CN0063: 16-Bit Fully Isolated Voltage Output Module Using the AD5662 DAC, ADuM1401 Digital Isolator, and External Amplifiers

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OVERVIEW

Circuit Note PDF, 11/2010 (pdf, 112 kB)
Benefits & Features
  • Digitally Isolated 16-Bit Industrial Control Output Module
  • Bipolar Output Voltage
  • Error < 0.015% of FSR Over All Codes
Products Used
    Applications: 
  • Programmable Logic Controllers/ Distributed Control Systems
  • Field Instruments/ Smart Transmitters

CIRCUIT FUNCTION AND BENEFITS

This circuit provides a complete solution for an industrial control output module. This design is suitable for process control programmable logic controllers (PLCs) and distributed control systems (DCSes) that require bipolar output voltage ranges. The AD5662 nanoDAC® is a 5 V, 16-bit DAC in a SOT-23 package. The ADuM1401 four-channel digital isolator provides all the necessary signal isolation between the microcontroller and the DAC.

Figure 1.16-Bit Isolated Industrial Control Voltage Output Module (Simplified Schematic)

CIRCUIT DESCRIPTION

For industrial control modules, analog output voltage ranges are typically ±5 V, ±10 V, 0 V to 5 V, or 0 V to 10 V. The AD5662 provides a 0 V to 5 V output, which goes through two gain and offset stages to provide 16-bit resolution in each of the above ranges. Jumpers (shown here as switches) are used to switch between output ranges. The OP2177 was chosen for this design, primarily due to low noise and offset performance, as well as bipolar voltage capability.

The ADR02 was chosen as the reference for this circuit. The ADR02 has excellent ppm drift specs at 9 ppm/°C max. It is also often used in industrial applications due to its high input range to 36 V.

The ADuM1401 is a four-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 to connect the standard SPI interface connections to the AD5662: SYNC, SCLK, and DIN.

Figure 2. INL Accuracy Plot 0 V to +10 V Output Range

Figure 2 shows an output error plot (integral nonlinearity) of the output of the circuit when the AD5662 is used with the ADR02 external reference. Results are shown in %FSR (full-scale range) as a function of input code.

SAMPLE PRODUCTS USED IN THIS CIRCUIT

Product Description Available Product Models to Sample
AD5662 2.7-5.5V, 16-Bit nanoDAC® Converter in a Sot-23 AD5662ARJZ-1500RL7 AD5662BRJZ-2500RL7 AD5662BRJZ-1500RL7 AD5662BRMZ-1 AD5662ARMZ-1 AD5662BRJZ-1REEL7
ADR02 Ultracompact, Precision 5.0 V Voltage Reference ADR02AUJZ-REEL7 ADR02AKSZ-REEL7 ADR02ARZ
ADUM1401 Quad-Channel Digital Isolator (3/1 Channel Directionality) ADUM1401WTRWZ ADUM1401CRW ADUM1401ARWZ ADUM1401WSRWZ ADUM1401CRWZ ADUM1401BRWZ
OP2177 Precision Low Noise, Low Input Bias Current Dual Op Amp OP2177ARMZ OP2177ARZ
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