EVAL-CN0233-SDPZ

Circuit Note CN-0233 Devices Connected/Referenced 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/CN0233. ADuM3471 Quad Isolator with Integrated Transformer Driver and PWM Controller. AD5422 16-Bit Current Source and Voltage Output DAC ADR445 Precision 5.0 V Reference 16-Bit Isolated Industrial Voltage and Current Output DAC with Isolated DC-to-DC Supplies The circuit uses digital isolation, as well as PWM-controlled power regulation circuitry along with associated feedback isolation. External transformers are used to transfer power across the isolation barrier, and the entire circuit operates on a single +5 V supply located on the primary side. This solution is superior to isolated power modules, which are often bulky and may provide poor output regulation. EVALUATION AND DESIGN SUPPORT Circuit Evaluation Boards CN0233 Circuit Evaluation Board (EVAL-CN0233-SDPZ) System Demonstration Platform (EVAL-SDP-CB1Z) Design and Integration Files Schematics, Layout Files, Bill of Materials CIRCUIT FUNCTION AND BENEFITS Digital isolators are superior to opto-isolators especially when multichannel isolation is needed. The integrated design isolates the circuit from the local system controller to protect against ground loops and also to ensure robustness against external events often encountered in harsh industrial environments. The circuit in Figure 1 provides 16-bit fully isolated ±10 V and 4 mA-to-20 mA outputs suitable for programmable logic controllers (PLCs) and distributed control systems (DCSs). 47µF D1 D2 GND_ISO VDD1 3 X2 4 19 ADuM3471 I/OA 5 I/OB 6 I/OC 7 I/OD 8 VDDA 0.1µF GND1 18 17 16 15 14 13 9 12 10 11 GND T1: COILTRONICS KA4976-AL 1:5 TURNS RATIO +10µF 0.1µF –15V (AVSS) GND_ISO GND_ISO GND_ISO AVDD AVSS R1 24.9kΩ 20 2 VOUT 47µH D4 X1 1 GND1 VIN 10µF + 0.1µF 47µF 47µF L2 D3 GND ADR445 +15V (AVDD) L1 47µH VREG GND2 VDD2 FB VFB 1.25V R2 90.9kΩ 10µF + 0.1µF R3 10.5kΩ GND_ISO 0.1µF +5V GND_ISO +5V GND_ISO DVCC I/OA LATCH I/OB SCLK I/OC 10µF GND_ISO AVDD AVSS GND_ISO REFIN AD5422 ROC 100kΩ GND_ISO VOUT FAULT CLR CURRENT OUTPUT +VSENSE SDO OC GND2 0.1µF IOUT SDIN I/OD 0.1µF + –VSENSE RL GND_ISO VOLTAGE OUTPUT GND CLR SEL RSET CCOMP 15kΩ 0.1% 5ppm/°C GND_ISO D1 TO D4: MBR0540 GND_ISO ISO 4nF GND_ISO P4 GND_ISO 10126-001 1:5 T1 +5V IN Figure 1. Isolated 16-Bit Current and Voltage Output DAC with Isolated Power Supplies Rev. A 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 ©2011–2014 Analog Devices, Inc. All rights reserved. CN-0233 Circuit Note 0.6 CIRCUIT DESCRIPTION The AD5422 is a fully integrated, fully programmable 16-bit voltage and current output DAC, capable of programming ranges from 4 mA to 20 mA, 0 mA to 24 mA, 0 V to 5 V, 0 V to 10 V, ±5 V, ±10 V. The voltage output headroom is typically 1 V, and the current output needs about 2.5 V headroom. This means that the 20 mA current output can drive a load up to approximately 600 Ω with a 15 V supply. DNL (LSB) 0 8192 16384 24576 32768 40960 CODE 10126-002 –0.6 49152 57344 Figure 2. Measured DNL of Circuit for ±10 V Output Range The average output noise was also tested and measured over time, as shown in Figure 3. The total drift is approximately 75 µV, corresponding to only 0.25 LSB. –4.99855 –4.99860 –4.99865 –4.99870 –4.99875 –4.99880 0 500 1000 1500 2000 SAMPLES 10126-003 The negative supply is loosely regulated, and for light loads can be as high as −23 V. This is within the maximum operating value of −26.4 V specification for the AD5422. With nominal loads greater than 1 kΩ, the additional power dissipation due to the larger unregulated negative supply voltage is not a problem. In applications that require higher compliance voltages or where very low power dissipation is required, a different power supply design should be considered. –0.4 Figure 3. Measured Average DAC Output Noise with DAC Output Set at −5 V on ±10 V Output Range, Vertical Scale: 50 µV/div (1 LSB = 305 µV), 2000 Samples This circuit was tested with the ADR445 5 V, high precision, low drift (3 ppm/°C maximum for B grade) external reference. This allows total system errors of less than 0.1% to be achieved over the industrial temperature range (−40°C to +85°C). The AD5422 has a high precision integrated internal reference with a drift of 10 ppm/°C maximum. If this reference is used rather than the external reference, only 0.065% additional error is incurred across the industrial temperature range. 0.6 0.5 0.4 4mA TO 20mA 0mA TO 20mA 0mA TO 24mA 0.3 0.2 0.1 0 0 12800 25600 38400 51200 64000 CODE Test Data and Results The AD5422 differential nonlinearity (DNL) was tested to ensure no loss in system accuracy was incurred because of the switching supplies. Figure 2 shows the DNL for a ±10V range. The result shows less than 0.5 LSB DNL error. Rev. A | Page 2 of 5 Figure 4. Measured Error (% FSR) For Current Output Ranges 10126-004 The ADuM3471 regulation is from the positive 15 V supply. The feedback for regulation is from the divider network (R1, R2, R3). The resistors are chosen such that the feedback voltage is 1.25 V when the output voltage is 15 V. The feedback voltage is compared with the ADuM3471 internal feedback voltage of 1.25 V. Regulation is achieved by varying the duty cycle of the PWM signals driving the external transformer. 0 –0.2 VOUT (V) The iCoupler chip-scale transformer technology is used to isolate the logic signals, and the integrated transformer driver with isolated secondary side control provides high efficiency for the isolated dc-to-dc converter. The internal oscillator frequency is adjustable from 200 kHz to 1 MHz and is determined by the value of ROC. For ROC = 100 kΩ, the switching frequency is 500 kHz. 0.2 OUTPUT ERROR (% FSR) The ADuM347x devices are quad-channel digital isolators with an integrated PWM controller and low impedance transformer driver outputs (X1 and X2). The only additional components required for an isolated dc-to-dc converter are a transformer and simple full-wave diode rectifier. The devices provide up to 2 W of regulated, isolated power when supplied from a 5.0 V or 3.3 V input. This eliminates the need for a separate isolated dcto-dc converter. 0.4 Circuit Note CN-0233 The ADuM347x isolators (ADuM3470, ADuM3471, ADuM3472, ADuM3473, ADuM3474) provide four independent isolation channels in a variety of input/output channel configurations. These devices are also available with either a maximum data rate of 1 Mbps (A grade) or 25 Mbps (C grade). 0.5 OUTPUT ERROR (% FSR) 0.4 0.3 0.2 0.1 CIRCUIT EVALUATION AND TEST 0 This circuit was tested using the EVAL-CN0233-SDPZ circuit board and the EVAL-SDP-CB1Z connected together as shown in Figure 6. –0.1 0V TO 5V 0V TO 10V –5V TO +5V –10V TO +10V –0.2 Equipment Used to Collect Test Data –0.3 0 12800 25600 38400 51200 64000 CODE • 10126-005 –0.4 Figure 5. Measured Error (% FSR) for Voltage Output Ranges Actual error data from the circuit is shown in Figure 4 and Figure 5. The total error in the output current and voltage (% FSR) is calculated by taking the difference between the ideal output and the measured output, dividing by the FSR, and multiplying the result by 100. An error of less than 0.5% FSR error is achieved in both the current and voltage output modes as shown in Figure 4 and Figure 5, respectively. If the VOUT pin must drive large capacitive loads up to 1 μF, a 3.9 nF capacitor can be connected between the VOUT pin and the CCOMP pin of the AD5422 by connecting the P4 pins on the board using a jumper. However, the addition of this capacitor reduces the bandwidth of the output amplifier, increasing the settling time. COMMON VARIATIONS This circuit is proven to work well with good stability and accuracy with component values shown. Where the application needs only the 4 mA to 20 mA current output, a single supply scheme can be used. In this case, the positive AVCC supply can be as large as 26.4 V and, therefore, the output compliance is 26.4 V – 2.5 V = 23.9 V. With an output current of 20 mA, a load resistance as high as 1 kΩ is possible. For applications not requiring 16-bit resolution, the 12-bit AD5412 is available. • • • • • PC with a USB port and Windows® XP, Windows Vista®, (32-bit), or Windows 7 (32-bit) EVAL-CN0233-SDPZ EVAL-SDP-CB1Z Power supply: +6 V wall wart, Agilent E3630A, or equivalent Agilent 3458A, 8.5 digit multimeter or equivalent National Instruments GPIB to USB-B interface and cable (only required for capturing analog data from the DAC and transferring it to the PC). Setup and Test The circuit was tested and verified by connecting both the EVAL-CN0233-SDPZ evaluation board and the EVAL-SDPCB1Z evaluation board, as shown in Figure 6. The CN-0233 Evaluation Software is used to capture the data from the EVAL-CN0233-SDPZ circuit board using the setup seen in Figure 6. Details regarding the use of the software can be found in the CN-0233 Software User Guide. The DNL, noise data, and actual FSR error were obtained by inputting the DAC data to the EVAL-CN0233-SDPZ evaluation board using EVAL-SDP-CB1Z board connected to the PC and reading the voltage or current output results from the 3485 multimeter. The GPIB/USB interface was used to transfer the data to the PC for analysis. The CN0233 Evaluation Software was used to generate the data to the DAC. Rev. 0 | Page 3 of 5 CN-0233 Circuit Note EVAL-CN0233-SDPZ 6V SUPPLY P2 EVAL-SDP-CB1Z 120-PINS CON A OR CON B SDP IOUT VOUT GPIB MULTIMETER USB PC 10126-006 USB 10126-007 Figure 6. Functional Block Diagram of Test Setup Showing Evaluation Board Connections Figure 7. EVAL-CN0233-SDPZ PC Board Photo Rev. A | Page 4 of 5 Circuit Note CN-0233 LEARN MORE Data Sheets and Evaluation Boards CN-0233 Design Support Package: http://www.analog.com/CN0233-DesignSupport EVAL-CN0233-SDPZ CN-0065 Circuit Note, 16-Bit Fully Isolated Output Module Using the AD5422 Single Chip Voltage and Current Output DAC and the ADuM1401 Digital Isolator, Analog Devices. AD5422 Data Sheet EVAL-SDP-CB1Z AD5422 Evaluation Board (EVAL-AD5422EBZ) Cantrell, Mark. AN-0971 Application Note, Recommendations for Control of Radiated Emissions with isoPower Devices. Analog Devices. Chen, Baoxing. 2006. iCoupler® Products with isoPower™ Technology: Signal and Power Transfer Across Isolation Barrier Using Microtransformers. Analog Devices. ADuM3471 Data Sheet ADuM3471 Evaluation Board (EVAL-ADuM3471EBZ) UG-197 User Guide for ADuM3471 Evaluation Board ADR445 Data Sheet REVISION HISTORY 3/14—Rev. 0 to Rev. A 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. Slattery, Colm, Derrick Hartmann, and Li Ke. “PLC Evaluation Board Simplifies Design of Industrial Process Control Systems.” Analog Dialogue (April 2009). Changes to Circuit Function and Benefits Section and Figure 1 ..... 1 Changes to Circuit Description Section and Figure 2; Added Test Data and Results Section and Figure 4, Renumbered Sequentially; Replaced Figure 3 ...................................................... 2 Added Figure 5; Changes to Circuit Evaluation and Test Section, Equipment Used to Collect Test Data Section, and Setup and Test Section ...................................................................... 3 Changes to Figure 6; Added Figure 7 ............................................. 4 10/11—Revision 0: Initial Version Wayne, Scott. iCoupler® Digital Isolators Protect RS-232, RS-485, and CAN Buses in Industrial, Instrumentation, and Computer Applications. Analog Dialogue (October 2005). Ardizzoni, John. A Practical Guide to High-Speed Printed-CircuitBoard Layout, Analog Dialogue 39-09, September 2005. MT-031 Tutorial, Grounding Data Converters and Solving the Mystery of “AGND” and “DGND”, Analog Devices. MT-101 Tutorial, Decoupling Techniques, Analog Devices. (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. ©2011–2014 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN10126-0-3/14(0) Rev. 0 | Page 5 of 5