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| Asymmetrical TVS Diode for Extended Common-Mode RS-485 PROTECTION PRODUCTS Description The SM712 transient voltage suppressor (TVS) diode is designed for asymmetrical (12V to -7V ) protection in multi-point data transmission standard RS-485 applications. The SM712 may be used to protect devices from transient voltages resulting from electrostatic discharge (ESD), electrical fast transients (EFT), and lightning. The SM712 features 400 Watts (tp = 8/20s) of power handling capability to accommodate the higher transient voltage levels which may be expected in extended common mode applications. This provides higher equipment reliability and eliminates the guess work required when using zener diodes that are not rated to handle such transient conditions. The SM712 replaces four discrete components by integrating two 12V and two 7V TVS diodes in a single package. The integrated design aids in reducing voltage over-shoot associated with trace inductance. The low clamping voltage of the SM712 minimizes the stress on the protected transceiver. The SOT23 package allows flexibility in the design of crowded circuit boards. SM712 Features u 400 watts peak pulse power (tp = 8/20s) u Transient protection for asymmetrical data lines to IEC 61000-4-2 (ESD) 15kV (air), 8kV (contact) IEC 61000-4-4 (EFT) 40A (t5/50ns) IEC 61000-4-5 (Lightning) 12A (8/20s) Protects two +12V to -7V lines Low capacitance Low clamping voltage Solid-state silicon avalanche technology u u u u Mechanical Characteristics u u u u JEDEC SOT23 package Molding compound flammability rating: UL 94V-0 Marking : 712 Packaging : Tape and Reel per EIA 481 Applications u Protection of RS-485 transceivers with extended u u u u common-mode range Security systems Automatic Teller Machines HFC systems Networks Circuit Diagram Schematic & PIN Configuration SOT23 (Top View) Revision 9/2000 1 www.semtech.com SM712 PROTECTION PRODUCTS Absolute Maximum Rating R ating Peak Pulse Pow er (tp = 8/20 s) Peak Pulse Current (tp = 8/20 s) Lead Sold ering Temp erature Op erating Temp erature Storage Temp erature Symbo l Pp k I PP TL TJ TSTG Value 400 17 260 (10 sec.) -55 to +125 -55 to +150 Units Watts A C C C Electrical Characteristics SM712 Pins 1 to 3 and 2 to 3 (12V T VS) Par ame te r Reverse Stand -Off Voltage Reverse Breakd ow n Voltage Reverse Leakage Current Clamp ing Voltage Clamp ing Voltage Junction Cap acitance Symbo l V RWM V BR IR VC VC Cj Co nd itio ns Pin 3 to 1 or Pin 2 to 1 IPT = 1mA VR = V RWM IPP = 5A , tp = 8/20 s IPP = 17A , tp = 8/20 s VR = 0V, f = 1MHz V R = V RWM, f = 1MHz 45 13.3 1 20 26 75 45 MI N T YP MA X 12 7.5 20 10 12 75 pF Pins 3 to 1 and 3 to 2 (7V T VS) MI N T YP MA X 7 Units V V nA V V a 2000 Semtech Corp. 2 www.semtech.com SM712 PROTECTION PRODUCTS Typical Characteristics Non-Repetitive Peak Pulse Power vs. Pulse Time 10 Peak Pulse Power - PPP (kW) 110 100 % of Rated Power or IPP 90 80 70 60 50 40 30 20 10 0.01 0.1 1 10 Pulse Duration - tp ( s) 100 1000 0 0 25 50 75 100 125 150 175 Ambient Temperature - TA (oC) Power Derating Curve 1 0.1 Pulse Waveform 110 100 90 80 Percent of IPP 70 60 50 40 30 20 10 0 0 5 10 15 Time (s) 20 25 30 td = IPP/2 e -t Clamping Voltage vs. Peak Pulse Current 24 Clamping Voltage - V C (V) Waveform Parameters: tr = 8s td = 20s 22 20 18 16 14 12 10 8 6 4 2 0 0 2 4 6 8 10 12 14 16 Peak Pulse Current - IPP (A) Pin 3 to 1 & 3 to 2 Pin 1 to 3 & 2 to 3 Capacitance vs. Reverse Voltage 80 70 60 Capacitance (pF) 50 40 30 20 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Reverse Voltage (V) a 2000 Semtech Corp. 3 www.semtech.com SM712 PROTECTION PRODUCTS Applications Information 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 voltages for optimum protection. The TVS diodes at pins 1 & 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. 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: l l RS-485 Common Mode Voltages RS-485 Protection Circuit l l l l 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 overshoot 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 connected 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. a 2000 Semtech Corp. 4 www.semtech.com SM712 PROTECTION PRODUCTS Outline Drawing - SOT23 Land Pattern - SOT23 Note 1 : Grid placement courtyard is 8 x 8 elements (4mm x 4mm) in accordance with the international grid detailed in IEC Publication 97. a 2000 Semtech Corp. 5 www.semtech.com SM712 PROTECTION PRODUCTS Ordering Information Par t Numbe r SM712.TC SM712.TG Qty p e r R e e l 3,000 10,000 R e e l Size 7 Inch 13 Inch Contact Information Semtech Corporation Protection Products Division 652 Mitchell Rd., Newbury Park, CA 91320 Phone: (805)498-2111 FAX (805)498-3804 a 2000 Semtech Corp. 6 www.semtech.com |
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