ICS8745BI datasheet(14/21 Pages) RENESAS

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ICS8745BYI REVISION D JUNE 11, 2009

ICS8745BI Data Sheet

1:5 DIFFERENTIAL-TO-LVDS ZERO DELAY CLOCK GENERATOR

The following component footprints are used in this layout example.

All the resistors and capacitors are size 0603.

Power and Grounding

Place the decoupling capacitors as close as possible to the power

pins. If space allows, placement of the decoupling capacitor on the

component side is preferred. This can reduce unwanted inductance

between the decoupling capacitor and the power pin caused 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 R7, C11, and C16 should be placed as

close to the VDDA pin as possible.

Clock Traces and Termination

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 differential 50

Ω output traces should have the 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

possible, 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.

Figure 5B. PCB Board Layout for ICS8745BI

C16

GND

50 Ohm

Traces

VDDA

VDDO

VIA

Pin 1

C11

VDD

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