

trace delay might be restricted by the available space on the board

and the component location. While routing the traces, the clock

signal traces should be routed first and should be locked prior to

routing other signal traces.

• The 50

Ω output trace pair should have same length.

• Avoid sharp angles on the clock trace. Sharp angle turns

cause the characteristic impedance to change on the

transmission lines.

• Keep the clock traces on the same layer. Whenever pos-

sible, avoid placing vias on the clock traces. Placement

of vias on the traces can affect the trace characteristic

impedance and hence degrade signal integrity.

• To prevent cross talk, avoid routing other signal traces in

parallel with the clock traces. If running parallel traces is

unavoidable, allow a separation of at least three trace

widths between the differential clock trace and the other

signal trace.

• Make sure no other signal traces are routed between the

clock trace pair.

• The matching termination resistors should be located as

close to the receiver input pins as possible.

The matching termination resistors R1, R2, R3 and R4 should

be located as close to the receiver input pins as possible.

Other termination scheme can also be used but is not shown

in the example.

The crystal X1 should be located as close as possible to the pins

25 (XTAL_OUT) and 26 (XTAL_IN).The trace length between the

X1 and U1 should be kept to a minimum to avoid unwanted para-

sitic inductance and capacitance. Other signal traces should not

be routed near the crystal traces.

C4

Signals

X1

C3

VCC

GND

VIA

C1

Zo=50 Ohm

U1

Zo=50 Ohm

C2

C8

R5

C6

ICS8431-21

C7