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 2004 Semtech Corp.

www.semtech.com

PROTECTION PRODUCTS

PROTECTION PRODUCTS

SM05 through SM36

Applications Information

Device Schematic & Pin Configuration

Device Connection Options

The SM series is designed to protect one bidirectional

or two unidirectional data or I/O lines operating at 5 to

36 volts. Connection options are as follows:

Bidirectional: Pin 1 is connected to the data line

and pin 2 is connected to ground (Since the device

is symmetrical, these connections may be re-

versed). The ground connection should be made

directly to a ground plane. The path length should

be kept as short as possible to minimize parasitic

inductance. Pin 3 is not connected.

Unidirectional: Data lines are connected to pin 1

and pin 2. Pin 3 is connected to ground. For best

results, this pin should be connected directly to a

ground plane on the board. The path length should

be kept as short as possible to minimize parasitic

inductance.

Circuit Board Layout Recommendations for Suppres-

sion of ESD.

Good circuit board layout is critical for the suppression

of fast rise-time transients such as ESD. The following

guidelines are recommended (Refer to application note

SI99-01 for more detailed information):

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.

Matte Tin Lead Finish

Matte tin has become the industry standard lead-free

replacement for SnPb lead finishes. A matte tin finish

is composed of 100% tin solder with large grains.

Since the solder volume on the leads is small com-

pared to the solder paste volume that is placed on the

land pattern of the PCB, the reflow profile will be

determined by the requirements of the solder paste.

Therefore, these devices are compatible with both

lead-free and SnPb assembly techniques. In addition,

unlike other lead-free compositions, matte tin does not

have any added alloys that can cause degradation of

the solder joint.

RS-232 Transceiver Protection Example