16-Bit Fully Isolated 4 mA to 20 mA Output Module Using the AD5662 DAC, ADuM1401 Digital Isolator, and External Amplifiers
Figure 1. 16-Bit Isolated 4 mA to 20 mA Industrial Control Output Module (Simplified Schematic)
The ADR02 has drift specs of 9 ppm/°C maximum. It is also often used in industrial applications due to its high input voltage range to 36 V.
The ADuM1401 is a quad-channel digital isolator based on Analog Devices iCoupler® technology. It is used to provide isolation between the AD5662 and the system microcontroller, with an isolation rating of 2.5 kV rms. Three wires are used ( (SYNC, SCLK, and DIN), which connect the standard SPI connections to the AD5662.
Figure 2. INL Accuracy Plot for 24 mA Full-Scale Output Range
Figure 2 shows an output error plot (integral nonlinearity) of the current output of the circuit into RL when the AD5662 is used with the ADR02 external reference. Results are shown in % FSR (full scale range) as a function of input code. The ADR02 was chosen as the reference for this circuit.
See Colm Slattery, Derrick Hartmann, Li Ke, “PLC Evaluation Board SimplifiesDesign of Industrial Process Control Systems,” Analog Dialogue, 43-04, April 2009, for more discussion of external protection techniques.
|AD5662||2.7-5.5V, 16-Bit nanoDAC® Converter in a Sot-23||
|ADR02||Ultracompact, Precision 5.0 V Voltage Reference||
|AD822||Single-Supply, Rail-to-Rail Low Power FET-Input Dual Op Amp|
|ADUM1401||Quad-Channel Digital Isolator (3/1 Channel Directionality)||