Circuit Note CN-0416 Devices Connected/Referenced 16 Mbps, 5 kV rms Signal and Power Circuits from the Lab reference designs are engineered ADM2682E Isolated RS-485 Transceiver with 15 kV and tested for quick and easy system integration to help solve ESD Protection todays analog, mixed-signal, and RF design challenges. 60 V Fault Protected 3 V to 5.5 V For more information and/or support, visit LTC2865 RS-485/RS-422 Transceivers www.analog.com/CN0416. ADP7102 3.3 V, 300 mA, Low Noise, CMOS LDO Robust, Configurable , Isolated and Nonisolated RS-485 Transceiver The isolated interface, however, allows up to 500 V between the EVALUATION AND DESIGN SUPPORT controller ground and RS-485 signals for large scale systems Circuit Evaluation Boards requiring robust communications between remote nodes, such CN-0416 Circuit Evaluation Board (EVAL-CN0416-ARDZ) as building-to-building communications. Eliminating common- Arduino Form Factor-Compatible Development Board mode effects in long haul networks requires nodes or repeaters (EVAL-ADICUP3029) Design and Integration Files to be isolated from one another and the isolated transceiver, Schematics, Layout Files, Bill of Materials certified in accordance with the UL1577, allows protection and insulation for up to 5000 V between the controller ground and CIRCUIT FUNCTION AND BENEFITS RS-485 signals (1 minute, per UL1577). The TIA/EIA-485-A, the most widely used transmission line The circuit is configurable to operate in full-duplex and half- standard of the telecommunication industry, describes the duplex operations, depending on the application. The physical layer of the RS-485 interface and is normally used with termination for each connection can be open or resistance a higher level protocol, such as Profibus, Interbus, Modbus, or terminated, which allows customers to easily add or remove BACnet. Applications include process control networks, industrial nodes to the bus lines. Furthermore, the termination resistance automation, remote terminals, building automation (such as is configurable to support standard RS-485 cables or CAT5 heating, ventilation, air conditioning (HVAC)), security systems, Ethernet cables. Power to the device can be sourced from an motor control, and motion control. The RS-485 interface allows onboard supply or from the bus power lines. for robust data transmission over relatively long distances (up to 1 km). The circuit can be used for point to point systems or multidrop systems using the onboard address selector. Each circuit can be The circuit shown in Figure 1 is a universal RS-485 communi- set as a master device or slave device, depending on the cation platform, implementing both isolated and nonisolated particular application and network in which it is used. The on- RS-485 designs. The nonisolated circuit provides an extended board 10-pin connector, compatible with the ADALM- common-mode range of 25 V, improving on the RS-485 speci- UARTJTAG, allows the master to act as the gateway between a fication of 7 V to +12 V and avoiding the need for isolation in host computer and the RS-485 bus via a USB virtual COM port. many applications, such as the case when all nodes are supplied and referenced to the same power and ground lines. Rev. 0 Circuits from the Lab reference designs 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 suitability and applicability for your use and application. Accordingly, in no event shall One Technology Way, P.O. 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CN-0416 Circuit Note GND ISO U1 S7 8 8 ADM2682E DPDPT 7 7 SWITCH S5 V 6 6 VISO ISOOUT 4PDT SWITCH 5 5 V ISOIN IOREF V 4 4 CC R12 R13 3 3 A B 120 100 Tx TxD 2 2 S2 R15 R14 B Z 1 1 4P4T SWITCH Rx RxD 100 120 Y Y P5 P4 DE SWITCH POSITIONS R145 R145 Z A 1: ISOLATED HALF DUPLEX PORT PORT RE 2: ISOLATED FULL DUPLEX V ISO GND GND 3: NON-ISOLATED FULL DUPLEX 1 2 SWITCH POSITIONS 4: NON-ISOLATED HALF DUPLEX 1: FULL DUPLEX GND GND ISO 2: HALF DUPLEX GND S6 DPDPT 8 8 SWITCH U3 7 7 S4 LTC2865 4PDT SWITCH 6 6 5 5 5V ARD V CC 4 4 R8 R9 3 3 A B IOREF 120 100 V L 2 2 Tx B Z R10 R11 DI 1 1 100 120 Rx DO Y Y P6 P24 R145 R145 DE A Z PORT PORT RE 3V3D GND 3V3D SLO R2 SWITCH POSITIONS 10k 1: FULL DUPLEX GND 2: HALF DUPLEX Figure 1. Isolated and Nonisolated RS-485 Transceiver Simplified Schematic Table 1 shows the some of the specifications of the RS-485 bus CIRCUIT DESCRIPTION standard, as well as the improved specifications that the RS-485 Bus Standard ADM2682E and LTC2865 provide. The RS-485 bus standard is one of the most commonly used For the full details of each transceiver device, refer to their data physical layers in industrial applications needing local networks sheets. The extended specifications of the ADM2682E and capable of multidrop communication links and long haul data LTC2865 improve the robustness of systems that are nominally transfer over distances up to 1200 m. A data rate of 10 Mpbs is compliant but may occasionally experience events that break achievable for cable lengths up to 12 m, dropping to 100 kbps at the standard. For example, two equipment cabinets in a factory 1200 m, as shown in Figure 2. may both be tied to earth ground, with a few volts ac between 10k grounds. However, an ESD strike to one cabinet may momentarily drive its common-mode voltage to 20 V. An LTC2865 rides through such an event, while a transceiver that 1k just meets the standard may produce corrupt data or fail entirely. The ADM2682E greatly extends common-mode tolerance, RS485 allowing for 25 kV/s transient immunity, with up to 5000 V SPECIFIED LIMITS 100 potential difference between devices (1 minute, per UL1577). Refer to the ADM2682E data sheet for details on safety and regulatory approvals. 10 10k 50k 100k 500k 1M 5M 10M DATA RATE (bps) Figure 2. Cable Length vs. Data Rate Rev. 0 Page 2 of 9 CABLE LENGTH (m) 17343-002 17343-001