MAXREFDES1152: Quad general-purpose analog input based on the MAX11270

The MAXREFDES1152 is a four-channel general-purpose analog input for measuring voltage or current signals. Each channel can be configured as a 0 to 10V voltage input or a 0 to 20mA current input. Lead to 24V power supply to power external 2-wire, 3-wire or 4-wire sensors.

MAXREFDES1152 provides a complete system solution for industrial voltage and current measurements. The analog front end includes Beyond-the-Rails™ analog switches that utilize operational amplifiers for voltage/current input selection and signal conditioning. The MAX11270 24-bit analog-to-digital converter (ADC) is the core device of the system and enables high-precision measurements. The microcontroller communicates with the MAX11270 and MAX7317 10-port I/O expanders to control the analog front end and receive the ADC conversion results. The 24V field input power is isolated from the analog front end and microcontroller, which are powered by USB power. This isolation design increases system reliability in harsh industrial applications.

MAXREFDES1152 also integrates five over-the-rail single-pole double-throw (SPDT) analog switches (MAX14763); a dual-channel over-the-rail 4:1 analog multiplexer (MAX14778); and two ultra-high-precision, low-noise operational amplifiers (MAX44251) ; 2.75kVRMS data isolators (MAX14930 and MAX14932); STMicroelectronics® STM32F1 microcontroller; μp supervisory circuit (MAX6730); FTDI Chip® USB-UART bridge; high-efficiency, iso-buck DC-DC converter (MAX17681); and + 5V and +3.3V isolated/regulated power supplies (2 MAX16910s) and -5V power converters (MAX1697). The entire system consumes less than 500mW and is installed in a 5cm × 10.6cm space. When used in industrial and PLC applications, the MAXREFDES1152 supports any application requiring high-precision analog-to-digital conversion.

The MAXREFDES1152 has four analog input channels, supports voltage or current input signals, and provides power and data isolation. The MAXREFDES1152 includes the following main units: power supply, analog front end, ADC, and microcontroller.

The power supply generates all supply voltages required by the analog front end and ADC. The power supply is isolated from the 24V input. The analog front end converts the input signal to meet the ADC input range. A 24-bit high-precision ADC converts the analog input into a digital signal, which is read by the microcontroller. Use digital isolators to isolate the microcontroller from the analog front end.

Key Features

• High-precision measurement

• 0 to +10V voltage input

• 0 to 20mA current input

• Four channels

• Each channel can be configured as voltage or current input

• 24V input protection

• Power and data isolation

• Board calibration

• Connector provides 24V output

• 24V output can be enabled or disabled

This circuit board is not for sale.

Design, build and test

This document describes the hardware and firmware and provides detailed system design, specifically how to implement the analog front end. The reference design has been built and tested, please refer to this document for details.

design resources