Circuit Note CN-0321 Devices Connected/Referenced AD5422 16-Bit Current and Voltage Output DAC Low Power HART Modem with Internal AD5700-1 RC Oscillator Circuits from the Lab reference circuits are engineered and 36 V, 1 A, Synchronous, Step-Down tested for quick and easy system integration to help solve todays ADP2441 DC-to-DC Regulator analog, mixed-signal, and RF design challenges. For more information and/or support, visit www.analog.com/CN0321. Quad Isolator with Integrated ADuM3471 Transformer Driver and PWM Controller Small, 3.75 kV rms Quad Digital ADuM3482 Isolator Fully Isolated, Single Channel Voltage and 4 mA to 20 mA Output with HART Connectivity EVALUATION AND DESIGN SUPPORT PLC/DCS solutions must be isolated from the local system controller to protect against ground loops and to ensure robustness Circuit Evaluation Boards against external events. Traditional solutions use discrete ICs for CN0321 Evaluation Board (EVAL-CN0321-SDPZ) both power and digital isolation. When multichannel isolation is System Demonstration Platform (EVAL-SDP-CB1Z) needed, the cost and space of providing discrete power solutions Design and Integration Files becomes a big disadvantage. Solutions based on optoisolators Schematics, Layout Files, Bill of Materials typically have reasonable output regulation but require additional CIRCUIT FUNCTION AND BENEFITS external components, thereby increasing board area. Power modules are often bulky and can provide poor output regulation. This circuit provides a complete, fully isolated, analog output The circuit in Figure 1 uses the ADuM347x family of isolators and channel suitable for programmable logic controllers (PLCs) and power regulation circuitry along with associated feedback isolation. distributed control system (DCS) modules that require standard 1 External transformers are used to transfer power across the -compatible current outputs and unipolar 4 mA to 20 mA HART isolation barrier. or bipolar output voltage ranges. It provides a flexible building block for channel-to-channel isolated PLC/DCS output modules The ADuM3482 provides the UART signal isolation for the or any other industrial application that requires a fully isolated AD5700-1. analog output. The circuit also includes external protection on The ADP2441, 36 V step-down dc-to-dc regulator, accepts an the analog output terminals. industrial standard 24 V supply, with wide tolerance on the The AD5422 16-bit digital-to-analog converter (DAC) is software input voltage. It steps this down to 5 V to power all controller configurable and provides all the necessary current and voltage side circuitry. The circuit also includes standard external outputs. protection on the 24 V supply terminals, as well as protection against dc overvoltage of +36 V down to 28 V. The AD5700-1, the industrys lowest power and smallest footprint HART-compliant IC modem, is used in conjunction with the AD5422 to form a complete HART-compatible 4 mA to 20 mA solution. The AD5700-1 includes a precision internal oscillator that provides additional space savings, especially in channel-to-channel isolated applications. 1 HART is a registered trademark of the HART Communication Foundation. Rev. 0 Circuits from the Lab circuits 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. suitability and applicability for your use and application. 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CN-0321 Circuit Note 0.1F 10nF 18V TO 30V AGND VCC BST 18H 5V SW VIN 4.7F 73. 3k ADP2441 32F COMP PGND FB PGOOD FREQ SS/TRK 10k 118k R 10nF FREQ 180pF D1 L1 T1 47H C REGULATED OUT1 57F +15V C OUT2 UNREGULATED D2 57F L2 15V ADR02 47H D3 V V IN OUT R1 93. 1k 0.1F V D4 BAS70-04LT1 FB R2 10F + 0.1F 10F + 0.1F AV AV DD SS 8. 06k CURRENT 18 C3 OUTPUT 2.2F X1 V REG 10F + 0.1F TVS 0.1F 500 GND GND D5 ADuM3471 1 2 26V BAS70-04LT1 AV AV CAP1 DV REFIN V V DD1 DD2 SS DD CC AV AV DD SS SELECT DV I X2 FB CC OUT 22 LATCH +V V V SENSE IA OA AD5422 VOLTAGE LATCH SCLK 100 OUTPUT V V V IB OB OUT SCLK SDIN V V V SENSE TVS IC OC D6 2k SDO SDIN 26V 22 C V V CLEAR GND CAP2 COMP OD ID FAULT SDO VDD V 100k A OC 4nF 26V TVS: 10F 0.1F GND GND 1 2 500 SMBJ26CA AV AV DD SS 10F BAS70-04LT1 DV CC AV DD V V DDL1 DDL2 0.1F ADuM3482 10F C2 C1 5V V GND (24 ld SSOP) GND CC 22nF 1 2 2.2nF V V HART OUT IA OA TXD TXD V V IB OB RTS RTS V V OC IC CD CD V REF V OD ID RXD RXD 1F CTRL CTRL 1 2 1. 2M AD5700-1 V V DD1 DD2 300pF 150k V ADC IP V DDC2 DDC1 GND 150pF 0.1F 0.1F GND 1 2 AGND DGND 1. 2M 0.1F 0.1F Figure 1. Functional Block Diagram (Simplified Schematic: All Connections and Decoupling Not Shown) The AD5422 has an on-board 10 ppm/C reference. For higher CIRCUIT DESCRIPTION performance over temperature, this design uses an ADR02 Analog Output reference. The ADR02 is a 5 V precision reference that allows For industrial control modules, standard analog output voltage for an input voltage of up to 36 V. It has a 0.05% maximum and current ranges include 5 V, 10 V, 0 V to +5 V, 0 V to +10 V, accuracy error and a 3 ppm/C maximum temperature drift. +4 mA to +20 mA, and 0 mA to +20 mA. The AD5422 is a This drift contributes approximately 0.02% error across the precision, fully integrated 16-bit DAC that offers a programmable industrial temperature range. current source and programmable voltage output designed to The AD5422 allows for an internal or external precision, meet the requirements of industrial process control applications. current setting resistor for the current output circuitry. This The AD5422 provides all the output ranges previously listed, with design uses the internal current sensing resistor option the current output ranges and voltage output ranges available on however, even higher accuracy can be achieved by using a separate pins. An overrange feature of 10% is available on all the precision external 15 k resistor. voltage ranges, and a 0 mA to 20 mA overrange is available on the current output. Analog outputs are short- and open-circuit protected. Rev. 0 Page 2 of 8 UART SPI 11418-001