AN-1203 APPLICATION NOTE One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com Simplified 16-Bit, 4 mA-to-20 mA Output Solution Using the AD5420 +15V + CIRCUIT FUNCTION AND BENEFITS 0.1µF This circuit provides a 4 mA-to-20 mA output using the AD5420, a single channel, 16-bit, serial input, 4 mA-to-20 mA current source DAC. This circuit utilizes only the AD5420 product. The only external components needed are decoupling capacitors on the supply pins and reference input and a pull-up resistor for the open-drain FAULT output, which alerts to a loss of compliance voltage on the output or an over-temperature of the AD5420 device. This offers a level of integration that leads to savings in both cost and board space. This circuit is well suited for both programmable logic controllers (PLCs) and distributed control systems (DCSes) in industrial control applications. 10µF 0.1µF 10kΩ AVDD CONTROLLER DVCC DVCC SELECT AD5420 BOOST CLEAR LATCH SCLK SDIN IOUT CIRCUIT DESCRIPTION REFOUT REFIN RSET 08355-001 FAULT SDO GND IOUT 0.1µF Figure 1. Configuration of the AD5420 (Simplified Schematic) 0.020 4mA TO 20mA 0mA TO 20mA 0mA TO 24mA 0.015 Figure 2 shows that the typical accuracy of this circuit at 25°C ambient temperature is better than 0.016%. The circuit must be constructed on a multilayer PC board with a large area ground plane. Proper layout, grounding, and decoupling techniques must be used to achieve optimum performance (see Tutorial MT-031, Grounding Data Converters and Solving the Mystery of "AGND" and "DGND," and Tutorial MT-101, Decoupling Techniques). Rev. A | Page 1 of 2 0.010 0.005 0 –0.005 –0.010 TA = 25°C RLOAD = 250Ω –0.015 –0.020 0 10k 20k 30k 40k 50k DAC CODE Figure 2. Current Output Accuracy 60k 08355-002 CURRENT OUPUT ERROR (%FSR) The AD5420 is a low cost, precision, highly integrated 16-bit digital-to-analog converter offering a programmable current source output designed to meet the requirements of industrial process control applications. The current output can be programmed with the ranges of 4 mA to 20 mA, 0 mA to 20 mA, or 0 mA to 24 mA. The AD5420 contains an internal 5 V, 10 ppm/°C maximum voltage reference. This leads to further savings in both cost and board space. Operation is specified with an AVDD supply up to 24 V. However, the AD5420 is capable of operating with an AVDD supply of up to 40 V. The AD5420 contains an onchip regulated 4.5 V output (DVCC pin) capable of sourcing up to 5 mA. This can be used as a termination for pull-up resistors or to power digital circuitry, eliminating the need to generate a logic power supply. AN-1203 Application Note LEARN MORE REVISION HISTORY Kester, Walt. 2005. The Data Conversion Handbook. Analog Devices. Chapters 3 and 7. 4/13—Rev. 0 to Rev. A MT-015 Tutorial, Basic DAC Architectures II: Binary DACs. Analog Devices. Changed Document Title from CN-0098 to AN-1203 .............................................................................. Universal 7/09—Revision 0: Initial Version MT-031 Tutorial, Grounding Data Converters and Solving the Mystery of "AGND" and "DGND." Analog Devices. MT-101 Tutorial, Decoupling Techniques. Analog Devices. Voltage Reference Wizard Design Tool. Data Sheets and Evaluation Boards AD5420 Data Sheet. AD5420 Evaluation Board. ©2009–2013 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. AN08355-0-4/13(A) Rev. A | Page 2 of 2