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 More detailed image (2MB) 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 420mA current loop or a 0.2V to 4.096V voltage input signal, and features isolated power and dataall 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 data isolation (MAX14850), and isolated/regulated 5V power rails (MAX256/MAX1659). RMS 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. Page 1 of 10Figure 1. The Campbell subsystem design block diagram. Features Applications High accuracy 420mA current loop input Industrial sensors 0.2V to 4.096V input range Process control Isolated power and data Industrial automation Small printed circuit board (PCB) area PLC Device drivers Medical Example C source code 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. This module is designed only for a supply voltage of 3.3V and uses the SPI pin assignments as illustrated on the right. The power requirements are shown in Table 1. The currently supported platforms and ports are shown in Table 2. Table 1. Power Options for the Campbell Subsystem Reference Design Jumper Input Input Current Power Type Shunt Voltage (V) (mA, typ) On-board isolated JU3: 12 3.3 72.5 power JU4: 23 JU3: 23 External power 12 10.7 JU4: 12 Page 2 of 10