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 2005 Semtech Corp.

www.semtech.com

PROTECTION PRODUCTS

LCDA05 through LCDA24

Applications Information

Device Connection for Protection of Two High-Speed

Data Lines

The LCDAxx is designed to protect up to two high-speed

data lines. The LCDAxx utilizes a low capacitance

compensation diode in series with, but in opposite

polarity to a TVS diode in each line. The resulting

capacitance is less than 5pF per line. Each line will

only suppress transient events in one polarity. There-

fore, to achieve protection in both positive and nega-

tive polarity, a second TVS/rectifier pair is connected in

anti-parallel to the first. Pins 1, 2, 7, and 8 are used to

protect one data line. Pins 3, 4, 5, and 6 are used to

protect the second data line.

The device is connected as follows:

Pins 1 and 2 are tied together and pins 7 and 8 are

tied together providing the protection circuit for

one I/O line. Pins 3 and 4 are tied together and

pins 5 and 6 are tied together providing the protec-

tion circuit for the second I/O line. Since the

device is electrically symmetrical, either side of the

connected pairs may be used to protect the lines.

The other side of the pair is used to make the

ground connection. The ground connections should

be made directly to the ground plane for best

results. The path length is kept as short as pos-

sible to reduce the effects of parasitic inductance

in the board traces.

Circuit Board Layout Recommendations for Suppres-

sion of ESD.

Good circuit board layout is critical for the suppression

of ESD induced transients. The following guidelines are

recommended:

Place the TVS near the input terminals or connec-

tors to restrict transient coupling.

Minimize the path length between the TVS and the

protected line.

Minimize all conductive loops including power and

ground loops.

The ESD transient return path to ground should be

kept as short as possible.

Never run critical signals near board edges.

Use ground planes whenever possible.

1

2

3

45

6

7

8

Line 1

In/Out

Line 1

Ground

Line 2

In/Out

Line 2

Ground

From Connector

To Protected

Device

1

2

3

45

6

7

8

Line 1

In/Out

Ground

Line 2

In/Out

From Connector

To Protected

Device

Connection Options

I/O Line Protection

LCDA Connection Diagram

I/O 1

I/O 2

I/O 1

I/O 2

1

2

3

45

6

7

8