RS-485 Port Protection Evaluation Board 4
DESIGN NOTE
www.bourns.com 8/28 • e/K1901A
This evaluation board serves as an aid in evaluating circuit
protection solutions for RS-485 serial ports. It uses a Bourns®
TBU® High-Speed Protector (HSP), a Gas Discharge Tube (GDT)
Surge Arrestor and a Transient Voltage Suppressor (TVS)
that are designed to meet the required industry standards
on RS-485 port interfaces. The recommended Bourns® TBU®
HSP solution oers enhanced performance features over
competing technologies. These performance features can help
engineers improve the surge and transient protection level on
RS-485 ports, while allowing them to place the entire circuit
protection solution into a smaller PCB area as compared to
alternative solutions. The Bourns® RS-485 Evaluation Board 4
measures 35 mm x 25 mm x 0.85 mm, and is manufactured
using an FR-4 PCB with nickel-gold pad plating on the top and
bottom sides.
Bourns’ three previous versions of the RS-485 Evaluation
Boards (EVB1, 2 and 3) used the Bourns® Model TBU-CA, which
is a single-channel device. Because the RS-485 interface has
two lines, this new evaluation board provides further PCB area
reduction by utilizing the new Bourns® Model TBU-DF HSP,
which is a dual-channel device. This latest evaluation board is
the smallest RS-485 evaluation board oering a more compact
solution helping designers save valuable PCB real estate.
INTRODUCTION
HOW TO CONNECT THE EVALUATION BOARD
FOR TEST SET-UP
• Connect J1A and J1B to the exposed lines.
• Connect J2A and J2B to the RS-485 IC device.
RS-485 Evaluation Board 4 Top Side Layout
RS-485 Evaluation Board 4 Schematic Figure 2Figure 1
TBU® HSP
GND
B
A
GND
B
A
GND
GND
J1 J2
TISP1
TISP2
TVS
RS-485 Evaluation Board 4 Bill of MaterialsTable 1
No. Part Number Qty. Description Product
1 TBU-DF085-300-WH 1 850 V 300 mA Dual Channel Bidirectional TBU® HSP TBU® HSP
2 2030-42T-SM-RPLF 1 Fast Acting, 3-Electrode 420 V Gas Discharge Tube GDT
3 CDSOT23-SM712 1 SOT23 12 V Dual Bidirectional TVS Diode TVS Diode
The default conguration of this board uses a TBU® HSP, a GDT and a TVS diode.
The board allows dierent congurations:
• One Model 2030-42T-SM-RPLF could be replaced by two Model TISP4350J3BJR-S
• One Model 2030-42T-SM-RPLF could be replaced by two Model TISP4500H3BJR-S
• One Model 2030-42T-SM-RPLF could be replaced by one Model 2036-07-SM-RPLF
DESIGN NOTE
RS-485 Port Protection Evaluation Board 4
www.bourns.com 8/28 • e/K1901A
RS-485 EVALBOARD 4 CONFIGURATION
Bourns® TBU® High-Speed Protector (HSP) and Overvoltage Protector (OVP) CombinationTable 2
OVP Part Number OVP Surge Rating VDRM
(V)
VBO
(V)
(1000 V/µs)
TBU® HSP Part
Number Surge Capability
AC Power
Cross
Capability
TISP4350J3BJR-S 800 A, 8/20 µs
350 A, 5/310 µs 275 350 TBU-DF055-300-WH IEC61000-4-5, Level 4,
4 kV 1.2/50 μs, 42 Ohm
ITU K.20/21/45
Enhanced Lighting,
6 kV 10/700 μs, 40 Ohm
120 VAC
2030-42T-SM 500 A, 8/20 µs
150 A, 5/310 µs 360 850 TBU-DF085-300-WH 230 VAC
TISP4500H3BJR-S 200 A, 5/310 µs 350 500 TBU-DF055-300-WH 230 VAC
2036-07-SM 10,000 A, 8/20 µs
2,000 A, 5/310 µs 75 750 TBU-DF085-300-WH –
Protection of RS-485 ports are typically required in three
scenarios. The rst scenario is for exposed and harsh
environments, such as outdoor installations where induced
lightning surges are a threat. Customers for these types
of applications are familiar with the ITU-T K.20/21/44
recommendations (specifying the 10/700µs voltage, surge) or
with the Telcordia GR-1089-CORE or IEC 61000-4-5 standard
(specifying the CWG 8/20 µs current, 1.2/50 µs voltage surges).
The second scenario accommodates long cable runs where
multiple lines (data and AC power) are used in the same
trucking or cabling. During a fault incidence, the AC power lines
may come in contact with the signal lines. These applications
require 230VAC tests specied in ITU-T K.20/21/44, or 120
VAC tests specied in Telcordia GR-1089-CORE. There are
applications with lower voltage application/installation threats,
but where the standardized 120 VAC or 230 VAC tests are still
used to test the robustness of the protection solution.
The third scenario protects against installation errors and faults.
For example, 12 VDC or 24 VDC lines are frequently run together
with the signal lines. The cable runs may include other exposed
lines that can induce lightning surges onto RS-485 ports. In
addition, there is the risk of deliberate and malicious attacks on
RS-485 ports by unauthorized users. All of these can typically be
taken care of with a protection solution that meets the higher
protection levels oered in scenarios one and two.
This evaluation board brief will highlight options for two levels
of lightning surges that use a TISP® Thyristor Surge Protector for
the lower surge level and a GDT for the higher surge level. By
varying the chosen voltage, this brief will also demonstrate that
AC power cross up to 120 VAC or 230 VAC can be accommodated
by a Bourns® Model TBU-DF based RS-485 protection solution.
Overvoltage Protector (OVP) Selection:
• Breakover voltage (VBO) or impulse breakdown voltage (Vimp) of the overvoltage protector (OVP)
should be below the maximum Peak Impulse Voltage (Vimp) of the TBU® HSP.
• VBO or Vimp of the OVP should be above the maximum voltage of AC power cross (peak of VAC).
SURGE CAPABILITY
RS-485 Port Protection Evaluation Board Surge Test SetupFigure 3
TBU® HSP
RS-485
Surge Generator
1.2/50 µs, 4 kV
TISP1
TISP2
TVS
DESIGN NOTE
RS-485 Port Protection Evaluation Board 4
www.bourns.com 8/28 • e/K1901A
TBU® HSP & OVP Combination Products
1 Bourns®Model TBU-DF055-300-WH 2 Bourns® Model TISP4350J3BJR-S 1 Bourns® Model CDSOT23-SM712
Test Results Surge Capability: IEC61000-4-5 Level 4, 4 kV 1.2/50 µs
• Upon application of the 4 kV (95.2 A) surge (Channel 2), the transient current owing through TBU-DF055-300-WH
increases to trigger TBU-DF055-300-WH quickly (<1 µs).
• When the TBU-DF055-300-WH is in the blocking state, the line voltage (Channel 1) increases with the surge, as there is no
current ow into the protected interface.
• When the line voltage increases to the VBO of TISP4350J3BJR-S (350V), TISP4350J3BJR-S will trigger shunt the line to GND.
• Hence, the protected interface is only subject to a very low (300mA) transient current <1 µs and the interface exposed to a
low line voltage of 360 V momentarily.
CH1: TISP4350J3BJR-S Voltage CH2: Surge Generator Output Current
Test Results Surge Capability: IEC61000-4-5 Level 4, 6 kV 10/700 µs
• Upon application of the 6 kV (150 A) surge (Channel 2), the transient current owing through TBU-DF055-300-WH
increases to trigger TBU-DF055-300-WH quickly (<1 µs).
• When the TBU-DF055-300-WH is in the blocking state, the line voltage (Channel 1) increases with the surge, as there is no
current ow into the protected interface.
• When the line voltage increases to the VBO of TISP4350J3BJR-S (350 V), TISP4350J3BJR-S will trigger shunt the line to GND.
• Hence, the protected interface is only subject to a very low (300mA) transient current <1 µs and the interface exposed to a
low line voltage of 352 V momentarily.
CH1: TISP4350J3BJR-S Voltage CH2: Surge Generator Output Current
TBU® HSP & OVP Combination Products
1 Bourns® Model TBU-DF085-300-WH 1 Bourns® Model 2030-42T-SM-RPLF 1 Bourns® Model CDSOT23-SM712
Test Results Surge Capability: IEC61000-4-5 Level 4, 4 kV 1.2/50 µs
• Upon application of the 4 kV (95.2 A) surge (Channel 2), the transient current owing through TBU-DF085-300-WH
increases to trigger TBU-DF085-300-WH quickly (<1 µs).
• When the TBU-DF085-300-WH is in the blocking state, the line voltage (Channel 1) increases with the surge, as there is no
current ow into the protected interface.
• When the line voltage increases to the VBO of 2030-42T-SM (850V), 2030-42T-SM will trigger shunt the line to GND.
• Hence, the protected interface is only subject to a very low (300mA) transient current <1 µs and the interface exposed to a
low line voltage of 820 V momentarily.
CH1: 2030-42T-SM-RPLF Voltage CH2: Surge Generator Output Current
Test Results Surge Capability: IEC61000-4-5 Level 4, 6 kV 10/700 µs
• Upon application of the 6 kV (150 A) surge (Channel 2), the transient current owing through TBU-DF085-300-WH
increases to trigger TBU-DF085-300-WH quickly (<1 µs).
• When the TBU-DF085-300-WH is in the blocking state, the line voltage (Channel 1) increases with the surge, as there is no
current ow into the protected interface.
• When the line voltage increases to the VBO of 2030-42T-SM (850V), 2030-42T-SM will trigger shunt the line to GND.
• Hence, the protected interface is only subject to a very low (300mA) transient current <1 µs and the interface exposed to a
low line voltage of 560 V momentarily.
CH1: 2030-42T-SM-RPLF Voltage CH2: Surge Generator Output Current
Below are graphs of dierent surge tests performed on Bourns' RS-485 Evaluation Board 4 based on the various standards requirements.
Test Results for Bourns® TBU® High-Speed Protector (HSP) and Overvoltage Protector (OVP) Combination
Test Results for Bourns® TBU® High-Speed Protector (HSP) and Overvoltage Protector (OVP) Combination
Table 3
Table 4
DESIGN NOTE
RS-485 Port Protection Evaluation Board 4
www.bourns.com 8/28 • e/K1901A
TBU® HSP & OVP Combination Products
1 Bourns® Model TBU-DF055-300-WH 2 Bourns® Model TISP4500H3BJR-S 1 Bourns® Model CDSOT23-SM712
Test Results Surge Capability: IEC61000-4-5 Level 4, 4 kV 1.2/50 µs
• Upon application of the 4 kV (95.2 A) surge (Channel 2), the transient current owing through TBU-DF055-300-WH
increases to trigger TBU-DF055-300-WH quickly (<1 µs).
• When the TBU-DF055-300-WH is in the blocking state, the line voltage (Channel 1) increases with the surge, as there is no
current ow into the protected interface.
• When the line voltage increases to the VBO of TISP4500H3BJR-S (500 V), TISP4500H3BJR-S will trigger shunt the line to GND.
• Hence, the protected interface is only subject to a very low (300mA) transient current <1 µs and the interface exposed to a
low line voltage of 496 V momentarily.
CH1: TISP4500H3BJR-S Voltage CH2: Surge Generator Output Current
Test Results Surge Capability: IEC61000-4-5 Level 4, 6 kV 10/700 µs
• Upon application of the 6 kV (150 A) surge (Channel 2), the transient current owing through TBU-DF055-300-WH
increases to trigger TBU-DF055-300-WH quickly (<1 µs).
• When the TBU-DF055-300-WH is in the blocking state, the line voltage (Channel 1) increases with the surge, as there is no
current ow into the protected interface.
• When the line voltage increases to the VBO of TISP4500H3BJR-S (500 V), TISP4500H3BJR-S will trigger shunt the line to GND.
• Hence, the protected interface is only subject to a very low (300mA) transient current <1 µs and the interface exposed to a
low line voltage of 464 V momentarily.
CH1: TISP4500H3BJR-S Voltage CH2: Surge Generator Output Current
TBU® HSP & OVP Combination Products
1 Bourns® Model TBU-DF085-300-WH 1 Bourns® Model 2036-07-SM-RPLF 1 Bourns® Model CDSOT23-SM712
Test Results Surge Capability: IEC61000-4-5 Level 4, 4 kV 1.2/50 µs
• Upon application of the 4 kV (95.2 A) surge (Channel 2), the transient current owing through TBU-DF085-300-WH
increases to trigger TBU-DF085-300-WH quickly (<1 µs).
• When the TBU-DF085-300-WH is in the blocking state, the line voltage (Channel 1) increases with the surge, as there is no
current ow into the protected interface.
• When the line voltage increases to the VBO of 2036-07-SM (750 V), 2036-07-SM will trigger shunt the line to GND.
• Hence, the protected interface is only subject to a very low (300mA) transient current <1 µs and the interface exposed to a
low line voltage of 648 V momentarily.
CH1: 2036-07-SM-RPLF Voltage CH2: Surge Generator Output Current
Test Results Surge Capability: IEC61000-4-5 Level 4, 6 kV 10/700 µs
• Upon application of the 6 kV (150 A) surge (Channel 2), the transient current owing through TBU-DF085-300-WH
increases to trigger TBU-DF085-300-WH quickly (<1 µs).
• When the TBU-DF085-300-WH is in the blocking state, the line voltage (Channel 1) increases with the surge, as there is no
current ow into the protected interface.
• When the line voltage increases to the VBO of 2036-07-SM (750 V), 2036-07-SM will trigger shunt the line to GND.
• Hence, the protected interface is only subject to a very low (300mA) transient current <1 µs and the interface exposed to a
low line voltage of 592 V momentarily.
CH1: 2036-07-SM-RPLF Voltage CH2: Surge Generator Output Current
Test Results for Bourns® TBU® High-Speed Protector (HSP) and Overvoltage Protector (OVP) Combination
Test Results for Bourns® TBU® High-Speed Protector (HSP) and Overvoltage Protector (OVP) Combination
Table 5
Table 6
DESIGN NOTE
RS-485 Port Protection Evaluation Board 4
10/17 • e/T1714
www.bourns.com
COPYRIGHT© 2018 • BOURNS, INC. • 8/28 • e/K1901A
“TBU” is a registered trademark of Bourns, Inc. in the U.S. and other countries, except Japan. All references to TBU® in this document for use in Japan shall be deemed to be replaced with Bourns® TBU™.
“Bourns” and "TISP" are registered trademarks of Bourns, Inc. in the U.S. and other countries.
Asia-Pacic: Tel +886-2 256 241 17
Email asiacus@bourns.com
Americas: Tel +1-951 781-5500
Email americus@bourns.com
EMEA: Tel +36 88 520 390
Email eurocus@bourns.com
AC POWER CROSS CAPABILITY
RS-485 Port Protection Evaluation Board AC Power Cross Test SetupFigure 3
TBU® HSP
AC Power
Supply
TISP1
TISP2
TVSRS-485
TBU® HSP & OVP Combination Products
1 Bourns® Model TBU-DF055-300-WH 2 Bourns® Model TISP4350J3BJR-S 1 Bourns® Model CDSOT23-SM712
Test Results Surge Capability: AC Power Cross 120 VAC
• Bourns® Model TISP4350J3BJR-S will not be triggered since the peak voltage of 120 VAC is less than the VBO of Bourns®
Model TISP4350J3BJR-S. As a result, Bourns® Model TISP4350J3BJR-S (350 V) will maintain high impedance.
• When the AC power is applied and the line voltage (Channel 1) and line current (Channel 2) increases, Bourns® Model
TBU-DF055-300-WH triggers quickly into the blocking state when the line current reaches its ITRIGGER (300 mA), preventing
current ow into the protected port. This can be seen as the line current (Channel 2) drops to 0 mA after the Bourns® Model
TBU-DF055-300-WH triggers.
• Once the AC voltage ramps down below Vreset, Bourns® Model TBU-DF055-300-WH will reset to the conductive state and
allow current ow again.
CH1: A TBU Voltage CH2: CH2: Line A TBU Current
Test Results for Bourns® TBU® High-Speed Protector (HSP) and Overvoltage Protector (OVP) CombinationTable 7
