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    Analog Demo Boards > Interface / Communications > HART modem >
    • Reference Design for Fully Isolated, Single Channel Voltage and 4 mA to 20 mA Output with HART
    • Reference Design for Fully Isolated, Single Channel Voltage and 4 mA to 20 mA Output with HART


    The EVAL-CN0321-SDPZ evaluation board circuit provides a complete, fully isolated, analog output channel suitable for programmable logic controllers (PLCs) and distributed control system (DCS) modules that require standard 4 mA to 20 mA HART®1-compatible current outputs and unipolar or bipolar output voltage ranges. It provides a flexible building block for channel-to-channel isolated PLC/DCS output modules or any other industrial application that requires a fully isolated analog output. The circuit also includes external protection on the analog output terminals.

    The AD5422 16-bit digital-to-analog converter (DAC) is software configurable and provides all the necessary current and voltage outputs. The AD5700-1, the industry’s 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.

    PLC/DCS solutions must be isolated from the local system controller to protect against ground loops and to ensure robustness against external events. Traditional solutions use discrete ICs for both power and digital isolation. When multichannel isolation is needed, the cost and space of providing discrete power solutions becomes a big disadvantage. Solutions based on optoisolators typically have reasonable output regulation but require additional external components, thereby increasing board area. Power modules are often bulky and can provide poor output regulation. The circuit in Figure 1 uses the ADuM347x family of isolators and power regulation circuitry along with associated feedback isolation. External transformers are used to transfer power across the isolation barrier.

    The ADuM3482 provides the UART signal isolation for the AD5700-1. The ADP2441, 36 V step-down dc-to-dc regulator, accepts an industrial standard 24 V supply, with wide tolerance on the input voltage. It steps this down to 5 V to power all controller side circuitry. The circuit also includes standard external protection on the 24 V supply terminals, as well as protection against dc overvoltage of +36 V down to −28 V.

    The EVAL-CN0321-SDPZ evaluation board circuit uses EVAL-SDP-CB1Z system demonstration platform (SDP-B). Install the evaluation software before connecting the evaluation board and SDP board to the USB port of the PC to ensure that the evaluation system is correctly recognized when connected to the PC.

    Key Applications: Programmable Logic Controllers/ Distributed Control Systems


    • Voltage and 4mA to 20mA output
    • Fully isolated
    • HART connectivity

    Ships With

    • Evaluation Board
    • Software CD

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