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MAXREFDES185# Configurable IO with Safety Monitoring

MAXREFDES185

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Description

The MAXREFDES185# is a complete, universal input-output (UIO) reference design with Safety Monitoring of all IO signals. It demonstrates a fully software-configurable UIO module (analog IO + digital IO on a common pin) using the MAX22000 industrial configurable analog IO device and the MAX14914A low-leakage digital IO device. The industry-standard four-way PCB terminal block includes support for temperature measurement using a resistance temperature detector (RTD) or a thermocouple, including built-in cold-junction compensation for thermocouple measurements.

The MAXREFDES185#, built in an industrial form-factor (Figure 1), uses an industry-standard Pmod connector with a 3.3V power supply. A barrel connector supports an external 24V DC input, from which higher voltage HVDD and HVSS rails are generated. The complete reference design fits on a 75mm x 20mm printed circuit board (PCB).

The configurable modes include an analog voltage input (0 to +10V), an analog current input (0 to +20mA), an analog voltage output (0 to +10V), and an analog current output (0 to +20mA), as well as a digital input (IEC 61131-2 Types 1, 2 or 3) and a digital output (0-24V, up to 1.3A) across the UIO and GND terminals. The accuracy is as good as 0.1% FSR over a ±50°C temperature variation. The other two terminals can be configured to measure temperature using a standard device such as a PT100 or PT1000 RTD.

The MAX14914A is a pin-controlled low-DOI-leakage version of the MAX14914, designed to work seamlessly with the MAX22000 for universal IO (UIO) applications. The MAX14914A features full IEC 61131-2 compliance in both DO and DI modes of operation. The MAX14914A provides monitoring of the DOI output in both high-side and push-pull modes and the corresponding logic level can be seen through the inversed DOI_LVL logic output.

The MAX22005 is a 12-channel industrial-grade analog-input IC that can operate in voltage or current mode. For this design, the MAX22005 has channels configured to monitor all the analog signals from the MAX22000 no matter if it is operating as an analog input or analog output (voltage or current mode) in addition to monitoring the temperature measurement sensor.

Features

  • Universal Analog IO
  • Safety Monitoring
  • IEC 61131-2 Compliant
  • Power Tracking

Application

  • Industrial Automation
  • Universal Input Output Modules
  • PLC and DCS Systems
  • Smart Sensors and Actuators

  • MAXREFDES185 Photo

    MAXREFDES185 Photo

  • MAXREFDES185 Side Photo

    MAXREFDES185 Side Photo

 

Schematic

schematic

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PCB Layout

pcb-layout

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All Design Files

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BOM

bom

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Fab Assembly

Details Section

Details Section

Introduction

Advanced factory automation (Industry 4.0) solutions require an increasing number of smart sensors and smart actuators, which are typically controlled using programmable logic controllers (PLCs) or distributed control systems (DCS). However, with a broad range of legacy sensors and actuators already deployed, system engineers also require IO modules with extra flexibility which can be software-configured rather than requiring extensive in-situ rewiring or manual configuration. A UIO module, as shown in the MAXREFDES185#, provides full software configurability for all common analog and digital IOs without requiring a field engineer to change the field wiring or IO module.

Maxim Integrated, as a leading provider of configurable IO ICs, also provides complete reference design solutions to help its customers improve their time-to-market. These proven designs cover all the hardware and software requirements needed for compliance with the analog and digital IO interfaces.

A true field-configurable, UIO is realized when the field programmability of a module is combined with a software-configurable IO. Industrial sensor/actuator OEMs provide end-users total flexibility at the factory-floor level to simplify equipment installation and commissioning, while reducing their number of SKUs and BOMs, thereby simplifying and streamlining purchasing and manufacturing.

The MAX22000 industrial universal analog IO device is fully software-configurable for all common industrial analog input and output, voltage and current ranges. The MAX14914A is a pin-controlled low-DOI-leakage version of the MAX14914, designed to work seamlessly with the MAX22000 for UIO applications. The MAX14914A features full IEC 61131-2 compliance in both DO and DI modes of operation. The MAX22005 is a 12-channel industrial-grade analog-input IC. This design is used to monitor all analog IO signals from the MAX22000, in addition to monitoring the temperature measurement sensor. The complete reference design fits on a 75mm x 20mm printed circuit board (PCB).

The configurable modes include analog voltage input (0 to +10V), analog current input (0 to +20mA), analog voltage output (0 to +10V), and analog current output (0 to +20mA), as well as digital input (IEC 61131-2 Types 1, 2 or 3) and digital output (0-24V, up to 1.3A) across the UIO and GND terminals. The MAXREFES185# sets the linear range at 105% and the full-scale range at 125% of the nominal range. The accuracy is as good as 0.1% FSR over a ±50°C temperature variation. The reference design comes with an industry-standard 4-pin terminal block. In addition to the UIO terminal, the other two terminals can be configured to measure temperature using a standard device such as a PT100 or PT1000 RTD. These terminals interface to the integrated programmable gain amplifier (PGA) in the MAX22000 at inputs AI5 and AI6.

For this design, the MAX22005 has channels configured to monitor all the analog voltage and current signals from the MAX22000, in addition to monitoring the temperature measurement sensor. The other channels of the MAX22005 are used to monitor the two power-supply rails (HVDDO and HVSSO) as well as include an on-board PT1000 sensor located near the four-way terminal block. This is used for cold-junction compensation with thermocouple measurements.

In addition to DIO modes of operation, the MAX14914A monitors the DOI output in both high-side and push-pull modes. The corresponding logic-level can be seen through the inversed DOI_LVL logic output. The DOI_LVL is read from a MAX22000 GPIO, which provides safety monitoring for the MAX14914A.

The Pmod connector interfaces between the two SPI ports (for MAX22000 and MAX22005) using independent CS signals, CS1 and CS2. The MAXREFDES185# can be controlled using a simple USB-to-SPI adapter such as the USB2PMB2# (with associated GUI) or connected to a microcontroller or FPGA board with the necessary software to control the board. Both the MAX22000 and MAX22005 have a SYNCH pin, which allows the host to synchronize data conversion cycles, ensuring the two measurements are consistent from each of the 24-bit delta-sigma ADC cores found in each IC. The RDY signal from each IC is fed back to the host to indicate conversion completion. Both the MAX22000 and MAX22005 have general-purpose input/output (GPIO) pins which are useful for controlling other functions on the PCB, while simplifying the system interface to a simple SPI port. The GPIO pins from the MAX22000 control the MAX14914A, which allows full software configurability of this device. This includes Type 1/3 or Type 2 digital input operation or high-side or push-pull digital output.

High-efficiency buck converters generate different voltage rails from the 24V DC input source. A MAX17651 generates HVDD which is nominally a +24V supply. A MAX17532 generates the adjustable output supply, HVDDO_ADJ, with five presettable levels from 4.2V to 24V, which were selected using GPIO pins from the MAX22005. This controls external FETs to switch in different feedback resistors to the MAX17532. This power-tracking feature minimizes output power dissipation, reducing heat generated within the module.

System Diagram

Figure 2. MAXREFDES185# system block diagram.

Detailed Description of Hardware

The MAXREFDES185# UIO design consumes minimal power, space, and cost—making it a complete solution for the many input sensors or output actuators found in various industrial control and automation applications.

The ICs used in MAXREFDES185# feature a robust analog front-end with high-voltage protection up to ±36V for all analog input ports. A combination of 5kΩ input resistors for all analog inputs and an additional TVS diode on the UIO terminal allows this design to meet common industrial transient immunity specifications. This reference design meets both the IEC 61000-4-2 for electrostatic discharge (ESD) up to ±4kV and is designed to meet a surge capability (t = 1.2/50μs) up to ±2.0kV.

The MAX22000 is an industrial-grade configurable analog input/output device configurable on-the-fly in software as a voltage/current input or output. Additional inputs are available to measure other analog signals. The device offers an 18-bit DAC with a fast settling time as well as a 24-bit delta-sigma ADC. The ADC and DAC can individually choose between an internal or an external reference. This design uses the internal voltage reference. The MAX22000 can meet an accuracy of 0.1% FSR over a ±50°C temperature variation because of the very stable 5ppm/°C internal reference. The MAX22000 sets the linear range at 105% and the full-scale range at 125% of the nominal range. For example, the MAX22000 provides a linear range of ±10.5V and a full-scale range of ±12.5V for a nominal range of ±10V. The MAX22000 supports the ADC with a low-noise PGA with high-voltage and low-voltage input ranges to support RTD measurements. Additional auxiliary inputs are also present but are not used in this design.

The MAX22000 communicates through a high-speed SPI bus for all configuration and management information as well as conversion results. An optional 8-bit CRC enhances the reliability of the SPI interface, protecting against up to 8-bit bursts as well as all double-bit errors. The MAX22000 operates from 2.7V to 3.6V analog and digital supplies, and up to ±24V high-voltage supplies. The device is available in a 64-pin LGA package and operates over the -40°C to +125°C industrial temperature range.

The MAX22005 is an industrial-grade configurable analog input device configurable on-the-fly in software. The MAX22005 provides 12 single-ended, six differential, four configurable inputs, or any combination thereof. The device offers a 24-bit delta-sigma ADC, multiplexers, and high-voltage zero-drift input amplifiers covering all standard industrial voltage and current ranges. The MAX22005 has a best-in-class performance and can meet an accuracy of 0.05% FSR over a ±50°C temperature variation with factory calibration.

The MAX22005 communicates through a high-speed SPI bus for all configuration and management information as well as conversion results. An optional 8-bit CRC enhances the reliability of the SPI interface, protecting against up to 8-bit bursts as well as all double-bit errors. The MAX22005 operates from 2.7V to 3.6V analog and digital supplies, and up to ±24V high-voltage supplies. The device is available in a 48-pin LGA package and operates over the -40°C to +125°C industrial temperature range.

The MAX14914 is a high-side/push-pull driver that operates as both an industrial digital output (DO) and an industrial digital input (DI). The MAX14914A is a low-DOI-leakage version of the MAX14914, designed to work together with the MAX22000 industrial configurable analog IO device.

The MAX14914A is fully IEC 61131-2-compliant in both their DO and DI modes of operation. The high-side switch current limit is resistor-settable from 135mA (min) to 1.3A (min). For this design, the default current limit is set at 500mA with R155 = 82.5kΩ. To change the current limit, select a different resistor value as described in the MAX14914A datasheet. The high-side driver's on-resistance is 120mΩ (typ) at 125°C ambient temperature. The optional push-pull operation allows the driving of cables and fast discharge of load capacitance. The output voltage is monitored and indicated through the DOI_LVL pin for safety applications. The MAX14914A complies with Type 1, Type 2, or Type 3 input characteristics when configured for DI operation. The MAX14914A operates from a 24V field supply and has a logic interface supply input of 2.5V to 5.5V to allow easy interfacing to a range of microcontroller or FPGA devices. The device is available in a 16-pin TQFN package and operates over the -40°C to +125°C industrial temperature range.

Galvanic isolation is not supported with this design. If the USB2GPIO# adapter is used, the USB2GPIOISO# module can be used to implement data isolation featuring the MAX14483 digital isolator.

All Maxim ICs used in this design operate over the -40°C to +125°C temperature range. Refer to the MAX22000, MAX22005, and MAX14914A datasheets for detailed information on the software-configurable IO devices.

Power Supplies

Power solutions use Maxim Integrated ICs and modules to generate the various voltage rails (Figure 2). Power is supplied from an external 24VDC adapter (20V to 33V range) via a barrel connector. Multiple high-efficiency buck converters are used to step down this 24V rail. A MAX17651 generates HVDD, which is nominally the +24V supply. A MAX17532 generates the adjustable output supply, HVDDO_ADJ, with five pre-settable levels from 4.2V to 24V, which are selected using GPIO pins from the MAX22005 (signals PS_SEL[1:3]). This controls external FETs to switch in different feedback resistors to the MAX17532 to provide discrete levels as listed in Table 1. This power-tracking feature minimizes output power dissipation, reducing heat generated within the module. The MAXREFEDES185# GUI automatically calculates HVDDO and sets the appropriate FETs based on the operating mode (analog voltage output) and sets the voltage setting (volts) to ensure a minimum of 3V headroom between the HVDDO_ADJ and the output voltage. For all other operating modes, the HVDDO_ADJ default is 24V. If MAXREFDES185# is used with an external microcontroller, the firmware needs to determine the appropriate HVDDO_ADJ level and sets the supply-voltage-selecting FETs as required.

Table 1. Power Tracking Options

PS_SEL3 PS_SEL2 PS_SEL1 HVDDO_ADJ (V)
0 0 0 4.2
0 1 0 9
0 0 1 14
0 1 1 19
1 0 0 24-28

The MAXREFDES185# consumes 10mA (typ) under normal conditions but uses more if the current input or output mode is selected. A green LED (LED202) indicates the presence of an external supply.

Universal IO Terminal Block

The MAXREFDES185# supports several use modes depending upon both software configuration and the setting of jumpers JP1 and JP2 as described in Table 2.

Without the two shunts installed, the MAXREFDES185# operates in 2-wire mode, and with the two shunts installed, it operates in 4-wire mode. While operating in 2-wire mode, temperature measurements are supported with a sensor connected to SNS+ and SNS-.

Table 2. Jumper Options

Jumper Shunt Position Description
JP1 Open* UIO connected to MAX22000 AI and AO ports, SNS+ connected to AI5
Closed SNS+ connected to UIO
JP2 Open* SNS- connected to AI6
Closed SNS- connected to GND


* Default position.

Detailed Description of Software

The MAXREFDES185# can be verified using a USB-to-SPI adapter, such as the USB2PMB2#, with the associated GUI software which can be downloaded from the Design Resources tab. Alternatively, the user can take the code examples and write software for their target microcontroller or FPGA.

Download the MAXREFDES185# GUI located in the Design Resources section. Follow the step-by-step instructions in the Quick Start Guide section to use the software.

The MAXREFDES185# GUI has two main tabs for different modes of operation and monitoring – Universal IO and Analog Input.

Universal IO Tab

The main modes are all accessed from the Universal IO tab which is shown in Figure 3. The drop-down menu allows the user to select between the analog or digital, input or output configurations utilizing the MAX22000 and the MAX14914A. Depending upon the mode selected, the GUI includes a simplified block diagram with the relevant connections highlighted.

Figure 3. MAXREFDES185# GUI – Universal IO tab.

Analog Input Tab

The Analog Input tab shown in Figure 4 is dedicated to reading data from the MAX22005 and comparing it to the original data from the MAX22000. Both the MAX22000 and MAX22005 measurements are shown in units (V or mA) or as a hex value to provide an easy correlation between the two ADC cores. The multiple variables monitored by the MAX22005 for the 4-way terminal block are shown for voltage and current.

Figure 4. MAXREFDES185# GUI – Analog Input tab.

Automatic Calibration

The Universal IO tab includes a button for automated calibration, which brings up a screen as shown in Figure 5. Full details of how to use this procedure are included in the Quick Start Guide.

Figure 5. MAXREFDES185# GUI – Automated Calibration.

Analog IO Accuracy and Monitoring

The MAXREFDES185# was calibrated using the MAXREFDES185# GUI leveraging the factory calibrated MAX22005, and tested at room temperature to show the accuracy of the MAX22005 in monitoring the MAX22000 input.

For voltage mode, the GUI UIO tab was used to set the output voltage (stepping from 0V to 12.5V in 0.5V steps), and the Analog IO tab was used to log the voltage values read by the MAX22000 and MAX22005. An Agilent 34401A 6.5-digit DMM was also used to measure the output voltage. Figure 6 demonstrates the high degree of accuracy of both devices, well within the 0.02% FSR at room temperature, and the correlation of the MAX22005 to the MAX22000.

Figure 6. MAXREFDES185# voltage measurement accuracy.

For current mode, the GUI UIO tab was used to set the output current (stepping from 0mA to 25mA in 1mA steps), and the Analog IO tab was used to read the current values read by the MAX22000 and MAX22005. An Agilent 34401A 6.5-digit DMM was also used to measure the output current. Figure 7 demonstrates the high degree of accuracy of both devices, well within the 0.02% FSR at room temp, and the correlation of the MAX22005 to the MAX22000.

Figure 7. MAXREFDES185# current measurement accuracy.

For temperature measurement, a Fluke 724 calibrator was used to simulate a PT100 RTD sensor, while the GUI UIO tab was used to measure the temperature. The Fluke 724 calibrator was used to record data between -200°C and +450°C. Figure 8 demonstrates the accuracy of the MAX22000 to within 1°C from -100°C to +300°C and well within the 0.02% FSR at room temperature.

Figure 8. MAXREFDES185# RTD measurement accuracy.

EMC Testing

The MAXREFDES185# was tested in a Maxim Integrated lab using common industrial compliance standards. The test methodology and results are presented in this document.

Equipment Used:

  • MAXREFDES185#
  • USB2PMB2# adapter
  • Teseq® EFT/Surge Generator
  • Teseq NSG438 ESD Generator

Surge Testing

The MAXREFDES185# module was tested to withstand up to ±1.0kV of 1.2/50µs IEC 61000-4-5 surge with a total source impedance of 42Ω. The surge testing was performed using ten surge pulses, which were applied for each test.

The MAXREFDES185# continued to operate normally and was not damaged by the tests. The MAX22000 and MAX22005 registers were not corrupted while communicating with the host adapter during the tests shown in Tables 3 and 4.

Table 3. Surge Test Results for the UIO Interface Line-to-Ground

Test Condition Surge Tests
UIO TO GND SNS+ TO GND SNS- TO GND
+1kV Pass Pass Pass
-1kV Pass Pass Pass

Table 4. Surge Test Results for the UIO Interface Line-to-Line

Test Condition Surge Tests
UIO TO SNS+ UIO TO SNS- SNS+ TO SNS-
+1kV Pass Pass Pass
-1kV Pass Pass Pass

ESD Testing

The MAXREFDES185# was tested to withstand electrostatic discharge (ESD) for Contact and Air-Gap Discharge up to ±4kV according to IEC 61000-4-2. The ESD testing was performed on the MAXREFDES185# UIO port-to-ground at the field connection terminal block. Functional operation after the test was verified using the USB2PMB2# adapter and the MAXREFDES185# GUI to transfer data (Table 5). The MAXREFDES185# was not damaged by any ESD tests and continued to operate normally.

TEST CONDITION UIO TO GND SNS+/SNS- TO GND
+4kV Contact Discharge Pass Pass
-4kV Contact Discharge Pass Pass
+4kV Air-Gap Discharge Pass Pass
-4kV Air-Gap Discharge Pass Pass

Table 5. ESD Test Results

Restrictions and Warnings for Maxim Integrated Reference Design Use

The MAXREFDES185# is designed and tested to meet harsh industrial environments covered by the IEC 61000-4-x standards for transient immunity. This board and associated software are designed to evaluate the performance of the MAX22000, MAX14914A, and MAX22005 but are not intended to be deployed as-is into an end product in a factory automation system.

The MAXREFDES185# is not for use in functional safety or safety-critical systems.

Maxim Devices (6)

Part Number Name Product Family Order Design kits and evaluation modules
MAX22000 Industrial Configurable Analog I/O Digital-to-Analog Converters Buy Now
MAX14914A High-Side Switch with Settable Current-Limiting, Push-Pull Driver Option, and Digital Input Configuration MOSFET Drivers and Controllers Buy Now
MAX22005 12-Channel Factory-Calibrated Configurable Industrial-Analog Input Analog-to-Digital Converters Buy Now
MAX17651 4V to 60V, 100mA, Ultra-Low Quiescent Current, Linear Regulator Linear Regulators (LDOs) Buy Now
MAX17532 42V, 100mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter with 22µA No-Load Supply Current Switching Regulator - Switching Regulators Buy Now
MAXM17552 4V to 60V, 100mA, Compact Step-Down Power Module Switching Regulator - Switching Regulators Buy Now

Maxim Devices (6)

Part Number Product Family
Digital-to-Analog Converters
Industrial Configurable Analog I/O
MOSFET Drivers and Controllers
High-Side Switch with Settable Current-Limiting, Push-Pull Driver Option, and Digital Input Configuration
Analog-to-Digital Converters
12-Channel Factory-Calibrated Configurable Industrial-Analog Input
Linear Regulators (LDOs)
4V to 60V, 100mA, Ultra-Low Quiescent Current, Linear Regulator
Switching Regulator - Switching Regulators
42V, 100mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter with 22µA No-Load Supply Current
Switching Regulator - Switching Regulators
4V to 60V, 100mA, Compact Step-Down Power Module

Design Files (6)

Title Type Size Date
MAXREFDES185 Schematic PDF 305KB 2021-07-29
MAXREFDES185 BOM CSV 8KB 2021-07-29
MAXREFDES185 Fab Assembly ZIP 3MB 2021-08-10
MAXREFDES185 PCB PDF 1MB 2021-07-29
MAXREFDES185 All Design Files ZIP 2MB 2021-07-29
MAXREFDES185# Quick Start Guide PDF 1MB 2021-07-19
Date Type
2021-07-29

MAXREFDES185 Schematic

(PDF, 305KB)

2021-07-29

MAXREFDES185 BOM

(CSV, 8KB)

2021-08-10

MAXREFDES185 Fab Assembly

(ZIP, 3MB)

2021-07-29

MAXREFDES185 PCB

(PDF, 1MB)

2021-07-29

MAXREFDES185 All Design Files

(ZIP, 2MB)

2021-07-19

MAXREFDES185# Quick Start Guide

(PDF, 1MB)

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