Circuit Note CN-0065 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. AD5422 16-Bit VOUT/IOUT DAC ADR445 Precision 5 V Reference ADuM1401 Quad-Channel Digital Isolator 16-Bit Fully Isolated Output Module Using the AD5422 Single Chip Voltage and Current Output DAC and the ADuM1401 Digital Isolator CIRCUIT FUNCTION AND BENEFITS CIRCUIT DESCRIPTION This circuit provides a complete solution for an industrial control output module. This design is suitable for process control programmable logic controllers (PLCs) and distributed control system (DCS) modules that require standard 4 mA-to20 mA current outputs and unipolar or bipolar output voltage ranges. The AD5422 16-bit DAC is software configurable to provide all necessary outputs and has many integrated diagnostic features useful in an industrial environment. The ADuM1401 provides all the necessary signal isolation between the microcontroller and the DAC. The circuit also includes standard external protection and has been tested and verified to be fully compliant with IEC 61000 specifications. For industrial control modules, standard analog output voltage and current ranges include ±5 V, ±10 V, 0 V to 5 V, 0 V to 10 V, 4 mA to 20 mA, and 0 mA to 20 mA. The AD5422 is a precision, fully integrated 16-bit DAC offering a programmable current source and programmable voltage output designed to meet the requirements of industrial process control applications. The output current range of the circuit shown in Figure 1 is programmable from 4 mA to 20 mA or 0 mA to 20 mA and has an overrange function of 0 mA to 24 mA. Voltage output is provided from a separate pin that can be configured to provide 0 V to 5 V, 0 V to 10 V, ±5 V, and ±10 V output ranges. An overrange feature of 10% is available on all ranges. Analog outputs are short- and open-circuit protected and can drive capacitive loads of 1 μF and inductive loads of 1 H. 15V ISO ADR445 0.1µF VIN VOUT + 10µF 0.1µF ISO ISO BAS70-04LT1 +15V ISO ISO +15V ISO –15V ISO + 10µF 0.1µF +5VISO + 10µF 0.1µF NPN TRANSISTOR: MMBT8099L B ISO EXTERNAL INPUT ADuM1401 3.3V 0.1µF SYNC SCLK DIN DOUT 3.3V 0V VDD1 GND1 VIA VIB VIC VOD VE1 GND1 VDD2 GND2 VOA VOB VOC VID VE2 GND2 DIGITAL ISOLATOR + 10µF ISO 1kΩ 0.1µF 0.1µF ISO AV AVSS DVCC REFIN BOOST DVCC DD SELECT IOUT LATCH +VSENSE SCLK AD5422 SDIN VOUT SDO –VSENSE CLEAR FAULTCLEAR GND SELECT RSET CCOMP 22nF C 20V TVS: SMBJ20CA E 10Ω ISO RL TVS 20V 600Ω AT 100MHz FERRITE BEAD 4nF ISO ISO –15V ISO CURRENT OUTPUT ISO ISO VOLTAGE OUTPUT TVS 20V ISO +15VISO –15V ISO 15kΩ, 0.1% BAS70-04LT1 5ppm/°C ISO 20V TVS: SMBJ20CA 08347-001 + 10µF Figure 1. 16 -Bit Industrial Control Output Module, Integrated Diagnostics, Output Protection (Simplified Schematic) Rev. B “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. www.analog.com Tel: 781.329.4700 Fax: 781.461.3113 ©2009-2011 Analog Devices, Inc. All rights reserved. CN-0065 Circuit Note output voltage error in %FSR (full-scale range) across a nominal 0 V to 10 V output range. 0.020 0.015 OUTPUT ERROR (%FSR) The ADuM1401 is a quad-channel digital isolator based on Analog Devices, Inc., iCoupler® technology. It is used to provide isolation between the AD5422 and the system microcontroller, with an isolation rating of 2.5 kV rms. All four wires are used to connect the standard SPI interface to the AD5422: three wires transmit (LATCH, SCLK, and SDIN) and one wire receives (SDO). The AD5422 has an on-board 10 ppm/°C reference. For high performance over temperature, this design uses an external ADR445 5 V reference. This device has 0.04% maximum accuracy error and a 3 ppm/°C maximum temperature drift. This drift contributes approximately 0.02% error across the industrial temperature range. 0.010 0.005 0 –0.005 –0.010 –0.015 –0.020 08347-002 By default, the DVCC pin on the AD5422 accepts a power supply of 2.7 V to 5.5 V. Alternatively, the DVCC SELECT pin can be used to connect an internal 4.5 V power supply to the DVCC pin for use as a digital power supply for other devices in the system or as a termination for pull-up resistors. Maximum current available from the DVCC pin in this mode is 5 mA. In this design, the DVCC output is used to supply the field side of the ADuM1401 digital isolator. CODE Figure 2. INL Accuracy Plot for a 0 V to 10 V Output Range Figure 2 shows a plot of the output error of the AD5422 when used with the ADR435 external reference. The data is shown as This circuit is from a portion of the PLC demo system. The PLC demo system has been successfully tested to the IEC 61000 standards shown in Table 1 (see Colm Slattery, Derrick Hartmann, and Li Ke, “PLC Evaluation Board Simplifies Design of Industrial Process Control Systems,” Analog Dialogue (April 2009) for more discussion of external protection techniques. Table 1. Conformance to IEC Specifications 1 Test Item EN55022 EN and IEC 61000-4-2 EN and IEC 61000-4-3 EN and IEC 61000-4-4 EN and IEC 61000-4-5 EN and IEC 61000-4-6 1 Description Radiated emission Class A, 3 meter anechoic chamber Electrostatic discharge (ESD) ±8 kV VCD Electrostatic discharge (ESD) ±8 kV HCD Radiated immunity 80 MHz to 1 GHz 18 V/m, vertical antenna polarization Radiated immunity 80 MHz to 1 GHz 18 V/m, horizontal antenna polarization Electrically fast transient (EFT) ±4 kV power port Electrically fast transient (EFT) ±2 kV analog I/O ports Power line surge, ±2 kV Immunity test on power cord, 10 V/m for 30 minutes Immunity test on I/O cable, 10 V/m for 30 minutes Result Passed and met −6 dB margin. Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4 are respectively −8 ppm, 10 ppm, and 13 ppm when there is interference. Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4 are respectively −8 ppm, 10 ppm, and 13 ppm when there is interference. Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4 are respectively 0.05%, 0.004%, and −0.13%. Performance automatically resorted to ≤0.05% after interference. Class B. Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4 are respectively −0.09%, 0.003%, and −0.02%. Performance automatically resorted to ≤0.05% after interference. Class B. Passed Class B. Passed Class B. No board or part damage occurred, no performance degrade, passed with Class A. Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4 are respectively 9.3%, 11%, and 3.4%. Passed Class B. Maximum deviations in Input Channel 2, Input Channel 3, and Input Channel 4 are respectively 4.5%, 4.7%, and 1.4%. Performance automatically resorted to ≤0.05% when interference stopped. A sample was tested during initial release of the PLC Demo system (V07) and met the test compliances listed in this table. These results should be viewed as typical data taken at 25°C. For these tests, the DAC outputs were connected to the ADC inputs, that is, DAC_CH2 to ADC_CH2, DAC_CH3 to ADC_CH3, and DAC_CH4 to ADC_CH4. The DAC outputs were set to 5 V, 6 V, and 10 mA, respectively. The ADC channels correspond to the circuit as in CN0067. Rev. B | Page 2 of 3 Circuit Note CN-0065 LEARN MORE Data Sheets and Evaluation Boards Cantrell, Mark. AN-0971 Application Note, Recommendations for Control of Radiated Emissions with isoPower Devices. Analog Devices. PLC Demo System. Chen, Baoxing. 2006. iCoupler® Products with isoPower™ Technology: Signal and Power Transfer Across Isolation Barrier Using Microtransformers. Analog Devices. ADuM1401 Evaluation Board. AD5422 Data Sheet. ADR445 Data Sheet. ADuM1401 Data Sheet. MT-014 Tutorial, Basic DAC Architectures I: String DACs and Thermometer (Fully Decoded) DACs, Analog Devices. REVISION HISTORY 5/11—Rev. A to Rev. B MT-015 Tutorial, Basic DAC Architectures II: Binary DACs, Analog Devices. MT-016 Tutorial, Basic DAC Architectures III: Segmented DACs, Analog Devices. Slattery, Colm, Derrick Hartmann, and Li Ke. “PLC Evaluation Board Simplifies Design of Industrial Process Control Systems.” Analog Dialogue (April 2009). Wayne, Scott. “iCoupler® Digital Isolators Protect RS-232, RS485, and CAN Buses in Industrial, Instrumentation, and Computer Applications.” Analog Dialogue (October 2005). Changes to Circuit Function and Benefits Section....................... 1 Changes to Figure 1 .......................................................................... 1 Changes to Circuit Description Section......................................... 2 Changes to Table 1 ............................................................................ 2 Changes to Learn More Section ...................................................... 3 8/09—Rev. 0 to Rev. A Updated Figure 1 ............................................................................... 1 7/09—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. ©2009-2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN08347-0-5/11(B) Rev. B | Page 3 of 3