Circuit Note CN-0373 Devices Connected/Referenced 2.5 kV, Signal and Power Isolated, Dual ADM3252E Channel, RS-232 Line Driver/Receiver Circuits from the Lab® reference designs are engineered and tested for quick and easy system integration to help solve today’s analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0373. ADM2587E 2.5 kV, Signal and Power Isolated, ±15 kV ESD Protected, Full/Half-Duplex, RS-485 Transceiver ADuM3160 Full/Low Speed, 2.5 kV, USB Digital Isolator ADuM3070 2.5 kV, Isolated Switch Regulator With Integrated Feedback ADP190 Logic Controlled, High-Side Power Switch ADP7102 20 V, 300 mA, Low Noise, CMOS LDO Isolated USB to Isolated RS-485/Isolated RS-232 Interface EVALUATION AND DESIGN SUPPORT Circuit Evaluation Boards CN-0373 Circuit Evaluation Board (EVAL-CN0373-EB1Z) Design and Integration Files Schematics, Layout Files, Bill of Materials CIRCUIT FUNCTION AND BENEFITS The circuit shown in Figure 1 provides a completely isolated connection between the popular USB bus and an RS-485 or RS-232 bus. Both signal and power isolation ensures a safe USB device interface to an industrial bus or debug port, allowing TIA/EIA-485/232 bus traffic monitoring and the convenience of sending and receiving commands to and from a PC that is not equipped with an RS-485 or RS-232 port. Isolation in this circuit increases system safety and robustness by providing protection against electrical line surges and breaks the ground connection between bus and digital pins, thereby removing possible ground loops within the system. The TIA/EIA RS-485 bus standard is one of the most widely used physical layer bus designs in industrial and instrumentation applications. RS-485 offers differential data transmission between multiple systems, often over very long distances. RS-485 communication offers additional robustness through differential communication when compared to the RS-232 standard. TIA/EIA RS-232 devices are widely used in industrial machines, networking equipment, and scientific instruments. In modern personal computers, which are often used for debugging network problems, USB has displaced RS-232 from most of its peripheral interface roles, and many computers do not come equipped with RS-232 ports. The circuit in Figure 1 offers a robust and compact solution for both RS-232 and RS-485 interfaces. 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 Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due toanycausewhatsoeverconnectedtotheuseofanyCircuitsfromtheLabcircuits. (Continuedonlastpage) 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 ©2015 Analog Devices, Inc. All rights reserved. CN-0373 Circuit Note T2 64µH D5 VISO +3.3V L3 47µH VISO = +3.3V VIN VOUT C2 47µF C15 47µF D8 ADP190 C12 0.1µF R19 16.5kΩ J1 GND2 VIN = 6V VOUT = 5V VOUT X1 ADP7102 ADuM3070 C11 1µF SENSE R18 549Ω EN/ UVLO 10nF VDDA GND GND1 0.1µF GND1 GND1 GND1 R16 10kΩ R20 100kΩ OC 100nF GND2 VFB FB D6 LED PG C16 0.1µF VDD2 X2 NC EP VREG GND2 12MHz OSC FERRITE 600Ω FT2232H VISO = +3.3V DD– R7 UD+ DD+ VCCIO(20) VCCIO(31) VCCIO(42) SPD VCCIO(56) VREGIN VDD2 UD– VOUT BCBUS0 ADP190 ADBUS3 USB MINI D– 0.1µF VISO ADM3252E V+ C1+ ADBUS2 GND2 C1– GND2 J3/J5 RS-232 BUS RIN1 C2– GND GND2 GND1 10µF RIN2 GND2 C2+ GND2 0.1µF GND232 + C1 0.1µF 16V TOUT2 0.1µF 0.1µF C3 + 0.1µF 10V TOUT1 0.1µF GND1 FERRITE 600Ω VCC 10µF ROUT1 ROUT2 TIN1 TIN2 0.1µF GND GND485 GND2 ADBUS0 VBUS D+ GND485 VIN ADBUS1 DP J4 USB CABLE TO PC GND2 10µF 0.1µF BDBUS1 PWREN# BDBUS0 DM VBUS2 R5 OSCO OSCI VPHY 0.1µF GND2 PIN GND2 VISO = +3.3V GND2 VPLL SPU GND1 0.1µF 4.7µF GND1 Z Y GND485 GND2 VISO = +3.3V 0.1µF PDEN B 18pF GND2 4.7µF ADuM3160 A J2 RS-485 BUS VISOOUT 18pF FERRITE 600Ω VDD1 RXD RE TXD VISO = +3.3V 0.1µF VISOIN DE GND2 VBUS1 ADM2587E VCC V– GNDISO GND232 + C2 0.1µF 16V GND232 C4 + 0.1µF 16V GND2 GND1 ISOLATION BARRIER ISOLATION BARRIER Figure 1. Isolated USB to FTDI Isolated RS-232/Isolated RS-485 Circuit (Simplified Schematic, All Connections Not Shown) CIRCUIT DESCRIPTION The circuit in Figure 1 provides highly integrated and robust isolation of fully TIA/EIA-485/232 compliant transceivers. The ADM3252E 2.5 kV rms isolated RS-232 and the ADM2587E 2.5 kV rms isolated RS-485 solutions are the smallest available in the industry. The ADuM3160 provides market-leading USB port 2.5 kV rms isolation, and is easily integrated with low and full speed USB-compatible peripheral devices. The FTDI FT2232H (USB to UART converter) facilitates transmission via UART to RS-485 or RS-232 bus ports. TIA/EIA RS-232 devices are widely used in industrial machines, networking equipment, and scientific instruments. Applications for RS-485 include process control networks; industrial automation; remote terminals; building automation, such as heating, ventilation, air conditioning (HVAC) and security systems; motor control; and motion control. In these real-world systems, lightning strikes and power source fluctuations can cause damage to communications ports by generating large transient voltages. Isolation in the Figure 1 circuit increases system safety by providing protection against these electrical line surges. Rev. 0 | Page 2 of 6 12925-001 VIN Circuit Note CN-0373 12925-002 EVAL-CN0373-EB1Z Figure 2. EVAL-CN0373-EB1Z Board Figure 2 shows a photo of the isolated USB to FTDI isolated RS-232/isolated RS-485 circuit. It is possible to transmit from the USB port to both RS-485 and RS-232 ports simultaneously, if required, or to just one port. The ADuM3160 provides 2.5 kV rms digital isolation of the data signals on the D+ and D− USB bus input to the FTDI FT2232H (USB to UART converter). The isolated USB output DD− and DD+ signals are connected to the DM and DP pins of the FTDI, respectively. The FTDI FT2232H can transmit data via UART to RS-232/RS-485 depending on which PC virtual COM port (VCP) is chosen. The ADuM3160 VBUS1 power is supplied via the USB cable connection. The ADuM3070 provides a regulated isolated power source. Power (+6 V) and ground for the ADuM3070 are connected via the J1 barrel socket connector. The ADuM3160 VBUS2 pin is supplied with 3.3 V isolated power by the ADuM3070. The ADuM3070 3.3 V output also supplies the primary power for the ADM3252E 2.5 kV rms isolated RS-232 and the ADM2587E 2.5 kV rms isolated RS-485 transceiver. The ADM2587E 2.5 kV rms isolated RS-485 transceiver is the industry-leading signal and power isolated solution. This transceiver is capable of operating at 3.3 V or 5 V. Data transmits on the TxD pin, and it is received on the RxD pin. Both the driver and receiver outputs can be enabled or disabled, that is, put into a high impedance state, by changing the logic levels on the DE and RE pins, respectively. The FTDI output pin BDBUS0 is connected to the TxD data input pin of the ADM2587E. The FTDI output pins BCBUS0, PWREN#, and BDBUS1 are connected to the DE, RE, and RxD input pins of the ADM2587E, respectively. The DE and RE pin state can also be configured via the LK1 and LK2 jumpers. For each link, Position A connects the logic pin to 3.3 V, Position B connects the logic pin to GND, and Position C connects the logic pin to the FTDI output pins. The ADM2587E can transmit and receive bus data via the A, B, Y, and Z RS-485 inputs/outputs. An RS-485 bus cable can be connected via the J2 five-way connector. Disconnecting the LK5 and LK6 jumpers places the ADM2587E in a full duplex configuration, where data can be transmitted via the Y and Z pins, and received via the A and B pins. Connecting the LK5 and LK6 jumpers places the ADM2587E inputs/outputs in a half duplex configuration, which is where bus data can only be transmitted or received, but not simultaneously. The ADM3252E is a high speed, 2.5 kV, fully isolated, dual channel RS-232/V.28 transceiver device that is operational from a single 3.3 V or 5 V power supply. The RS-232 interface supports fullduplex communication and provides CTS and RTS for hardware handshaking via the J5 five-way connector or the J3 connector. J3 provides an RS-232 cable connector for connecting to industrial equipment. The ADM3252E transmitter inputs (TINx) accept TTL/CMOS input levels from the ADBUS0 and ADBUS2 output pins of the FTDI. The TINx inputs are inverted and coupled across the isolation barrier, where they are transmitted as EIA/TIA-232E bus signals via the J3 or J5 connector. The ADM3252E receiver inputs (RINx) accept EIA/TIA-232E signal levels from the J3 or J5 connector. The RINx inputs are inverted and coupled across the isolation barrier to appear at the ROUTx pins. The ROUTx pins are connected to the ADBUS1 and ADBUS3 inputs to the FTDI. Two separate ADP190 circuits are used as soft start circuitry to power the ADM2587E and ADM3252E after the FTDI FT2232H has fully powered up. Jumper LK7 links the FTDI FT2232H PWREN# pin to the EN pin of the ADP190 circuits via the 74AHC1G14W5-7 inverter. The ADP190 EN pin must be high to turn on the power switch; drive EN low to turn off the power switch. Connecting LK7 in Position A (Position B disconnected) means that the ADP190 EN pin is always high/ enabled. Connecting LK7 in Position B (Position A disconnected) means that the ADP190 EN pin is triggered via the inverted PWREN# signal. The FTDI FT2232H data sheet provides a comprehensive listing of the pin functions for RS-232 communications. The LK3 and LK4 jumpers allow handshaking options for RS-232. When LK3 is connected, ADBUS4 (DTR#) is connected to ADBUS5 (DSR#). When LK4 is connected, ADBUS4 (DTR#) is connected to ADBUS6 (DCD#). Rev. 0 | Page 3 of 6 CN-0373 Circuit Note CIRCUIT EVALUATION AND TEST Apply 6 V to the J1 barrel socket connector to power the EVALCN0373-EB1Z board. The voltage can be checked on the VCC_REG test point at the output of the ADP7102 regulator. The ADP7102 output voltage should measure 5 V. The 5 V is routed to the ADuM3070 and T2 transformer, which supply the 3.3 V outputs to power the RS-485, RS-232, and FTDI circuits. Check that the ISO_VCC test point measures 3.3 V. 12925-004 A complete transmit and receive path can be tested by connecting the RS-232 and RS-485 outputs to an Analog Devices ezLINX™ iCoupler® Isolated Interface Development Environment board. Alternatively, a USB to RS-232/RS-485 transmit test can be performed by using the Tera Term open source terminal emulator program. It is possible to transmit from the USB port to both RS-485/RS-232 ports simultaneously, if required, or to just one port. Connect a USB cable from the laptop/PC to the J4 connector. Attach an oscilloscope probe to the ISOTxD test point next to the ADM3252E transceiver, as shown in Figure 3. Open the PC application software and select COM5, then click OK, as shown in Figure 4. Figure 4. Tera Term COM5 for USB Transmission to the RS-232 Port on the EVAL-CN0373-EB1Z Board 12925-005 Load the RS-232 data to be transmitted by clicking Send under the File menu. Choose any large data size file for continuous test transmission and click Send, as shown in Figure 5. OSCILLOSCOPE J1 Observe the isolated RS-232 signal on an oscilloscope by probing the ISOTxD test point on the EVAL-CN0373-EB1Z board (see Figure 6). ADM2587E Y PC/LAPTOP Z FT2232H TERA TERM COM5 RS-232 TERA TERM COM6 RS-485 J2 RS-485 ISOTxD ADM3252E J4 USB J5 RS-232 J3 RS-232 12925-003 6.0V POWER SUPPLY Figure 5. Tera Term COM5 Data for USB Transmission to the RS-232 Port on the EVAL-CN0373-EB1Z Board 12925-006 Figure 3. Test Setup for the EVAL-CN0373-EB1Z Board Figure 6. ISOTxD Signal for the RS-232 Port on the EVAL-CN0373-EB1Z Board Rev. 0 | Page 4 of 6 Circuit Note CN-0373 12925-008 A similar test can be performed for the ADM2587E transceiver. Connect a USB cable from the laptop/PC to the J4 connector. Attach an oscilloscope probe to the Y and Z test points next to the ADM2587E transceiver as shown in Figure 3. Open a second Tera Term emulator window, and select COM6 for RS-485 transmission, as shown in Figure 7. Figure 8. Tera Term COM6 Data for USB Transmission to the RS-485 Port on the EVAL-CN0373-EB1Z Board 12925-007 Observe the isolated RS-485 signals on an oscilloscope by probing the Y and Z test points, or the differential bus signal by using the oscilloscope Y − Z Math function, as shown in Figure 9. Figure 7. Tera Term COM6 for USB Transmission to the RS-485 Port on the EVAL-CN0373-EB1Z Board 12925-009 Load the RS-485 data to be transmitted by clicking Send under the File menu. Choose any large data size file for continuous test transmission and click Send, as shown in Figure 8. Figure 9. Math Y – Z Waveform for the RS-485 Port on the EVAL-CN0373-EB1Z Board Rev. 0 | Page 5 of 6 CN-0373 Circuit Note LEARN MORE Data Sheets and Evaluation Boards CN-0373 Design Support Package: www.analog.com/CN0373-DesignSupport ADM2587E Data Sheet ezLINX™ iCoupler® Isolated Interface Development Environment, ezLINX Board Quick Start Guide. ADuM3160 Data Sheet Marais, Hein. AN-960 Application Note. RS-485/RS-422 Circuit Implementation Guide. Analog Devices, Inc. ADP190 Data Sheet Clark, Sean and Ronn Kliger. AN-740 Application Note. iCoupler® Isolation in RS-232 Applications. Analog Devices, Inc. UG-400 User Guide. ezLINX™ iCoupler® Isolated Interface Development Environment. Analog Devices, Inc. ADM3252E Data Sheet ADuM3070 Data Sheet ADP7102 Data Sheet ezLINX™ iCoupler® Isolated Interface Development Environment (EZLINX-IIIDE-EBZ) REVISION HISTORY 4/15—Revision 0: Initial Version (Continued from first page) Circuits from the Lab reference designs 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 reference designs 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 reference designs. Information furnished by Analog Devices is believed to be accurate and reliable. However, Circuits from the Lab reference designs 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 reference designs at any time without notice but is under no obligation to do so. ©2015 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN12925-0-4/15(0) Rev. 0 | Page 6 of 6