RS-485 Port Protection Evaluation Board 1 Introduction TBU® HSP 1 1 2 1 1 1 IN1 TVS1 2 2 GDT3 3 1 2 2 2 GDT2 TVS2 1 IN2 2 1 1 OUT1 1 GND 1 OUT2 TVS5 3 2 GND 3 2 3 2 1 1 TVS3 1 1 GDT1 1 This Evaluation Board serves as an aid in evaluating circuit protection on RS-485 serial device ports, using two Bourns® TBU® High-Speed Protectors (HSP), two fast-acting GDTs and two TVS diodes to meet the required industry standards on RS-485 port interfaces. The recommended Bourns® TBU® device solution, with a low capacitance GDT, offers enhanced high-speed performance features over competing technologies, which can help the design engineer increase the surge and transient protection level on RS-485 ports and place the entire circuit protection solution into a smaller reduced PCB area. Bourns has developed an RS-485 Evaluation Board (measuring 45 mm x 21 mm x 1.2 mm) manufactured using FR4 PCB with nickel gold plating on the top and bottom sides. 1 TVS4 TBU® HSP 2 Figure 1 RS-485 Evaluation Board Schematic Figure 2 RS-485 Evaluation Board Top Side Layout* Table 1 RS-485 Evaluation Board Bill of Materials How to Connect the Evaluation Board for Test Set-up • Connect IN1 and IN2 to the exposed lines. • Connect OUT1 and OUT2 to the RS-485 IC device. * The default configuration of this board uses 2 GDTs (GDT1, GDT2) and discrete SMB TVS diodes (TVS1,TVS2). The board allows different configurations: •2 single 2031 GDTs (GDT1 and GDT2) may be replaced by a dual 2030 GDT (GDT3, not yet released) •2 SMB TVS diodes (TVS1 and TVS2) may be replaced with a) 2 SOT23 TVS diodes (TVS3, TVS4) or b) a single TVS diode array (TVS5) No. Part Number Qty. Description Reference 1 TBU-CA065-200-WH 2 TBU® Single Bidirectional Line 650 V 200 mA TBU® HSP 1, TBU® HSP 2 2 2031-23T-SM-RPLF 2 Single Line Fast-acting GDT 650 V GDT1, GDT2 3 SMBJ12CA 2 Single Bidirectional Line TVS 12 V SMB TVS1, TVS2 11/11 • FU1106 RS-485 Port Protection Evaluation Board 1 Performance Graphs Run Trig’d T PreVu Trig? T T T 1 Ch1 RMS 126.7 V 1 Ch1 Max 508 V 4 Ch4 Max 1.74 A Ch4 Max 371.2 mA 2 Ch4 Min -359.9 mA 4 Ch1 200 V Ch2 Ch4 20.0 V M 2.00 ms A Line 200 mAΩ T 27.20 % Ch 1: AC power generator Ch 2: Voltage on protected side of world (downstream of TBU® device at SMBJ12CA TVS diode side) Ch 4: Current consumed (TBU® HSP trigger current) Figure 3 -3.98 V Ch1 M 200 ns Ch4 1.00 AΩ Figure 4 A Ch1 -172 V T 31.00 % Ch 1: Surge generator Ch 2: Consumed current (TBU® HSP Trigger current) Note: The noise generated by the GDT when it fires causes a ground bounce and is reflected in current measurement at the time the GDT device is triggered. The ohm unit following the current units shown for Channel 4 (i.e. AOhm) indicates that a 50 ohm termination was used internal to the oscilloscope Power Cross 120 Vrms PreVu 200 V The ohm unit following the current units shown for Channel 4 (i.e. AOhm) indicates that a 50 ohm termination was used internal to the oscilloscope Slew Rate 1 KV/µs Reference T For more information on implementing advanced circuit protection technologies for RS-485 ports, please review the Bourns® RS-485 application note: T 1 Ch1 Max 625 V http://www.bourns.com/data/global/pdfs/Bourns_RS-485_AppNote.pdf Ch4 Max 1.64 A 4 Ch1 200 V M 200 ns Ch4 1.00 AΩ Ch 1: Surge generator Ch 2: Consumed current (TBU® HSP Trigger current) Note: The noise generated by the GDT when it fires causes a ground bounce and is reflected in current measurement at the time the GDT device is triggered. Figure 5 A Ch1 312 V T 30.40 % Slew Rate 5 KV/µs The ohm unit following the current units shown for Channel 4 (i.e. AOhm) indicates that a 50 ohm termination was used internal to the oscilloscope For further technical support and for complete circuit protection solutions, please visit www.bourns.com 11/11 • FU1106 “TBU” is a registered trademark of Bourns, Inc. in the U.S., Taiwan and European Community. “Bourns” is a registered trademark of Bourns, Inc. in the U.S. and other countries. COPYRIGHT© 2011 • BOURNS, INC. • 11/11 • e/FU1106