RS-485 Port Protection
Evaluation Board 1
4/11 • FU1106
RS-485 Evaluation Board Bill of MaterialsTable 1
No. Part Number Qty. Description Reference
1TBU-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
Introduction
is 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. e recommended
Bourns® TBU® device solution, with a
low capacitance GDT, oers 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
21mm x 1.2 mm) manufactured using FR4
PCB with nickel gold plating on the top
and bottom sides.
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.
* e default conguration of this board uses 2 GDTs
(GDT1, GDT2) and discrete SMB TVS diodes
(TVS1,TVS2). e board allows dierent congurations:
•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)
RS-485 Evaluation Board Top Side Layout*
RS-485 Evaluation Board Schematic
Figure 2
Figure 1
1
TBU® HSP 1
IN1
IN2
GND
OUT1
OUT2
GND
TVS5
TVS3
TVS4
TVS1
TVS2
GDT3
GDT1
GDT2
TBU® HSP 2
1 13
2
1
3
2
1
3
3
2
1
1221
21
21
21
12 1
112 1
RS-485 Port Protection Evaluation Board 1
Performance Graphs
4/11 • FU1106
Power Cross 120 Vrms Slew Rate 1 KV/µs
Slew Rate 5 KV/µs
Figure 3 Figure 4
Figure 5
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.
1
Ch1 Ch1 -172 VMA200 ns
31.00 %
1.00 AΩCh4
200 V
Ch1 Max
508 V
Trig?PreVu
Ch4 Max
1.74 A
T
T
4
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
T
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.
1
Ch1 Ch1 312 VMA200 ns
30.40 %
1.00 AΩCh4
200 V
Ch1 Max
625 V
PreVu
Ch4 Max
1.64 A
T
T
4
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
T
Reference
For more information on implementing advanced circuit
protection technologies for RS-485 ports, please review the
Bourns® RS-485 application note:
http://www.bourns.com/data/global/pdfs/bourns_cpk1047_
rs485_circuit_protection_appnote.pdf
“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. • 4/11 • e/FU1106
For further technical support
and for complete circuit protection solutions,
please visit
www.bourns.com
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)
1
Ch1 Line -3.98 VMA2.00 ms
27.20 %
20.0 V
200 mAΩ
Ch2
Ch4
200 V
Ch1 RMS
126.7 V
Trig’dRun
Ch4 Max
371.2 mA
Ch4 Min
-359.9 mA
T
T
2
4
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
T
