Circuit Note CN-0313 Devices Connected/Referenced Circuits from the Lab reference circuits are engineered and 15 kV ESD-Protected, 3.3 V,12 Mbps, tested for quick and easy system integration to help solve todays ADM3485E EIA RS-485 Transceiver analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0313. EMC Compliant RS-485 Transceiver Protection Circuits using the ADM3485E transceiver. Each solution was tested and EVALUATION AND DESIGN SUPPORT characterized to ensure that the dynamic interaction between Circuit Evaluation Boards the transceiver and the protection circuit components functions CN-0313 Circuit Evaluation Board (EVAL-CN0313-SDPZ) correctly together to protect against the electrostatic discharge Design and Integration Files (ESD), electrical fast transients (EFT), and surge immunity Schematics, Layout Files, Bill of Materials specified in IEC 61000-4-2, IEC 61000-4-4, and IEC 61000-4-5, CIRCUIT FUNCTION AND BENEFITS respectively. The circuits offer proven protection for RS-485 interfaces using the ADM3485E to the ESD, EFT, and surge The circuits shown in Figure 1 demonstrate proven and tested levels often encountered in harsh environments. electromagnetic compatibility (EMC) compliant solutions for three protection levels for popular RS-485 communication ports V V CC CC ADM3485E ADM3485E TBU TBU-CA065-200-WH RO B RO B RE 120 RE 120 A A DI DI TISP DE DE TISP4240M3BJR-S TVS TVS CDS0T23-SM712 CDS0T23-SM712 PROTECTION SCHEME 1. TVS PROTECTION SCHEME 2. TVS/TBU/TISP V CC ADM3485E TBU TBU-CA065-200-WH B RO RE 120 A GDT DI 2038-15-SM-RPLF DE TVS CDS0T23-SM712 PROTECTION SCHEME 3. TVS/TBU/GDT Figure 1. Three EMC Compliant ADM3485E Protection Circuits (Simplified Schematic, All Connections Not Shown) Rev. 0 Circuits from the Lab circuits from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and determining its One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices Tel: 781.329.4700 www.analog.com be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) Fax: 781.461.3113 2013 Analog Devices, Inc. All rights reserved. 11250-001CN-0313 Circuit Note Table 1. Protection Levels Offered by Each of the Three CIRCUIT DESCRIPTION Protection Circuits in Figure 1 The RS-485 bus standard is one of the most widely used physical Protection Scheme ESD EFT (kV) Surge (kV) layer bus designs in industrial and instrumentation applications. 1. TVS 8 kV contact, 2 1 RS-485 offers differential data transmission between multiple 15 kV air discharge systems often over very long distances. Applications for RS-485 2. TVS/TBU/TISP 8 kV contact, 2 4 include process control networks industrial automation remote 15 kV air discharge terminals building automation, such as heating, ventilation, air 3. TVS/TBU/GDT 8 kV contact, 2 6 conditioning (HVAC) and security systems motor control and 15 kV air discharge motion control. Figure 2 shows a photo of the EVAL-CN0313-SDPZ board. There In these real systems, lightning strikes, power source fluctuations, are three ADM3485E devices on the board, one for each inductive switching, and electrostatic discharge can cause protection scheme. Each protection scheme provides ESD and damage to communications ports by generating large transient EFT protection as described and increasing levels of surge voltages. Designers must ensure that equipment does not just protection. work in ideal conditions, but it must also work in real-world A complete design support package for the EVAL-CN0313- conditions. To ensure that these designs can work in electrically SDPZ board including schematics, layout files, and bill of harsh environments, EMC regulations must be met. materials can be found at www.analog.com/CN0313- Many EMC problems are not simple or obvious and must be DesignSupport. considered at the start of the product development cycle. Proper solutions and protection circuits must be part of the total design effort and not left to the last minute. The protection circuits must incorporate the input and output structure of the specific transceiver manufacturer as part of the design. The IEC 61000 specifications define the set of EMC immunity requirements. Within this set of specifications, designers must be concerned with the following three types of high voltage transients for data communication lines: IEC 61000-4-2 electrostatic discharge (ESD) IEC 61000-4-4 electrical fast transients (EFT) IEC 61000-4-5 surge immunity ESD and EFT have similar rise times, pulse widths, and energy levels. The surge transient has longer rise times and pulse widths as a result, the surge transient energy can be three to four orders of magnitude larger than the energy in an ESD or EFT transient. Due to the similarities between ESD and EFT transients, the design of the circuit protection can be similar. However, due to the high energy associated with surge transients, they must be dealt with differently. Each solution protects data ports to ESD voltages of 8 kV contact and 15 kV air discharge, and EFT voltages of 2 kV. The different solutions provide an increased level of surge protection up to 6 kV. Protection levels for the circuits are summarized in Table 1. Figure 2. EVAL-CN0313-SDPZ Board Rev. 0 Page 2 of 5 11250-002