16-Bit Isolated Input AFE

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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), 600VRMS 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.

  

Detailed Description of Firmware for ZedBoard Platform

The Campbell firmware design is also developed and tested for the ZedBoard kit and targets an ARM^® Cortex^® -A9 processor placed inside a Xilinx Zynq system-on-chip (SoC). 

An AXI MAX11100 custom IP core is created for this reference design to optimize the sampling rate and SPI timing stability. 

The firmware is a working example of how to interface to the hardware, collect samples, and save them to memory. The simple process flow is shown in Figure 2. The firmware is written in C using the Xilinx SDK tool, which is based on the Eclipse open source standard. Custom Campbell-specific design functions were created utilizing the AXI MAX11100 custom IP core. The SPI clock frequency is set to 4.54MHz when a 189.4ksps sampling rate is selected. The SPI clock frequency is set to 2.5MHz for all other sampling rate. 

 

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., Nexys 3 development kit or ZedBoard kit)
• 4–20mA current loop sensor or other signal source

To learn more about Campbell (MAXREFDES4#), click on the link below:

http://www.eeweb.com/company-blog/maxim/16-bit-isolated-input-afe/


 

*Note*

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Windows is a registered trademark and registered service mark of Microsoft Corporation.
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ZedBoard is a trademark of Avnet, Inc.
Zynq is a registered trademark of Xilinx, Inc.