MAXREFDES67# Design

The universal analog input is the most functional, ubiquitous element in factory automation. The ability to flexibly measure current, voltage, RTDs, and TCs makes the universal input an indispensable piece in any installation. In parallel, Industry 4.0 marks a sea change in industrial architectures, characterized by distributed, intelligent control systems. Industry 4.0 allows for highly configurable, highly modular factories, which accept an ever increasing number of sensor inputs while operating at a higher output than ever before. Building a universal input in the ultrasmall micro PLC form factor marries this indispensible element with the key concepts of Industry 4.0. Furthermore, this board requires a number of highly integrated analog and mixed signal products providing high performance with ultra-low power consumption in an ultra-small package. MAXREFDES67# is Maxim’s micro PLC, universal analog input card. The MAXREFDES67# features an analog input that supports voltage, current, RTD, and thermocouple input signals with isolated power and data. The MAXREFDES67# design integrates two beyond-the-rail SPST analog switches (MAX14759), two beyond-the-rail SPDT analog switches (MAX14763), a dual beyond-the-rail buffer (MAX44267), a quad low-noise low-power op amp (MAX44245), a digital thermometer (MAX31723), a 24-bit 6-channel ADC (MAX11254) with internal PGA buffers, an ultra-high-precision 4.096V voltage reference (MAX6126), a low-power precision op amp (MAX44244), 2.75kVRMS data isolation (MAX14930 and MAX14932), a STM32F4 microcontroller, a FTDI USB-UART bridge, a high-efficiency DC-DC converter (MAX17552), and isolated/regulated +15V and +3.6V power rails (MAX17498C and two MAX17651s). The entire system typically operates at less than 500mW and fits into a space roughly the size of a credit card. While targeted for industrial, micro PLC applications, the MAXREFDES67# may be used in any application that requires high-accuracy analog-to-digital conversion.