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- Campbell (MAXREFDES4#): 16-Bit High-Accuracy 4-20mA Input Isolated Analog Front End (AFE) - Sub-System Board - Maxim

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Maxim > Design Support > Technical Documents > Sub-System Boards > APP 5562

Keywords: Campbell, MAXREFDES4, subsystem reference design, analog front end, AFE, industrial sensors,

isolated power and data, industrial automation, 4-20mA, current loop, PLC, medical

SUB-SYSTEM BOARD 5562

Campbell (MAXREFDES4#): 16-Bit High-Accuracy 4-

20mA Input Isolated Analog Front End (AFE)

Jan 16, 2013

Abstract: This document explains how the Campbell (MAXREFDES4#) subsystem reference design meets the

higher resolution and isolation needs of industrial control and industrial automation applications. Hardware and

firmware design files as well as FFTs and histograms from lab measurements are provided.

Introduction

In industrial control and industrial

automation applications, high-resolution

data converters are often required.

Although today's field programmable gate

arrays (FPGAs) and microcontrollers may

integrate analog-to-digital converters

(ADCs), in many cases, the resolution is

not high enough and isolation is lacking.

The Campbell (MAXREFDES4#) subsystem reference design is a 16-bit high-accuracy industrial analog front

end (AFE) that accepts a 4–20mA current loop or a 0.2V to 4.096V voltage input signal, and features isolated

power and data—all integrated into a small form factor. The Campbell design integrates a precision low-noise

buffer (MAX44250), a high-accuracy ADC (MAX11100), an ultra-high-precision 4.096V voltage reference

(MAX6126), 600V

RMS

data isolation (MAX14850), and isolated/regulated 5V power rails (MAX256/MAX1659).

This AFE solution can be used in any application that needs high-accuracy analog-to-digital conversion, but it is

mainly targeted for industrial sensors, industrial automation, process control, programmable logic controllers

(PLCs), and medical applications.

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Summary of content (10 pages)

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Maxim > Design Support > Technical Documents > Sub-System Boards > APP 5562 Keywords: Campbell, MAXREFDES4, subsystem reference design, analog front end, AFE, industrial sensors, isolated power and data, industrial automation, 4-20mA, current loop, PLC, medical SUB-SYSTEM BOARD 5562 Campbell (MAXREFDES4#): 16-Bit High-Accuracy 420mA Input Isolated Analog Front End (AFE) Jan 16, 2013 Abstract: This document explains how the Campbell (MAXREFDES4#) subsystem reference design meets the higher resolution and i
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Figure 1. The Campbell subsystem design block diagram. Features Applications High accuracy 4–20mA current loop input 0.2V to 4.096V input range Isolated power and data Small printed circuit board (PCB) area Device drivers Example C source code Industrial sensors Process control Industrial automation PLC Medical Pmod™-compatible form factor Detailed Description of Hardware The Pmod specification allows for both 3.3V and 5V modules as well as various pin assignments.
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Table 2. Supported Platforms and Ports Supported Platforms Port Nexys ™ 3 Platform (Spartan® -6) JB1 ZedBoard ™ platform (Zynq ® -7020) JA1 The Campbell subsystem is best suited for a high-accuracy 4–20mA current loop or a 0.2V to 4.096V input voltage analog-to-digital data acquisition system. The hardware design provides both isolated power (MAX256) and isolated data (MAX14850).
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Figure 2a. The Campbell firmware flowchart for Nexys 3 Platform. The firmware accepts commands, writes status, and is capable of downloading blocks of sampled data to a standard terminal program via a virtual COM port. The complete source code is provided to speed up customer development. Code documentation can be found in the corresponding firmware platform files.
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Figure 2b. The Campbell firmware flowchart for ZedBoard platform. The firmware accepts commands, writes statuses, and is capable of downloading blocks of sampled data to a standard terminal program via a virtual COM port. The complete source code is provided to speed up customer development. Code documentation can be found in the corresponding firmware platform files. Quick Start Required equipment: Windows® PC with two USB ports Campbell (MAXREFDES4#) board Campbell-supported platform (i.e.
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Lab Measurements Equipment used: Audio Precision ® SYS-2722 signal source or equivalent Voltage calibrator DVC-8500 Windows PC with two USB ports Campbell (MAXREFDES4#) board Nexys 3 development kit 12V DC power supply (for external power testing only) Special care must be taken and the proper equipment must be used when testing the Campbell design. The key to testing any high-accuracy design is to use sources and measurement equipment that are of higher accuracy than the design under test.
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Figure 4. DC histogram using on-board isolated power; a 2.0V input signal; high-impedance input; a 20ksps sample rate; 65,536 samples; a code spread of 6 LSBs with 96.57% of the codes falling within the three center LSBs; and a standard deviation of 0.702.
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Figure 5. AC FFT using external power, a 0.2V to 4.08V 1kHz sine wave input signal, high-impedance input, a 20ksps sample rate, and a Blackman-Harris window.
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Figure 6. DC histogram using external power; a 2.0V input signal; high-impedance input; a 20ksps sample rate; 65,536 samples; a code spread of 7 LSBs with 96.94% of the codes falling within the three center LSBs; and a standard deviation of 0.721. All Design Files Download all design files. Hardware Files Schematic Bill of materials (BOM) PCB layout PCB Gerber PCB CAD (PADS 9.
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ARM is a registered trademark and registered service mark of ARM Limited. Audio Precision is a registered trademark of Audio Precision, Inc. AutoShutdown is a trademark of Maxim Integrated Products, Inc. Cortex is a registered trademark of ARM Limited. Eclipse is a trademark of Eclipse Foundation, Inc. Halo is a registered trademark of Halo Electronics, Inc. MicroBlaze is a trademark of Xilinx, Inc. Nexys is a trademark of Digilent Inc. Pmod is a trademark of Digilent Inc.