Circuit Note CN-0031 Devices Connected/Referenced Circuit Designs Using Analog Devices Products Apply these product pairings quickly and with confidence. For more information and/or support call 1-800-AnalogD (1-800-262-5643) or visit www.analog.com/circuit. ADM2485 High Speed Isolated RS-485 Transceiver ADP3330 High Accuracy, Low Dropout Linear Regulator Half-Duplex, Isolated RS-485 Interface node. The ADM2485 integrates a transformer driver that, when used with an external transformer and LDO, generates an isolated 5 V power supply to be supplied between VDD2 and GND2. CIRCUIT FUNCTION AND BENEFITS This circuit provides a half-duplex, isolated RS-485 interface using the ADM2485 high speed, isolated RS-485 transceiver and the ADP3330 high accuracy linear regulator. This circuit achieves signal and power isolation and at the same time decreases board space and power consumption. The oscillator outputs D1 and D2 of the ADM2485 drive the center tapped transformer T1. A pair of Schottky diodes and a smoothing capacitor are used to create a rectified signal from the secondary winding. The ADP3330 linear voltage regulator provides a regulated 5 V power supply to the ADM2485 busside circuitry (VDD2) as shown in Figure 1. CIRCUIT DESCRIPTION The ADM2485 is a half-duplex RS-485 transceiver that can easily achieve a fully isolated RS-485 PROFIBUS compliant T1 RECTIFIER LDO 1N5817 IN VDD1 +5V ISO OUT 10µF ADP3330 SD GND ERR 5V/3.3V POWER SUPPLY 22µF 10µF MLC 1N5817 100nF 100nF D1 GND2 D2 VDD1 VDD2 ADM2485 OSC VDD1 A TxD ENCODE DECODE RS-485 CABLE RT D B RTS ENCODE DECODE DECODE ENCODE DE OUT UART RE GND1 DIGITAL ISOLATION iCoupler GND1 ISOLATION BARRIER R RS-485 TRANSCEIVER GND2 08256-001 RxD Figure 1. Half-Duplex Isolated RS-485 Interface Using ADM2485 and ADP3330 (Simplified Schematic) Rev. A “Circuits from the Lab” 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 Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause whatsoever connected to the use of any“Circuit from the Lab”. (Continued on last page) One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2008–2009 Analog Devices, Inc. All rights reserved. CN-0031 Circuit Note COMMON VARIATIONS LEARN MORE When the ADM2485 is powered by 3.3 V on the logic side, a 1CT:2.2CT transformer T1 is required to step up the 3.3 V to 6 V, thereby ensuring enough headroom for the ADP3330 LDO to output a regulated 5 V output. Chen, Baoxing. 2006. iCoupler® Products with isoPower® Technology: Signal and Power Transfer Across Isolation Barrier Using Microtransformers. Analog Devices. If the ADM2485 is powered by 5 V on the logic side, a 1CT:1.5CT transformer T1 is required to ensure enough headroom for the ADP3330 LDO to output a regulated 5 V output. Wayne, Scott. 2005. “iCoupler® Digital Isolators Protect RS-232, RS-485, and CAN Buses in Industrial, Instrumentation, and Computer Applications.” Analog Dialogue, Volume 39. Analog Devices (October). The external transformer used with the ADM2485 must have a center-tapped winding. The turns ratio of the transformer must be set to provide the minimum required output voltage at the maximum anticipated load current with the minimum input voltage. Table 1 shows suitable transformers for the ADM2485 circuit of Figure 1. Data Sheets Table 1. Transformer Suppliers 6/09—Rev. 0 to Rev. A Manufacturer Primary Voltage 3.3V Primary Voltage 5V Coilcraft DA2304-AL DA2303-AL C&D Technologies 782482/35C 782485/55C ADM2485 Data Sheet. ADP3330 Data Sheet. REVISION HISTORY Updated Format .................................................................. Universal 10/08—Revision 0: Initial Version (Continued from first page) "Circuits from the Lab" are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may use the "Circuits from the Lab" in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of the "Circuits from the Lab". Information furnished by Analog Devices is believed to be accurate and reliable. However, "Circuits from the Lab" are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any "Circuits from the Lab" at any time without notice, but is under no obligation to do so. Trademarks and registered trademarks are the property of their respective owners. ©2008–2009 Analog Devices, Inc. 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