Circuit Note CN-0233 Devices Connected/Referenced Quad Isolator with Integrated Circuits from the Lab reference designs are engineered and ADuM3471 Transformer Driver and PWM Controller. tested for quick and easy system integration to help solve todays analog, mixed-signal, and RF design challenges. For more 16-Bit Current Source and Voltage AD5422 information and/or support, visit www.analog.com/CN0233. 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 EVALUATION AND DESIGN SUPPORT power regulation circuitry along with associated feedback Circuit Evaluation Boards isolation. External transformers are used to transfer power CN0233 Circuit Evaluation Board (EVAL-CN0233-SDPZ) across the isolation barrier, and the entire circuit operates on a System Demonstration Platform (EVAL-SDP-CB1Z) Design and Integration Files single +5 V supply located on the primary side. This solution is Schematics, Layout Files, Bill of Materials superior to isolated power modules, which are often bulky and may provide poor output regulation. CIRCUIT FUNCTION AND BENEFITS Digital isolators are superior to opto-isolators especially when The circuit in Figure 1 provides 16-bit fully isolated 10 V and multichannel isolation is needed. The integrated design isolates 4 mA-to-20 mA outputs suitable for programmable logic the circuit from the local system controller to protect against controllers (PLCs) and distributed control systems (DCSs). ground loops and also to ensure robustness against external events often encountered in harsh industrial environments. ADR445 1:5 D1 +15V (AVDD) L1 +5V T1 V V IN OUT IN 47H + + 10F 0.1F 10F 0.1F 47F 15V (AVSS) 47F 47F D2 L2 GND ISO GND ISO GND ISO GND ISO 47H D3 AVSS R1 24.9k AVDD GND D4 R2 90.9k 10F 0.1F 10F 0.1F 0.1F + V FB + 1.25V V X1 REG R3 1 20 10.5k GND GND 1 2 2 19 GND ISO GND ISO GND ISO GND ISO 0.1F VDD VDD 1 2 +5V 3 18 +5V ADuM3471 GND ISO X2 FB 4 17 DV AV AV CC DD SS REFIN I/OA I/OA R L 5 16 LATCH I OUT CURRENT I/OB I/OB 6 15 SCLK OUTPUT I/OC I/OC 7 14 SDIN AD5422 +V SENSE GND ISO I/OD I/OD 8 13 SDO V V OUT DDA OC VOLTAGE R 100k 9 12 FAULT OC V SENSE OUTPUT 0.1F GND GND 1 2 10 11 R C CLR GND CLR SEL SET COMP GND ISO ISO GND ISO 15k GND GND ISO 0.1% 5ppm/C 4nF P4 T1: COILTRONICS KA4976-AL D1 TO D4: MBR0540 1:5 TURNS RATIO GND ISO GND ISO 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. determining its suitability and applicability for your use and application. Accordingly, in no event shall Tel: 781.329.4700 www.analog.com Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due Fax: 781.461.3113 20112014 Analog Devices, Inc. All rights reserved. to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) 10126-001CN-0233 Circuit Note 0.6 CIRCUIT DESCRIPTION The AD5422 is a fully integrated, fully programmable 16-bit 0.4 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 0.2 10 V, 5 V, 10 V. The voltage output headroom is typically 1 V, and the current output needs about 2.5 V headroom. 0 This means that the 20 mA current output can drive a load up to approximately 600 with a 15 V supply. 0.2 The ADuM347x devices are quad-channel digital isolators with 0.4 an integrated PWM controller and low impedance transformer driver outputs (X1 and X2). The only additional components 0.6 required for an isolated dc-to-dc converter are a transformer 0 8192 16384 24576 32768 40960 49152 57344 CODE and simple full-wave diode rectifier. The devices provide up to Figure 2. Measured DNL of Circuit for 10 V Output Range 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 dc- The average output noise was also tested and measured over to-dc converter. time, as shown in Figure 3. The total drift is approximately 75 V, corresponding to only 0.25 LSB. The iCoupler chip-scale transformer technology is used to 4.99855 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 4.99860 frequency is adjustable from 200 kHz to 1 MHz and is determined by the value of R . For R = 100 k, the OC OC 4.99865 switching frequency is 500 kHz. The ADuM3471 regulation is from the positive 15 V supply. 4.99870 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 4.99875 is compared with the ADuM3471 internal feedback voltage of 1.25 V. Regulation is achieved by varying the duty cycle of the 4.99880 PWM signals driving the external transformer. 0 500 1000 1500 2000 SAMPLES The negative supply is loosely regulated, and for light loads can Figure 3. Measured Average DAC Output Noise with DAC Output Set at 5 V be as high as 23 V. This is within the maximum operating on 10 V Output Range, Vertical Scale: 50 V/div value of 26.4 V specification for the AD5422. With nominal (1 LSB = 305 V), 2000 Samples loads greater than 1 k, the additional power dissipation due to 0.6 the larger unregulated negative supply voltage is not a problem. In applications that require higher compliance voltages or 0.5 where very low power dissipation is required, a different power supply design should be considered. 0.4 This circuit was tested with the ADR445 5 V, high precision, 4mA TO 20mA 0.3 0mA TO 20mA low drift (3 ppm/C maximum for B grade) external reference. 0mA TO 24mA This allows total system errors of less than 0.1% to be achieved 0.2 over the industrial temperature range (40C to +85C). The AD5422 has a high precision integrated internal reference 0.1 with a drift of 10 ppm/C maximum. If this reference is used rather than the external reference, only 0.065% additional error 0 0 12800 25600 38400 51200 64000 is incurred across the industrial temperature range. CODE Test Data and Results Figure 4. Measured Error (% FSR) For Current Output Ranges 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 V (V) OUT OUTPUT ERROR (% FSR) DNL (LSB) 10126-002 10126-004 10126-003