Analog DevicesEVAL-CN0179-PMDZEntwicklungssätze und Werkzeuge

Reference Design: 4-20 mA Low Power, 14-Bit, Process Control Current Loop Transmitter

The circuit is a 4 mA-to-20 mA current loop transmitter for communication between a process control system and its actuator. Besides being cost effective, this circuit offers the industry’s low power solution. The 4 mA-to-20 mA current loop has been used extensively in programmable logic controllers (PLCs) and distributed control systems (DCS’s), with digital or analog inputs and outputs. Current loop interfaces are usually preferred because they offer the most cost-effective approach to long distance noise immune data transmission. The combination of the low power AD8657 dual op amp, AD5641DAC, and ADR02 reference allows more power budget for higher power devices, such as microcontrollers and digital isolators. The circuit output is 0 mA to 20 mA of current, and it operates on a single supply from 8 V to 18 V. The 4 mA to 20 mA range is usually mapped to represent the input control range from the DAC or micro-controller, while the output current range of 0 mA to 4 mA is often used to diagnose fault conditions.

Features:

• Low power 4-20 mA current loop

• 12-, 14-, or 16-bit digital control

• Use in programmable logic controllers

Applications:

• Current monitors

• 4 mA to 20 mA loop drivers

• Buffer/level shifting

• Multipole filters

• Remote/wireless sensors

• Low power transimpedance amplifiers

Functional Test Setup

The following equipment is needed:

• PC with a USB port and Windows® XP, Windows® Vista (32-bit), or Windows® 7 (32-bit)

• EVAL-CN0179-PMDZ circuit evaluation board

• EVAL-SDP-CB1Z SDP evaluation board

• SDP-PMD-IB1Z

• CN0179 evaluation software

• Agilent E36311A dual dc power supply or equivalent

• Agilent 3458A multimeter or equivalent

• +6 V wall wart

• A GPIB-to-USB cable adapter (only required for capturing analog data from the output and transferring it to the PC)

Compatible Boards:

• EVAL-SDP-CB1Z: Blackfin® (SDP-B) controller board

• SDP-PMD-IB1Z: Pmod to SDP Adaptor Board

• Intel boards with the Pmod connector 

Related ADI parts:

• ADR02:Ultracompact, Precision 5.0 V Voltage Reference

• AD8657: 22 μA, RRIO, CMOS, 18 V Dual Operational Amplifier 

• AD5641: 2.7 V to 5.5 V, <100 µA, 14-Bit nanoDAC®, SPI Interface in LFCSP and SC70

Reference Documentation:

• ADI Pmod Daughter Cards