SM712.TCT

更新时间： 2024-01-13 13:55:32

品牌	Logo	应用领域
商升特 - SEMTECH		二极管电视
页数	文件大小	规格书
6页	147K
描述
Asymmetrical TVS Diode for Extended Common-Mode RS-485

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SM712.TCT 数据手册

SM712

PROTECTION PRODUCTS

Applications Information

RS-485 Common Mode Voltages

Device Connection for Protection of Two RS-485 Data

Lines

EIA RS-485 specifies a ±7V ground difference between

devices on the bus. This permits the bus voltage to

range from +12V (5V + 7V) to -7V (0 - 7V).

The SM712 is designed to protect two RS-485 data

lines in extended common mode applications. The

SM712 may be used to protect devices from transient

voltages resulting from ESD, EFT, and lightning. The

device is designed with asymmetrical operating volt-

ages for optimum protection. The TVS diodes at pins 1

and 2 have a working voltage of 12 volts. These pins

are connected to the differential data line pairs. The

TVS diodes at pin 3 have a working voltage of 7 volts.

Pin 3 is connected to ground. The internal TVS diodes

of the SM712 will protect the transceiver input from

positive transient voltage spikes greater than 12V and

negative spikes greater than 7V.

RS-485 Protection Circuit

A series current limiting resistor may be added in

applications requiring enhanced surge immunity.

Circuit Board Layout Recommendations.

Good circuit board layout is critical for the suppression

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

guidelines are recommended:

Place the SM712 near the input terminals or

connectors to restrict electromagnetic coupling.

Minimize the path length between the SM712 and

the protected line. This minimizes voltage over-

shoot due to parasitic inductance of board traces.

Use ground planes whenever possible.

Long, single trace ground conductors should be

avoided. The ground pin (Pin 3) should be con-

nected directly to a ground plane on the circuit

board for best results.

Minimize all conductive loops including power and

ground loops.

Never run critical signals near board edges.

www.semtech.com

2004 Semtech Corp.

1 2 345 6

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