Circuit Note CN-0064 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. AD5662 16-Bit VOUT/IOUT DAC ADR02 Precision 5 V Reference AD822 Dual, Precision 36 V FET Amplifier ADuM1401 Quad-Channel Digital Isolator 16-Bit Fully Isolated 4 mA to 20 mA Output Module Using the AD5662 DAC, ADuM1401 Digital Isolator, and External Amplifiers CIRCUIT FUNCTION AND BENEFITS AD822 op amp. The AD822 amplifier was chosen for its high performance, high voltage operation. The first stage of the current mirror needs to operate at 0 V input to ensure there is no dead band when the DAC operates at zero-scale output. This requires that the negative supply to the AD822 be at least −1 V so that there is sufficient headroom on the output of the first stage AD822. The two diodes in the second stage, which are in series with the positive power supply, ensure that the output voltage of the second stage does not go to the positive supply rail of the AD822, which can be as high as 35 V. The output of the FET is also protected by a series diode. Note that this series diode will increase the power dissipation of the circuit, which may be an issue in some applications. 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 and transmitters that require a 4 mA to 20 mA current output range. The AD5662 nanoDAC® is a 5 V16-bit DAC in a SOT-23 package. The ADuM1401 fourchannel digital isolator provides all the necessary signal isolation between the microcontroller and the DAC. CIRCUIT DESCRIPTION For industrial control modules, analog output current ranges are typically 4 mA to 20 mA or 0 mA to 20 mA. The AD5662 provides a 0 V to 5 V output, which sets the current through the sense resistor RS and, therefore, the current through R1.This current is mirrored (10×) to R2, using the second half of the 15VISO ADR02 VOUT 0.1µF ISO +15VISO + 10µF EXTERNAL INPUT SYNC SCLK DIN 3.3V 0V VDD1 VDD2 GND1 GND2 R1 1kΩ 10ppm/°C ISO 0.1µF VDD VIA VOA SYNC VIB VOB SCLK VIC VOC DIN VOD VID VE1 VE2 GND1 +15VISO 0.1µF 22µH 3.3V 0.1µF VREF + VFB 10µF 0.1µF AD5662 VOUT GND ISO (1) G BZX84C18LT1 100Ω (2) 2kΩ + 0.1µF ISO S G 10µF IRFU9014 D AD822 S BAS21LT1 IRFU024N D AD822 ISO + 10µF GND2 DIGITAL ISOLATOR R2 100Ω 10ppm/°C ISO ISO ADuM1401 1N4002 (2) 0.1µF ISO VSS <-1VISO 0.1µF RS 2.5kΩ, 0.1% 10ppm/°C ISO RL CURRENT OUTPUT ISO 08346-001 VIN Figure 1. 16-Bit Isolated 4 mA to 20 mA Industrial Control Output Module (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. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2009–2011 Analog Devices, Inc. All rights reserved. Circuit Note CN-0064 The ADR02 has drift specs of 9 ppm/°C maximum. It is also often used in industrial applications due to its high input voltage range to 36 V. Learn More The ADuM1401 is a quad-channel digital isolator based on Analog Devices iCoupler® technology. It is used to provide isolation between the AD5662 and the system microcontroller, with an isolation rating of 2.5 kV rms. Three wires are used (SYNC, SCLK, and DIN), which connect the standard SPI connections to the AD5662. Figure 2 shows an output error plot (integral nonlinearity) of the current output of the circuit into RL when the AD5662 is used with the ADR02 external reference. Results are shown in % FSR (full scale range) as a function of input code. The ADR02 was chosen as the reference for this circuit. See Colm Slattery, Derrick Hartmann, Li Ke, “PLC Evaluation Board Simplifies Design of Industrial Process Control Systems,” Analog Dialogue, April 2009, for more discussion of external protection techniques. Slattery, Colm, Derrick Hartmann, and Li Ke. “PLC Evaluation Board Simplifies Design of Industrial Process Control Systems.” Analog Dialogue (April 2009). MT-014 Tutorial, Basic DAC Architectures I: String DACs and Thermometer (Fully Decoded) DACs, Analog Devices. MT-015 Tutorial, Basic DAC Architectures II: Binary DACs, Analog Devices. MT-016 Tutorial, Basic DAC Architectures III: Segmented DACs, Analog Devices. Wayne, Scott. “iCoupler® Digital Isolators Protect RS-232, RS485, and CAN Buses in Industrial, Instrumentation, and Computer Applications.” Analog Dialogue (October 2005). Data Sheets and Evaluation Boards 0.005 AD5662 Data Sheet. 0 AD822 Data Sheet. ADR02 Data Sheet. –0.005 ADuM1401 Data Sheet. –0.010 ADuM1401 Evaluation Board. –0.015 PLC Demo System. –0.020 REVISION HISTORY –0.025 08346-002 OUTPUT ERROR (%FSR) Chen, Baoxing. 2006. iCoupler® Products with isoPower™ Technology: Signal and Power Transfer Across Isolation Barrier Using Microtransformers. Analog Devices. CODE Figure 2. INL Accuracy Plot for 24 mA Full-Scale Output Range 3/11—Rev. A to Rev. B Change to Circuit Function and Benefits.......................................1 Changes to Circuit Description .......................................................2 1/10—Rev. 0 to Rev. A Change to 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. CN08346-0-3/11(B) Rev. B | Page 2 of 2