Rainbow-electronics SCAN92LV090 Instrukcja Użytkownika Pobierz pdf (Strona 7)

Applications Information

General application guidelines and hints may be found in the

following application notes: AN-808, AN-1108, AN-977,

AN-971, and AN-903.

There are a few common practices which should be implied

when designing PCB for Bus LVDS signaling. Recom-

mended practices are:

•

Use at least 4 PCB board layer (Bus LVDS signals,

ground, power and TTL signals).

•

Keep drivers and receivers as close to the (Bus LVDS

port side) connector as possible.

•

Bypass each Bus LVDS device and also use distributed

bulk capacitance between power planes. Surface mount

capacitors placed close to power and ground pins work

best. Two or three high frequency, multi-layer ceramic

(MLC) surface mount (0.1 µF, 0.01 µF, 0.001 µF) in

parallel should be used between each V

and ground.

The capacitors should be as close as possible to the V

pin.

Multiple vias should be used to connect V

and Ground

planes to the pads of the by-pass capacitors.

In addition, randomly distributed by-pass capacitors

should be used.

•

Use the termination resistor which best matches the dif-

ferential impedance of your transmission line.

•

Leave unused Bus LVDS receiver inputs open (floating).

Limit traces on unused inputs to

0.5 inches.

•

Isolate TTL signals from Bus LVDS signals

MEDIA (CONNECTOR or BACKPLANE) SELECTION:

•

Use controlled impedance media. The backplane and

connectors should have a matched differential imped-

ance.

TABLE 1. Functional Table

MODE SELECTED DE RE

DRIVER MODE H H

RECEIVER MODE L L

TRI-STATE MODE L H

LOOP BACK MODE H L

TABLE 2. Transmitter Mode

INPUTS OUTPUTS

DE D

DO+ DO−

HL LH

HH HL

H 0.8V

2.0V X X

LXZZ

TABLE 3. Receiver Mode

INPUTS OUTPUT

(RI+) – (RI−)

LL(

−100 mV) L

LH(

+100 mV) H

L −100 mV

+100 mV

HX Z

X = High or Low logic state

L = Low state

Z = High impedance state

H = High state

Test Circuits and Timing Waveforms

10124203

FIGURE 1. Differential Driver DC Test Circuit

SCAN92LV090

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