The MAXREFDES1152 is a four-channel universal analog input that measures voltage or current signals. Each channel can be configured for voltage input at 0 to 10V or current input at 0 to 20mA. A 24V power supply can be switched out to power an external 2-Wire, 3-Wire, or 4-Wire sensor.
The MAXREFDES1152 provides a complete system solution for industry voltage and current measurement. The analog front end includes Beyond-the-Rails™ analog switches, and operational amplifiers are used to achieve voltage/ current input selection and signal conditions. The 24-bit MAX11270 analog-to-digital converter (ADC) is the heart of the system and achieves highly accurate measurements. The microcontroller communicates with the MAX11270 and the MAX7317 10-port I/O expander to control the analog front end and accept the ADC conversion results. The 24V field input power supply is isolated with the analog front end and with the microcontroller, which is powered by a USB power supply. This isolated design enhances system robustness in harsh industry applications.
The MAXREFDES1152 also integrates five Beyond-the- Rails single-pole/double throw (SPDT) analog switches (MAX14763); a dual Beyond-the-Rails 4:1 analog multiplexer (MAX14778); two ultraprecise, low-noise op amps (MAX44251); 2.75kVRMS data isolation (MAX14930 and MAX14932); an STMicroelectronics® STM32F1 microcontroller; a μp supervisory circuit (MAX6730); an FTDI Chip® USB-UART bridge; a high-efficiency iso-buck DC-DC converter (MAX17681); and isolated/regulated +5V and +3.3V power rails (two MAX16910s) and -5V power rail (MAX1697). The entire system typically operates at less than 500mW and fits into a 5cm × 10.6cm space. While targeted for industrial and PLC applications, the MAXREFDES1152 can be used in any application that requires high-accuracy analog-to-digital conversion.
Other features include:
The MAXREFDES1152 features four channels of analog input and supports voltage or current input signals with isolated power and data. The MAXREFDES1152 includes the following primary components: power supply, analog front end, ADC, and microcontroller.
The power supply generates all of the power rails used in the analog front end and ADC. The power is isolated with 24V input. The analog front end transfers the input signal to meet the ADC input range. A high-precision 24-bit ADC converts the analog input to digital signals that are read by the microcontroller. The microcontroller is isolated with the analog front end with digital isolator.
This document describes the hardware and firmware. It provides a detailed system design, especially how the analog front end is achieved. This reference design has been built and tested, details of which follow later in this document.