AN-1242: Simplified 12-Bit, 4 mA-to-20 mA Output Solution Using the AD5410 Current Source DAC
Circuit Function and Benefits
This circuit provides a 4 mA-to-20 mA output using the AD5410, a single channel, 12-bit, serial input, 4 mA-to-20 mA current source DAC. This circuit uses only the AD5410 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 overtemperature condition of the AD5410. This implementation offers a level of integration that leads to savings in both cost and board space. This circuit is well suited for both the programmable logic controllers (PLCs) and the distributed control systems (DCS) in industrial control applications.
Figure 1. Connection Circuit for the AD5410.
Circuit Description
The AD5410 is a low-cost, highly integrated 12-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 ranges of 4 mA to 20 mA, 0 mA to 20 mA, or 0 mA to 24 mA. The AD5410 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 AD5410 is capable of operating with an AVDD supply of up to 40 V. The AD5410 contains an on-chip regulated 4.5 V output (DVCC pin) capable of sourcing up to 5 mA, which can be used as a termination for pull-up resistors or to power digital circuitry, eliminating the need to generate a logic power supply voltage. Figure 2 shows that the typical accuracy of this circuit at 25°C ambient temperature is 0.011%.
Figure 2. Current Output Accuracy.
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 MT-015 Tutorial and MT-101 Tutorial).
References
Kester, Walt. 2005. The Data Conversion Handbook, Chapter 3 and Chapter 7. Analog Devices.
MT-015 Tutorial, Basic DAC Architectures II: Binary DACs. Analog Devices.
MT-031 Tutorial, Grounding Data Converters and Solving the Myster of AGND and DGND. Analog Devices.
MT-101 Tutorial, Decoupling Techniques. Analog Devices. Voltage Reference Wizard Design Tool.