MAXREFDES176

Introduction

Advanced factory automation solutions (i.e., Industry 4.0) require an increasing number of smart sensors, which are typically controlled using IO-Link point-to-point serial communication between the sensor and controller (master). As a leading provider of IO-Link sensor transceiver and master transceiver ICs, Analog Devices also provides complete reference design solutions to help our customers improve their time to market. These proven designs cover all of the hardware and software requirements needed for compliance with the IO-Link standard.

Programmable logic controllers (PLCs) and distributed control systems (DCSs) use more digital inputs than any other input signal type combined. Running wires in parallel back to the PLC for industrial digital inputs is not only expensive, but also creates a wiring rat's nest that is difficult to maintain. Field buses improved the situation considerably by moving the I/O interface from the PLC to a remote I/O hub mounted close to the field sensors. However, the lack of a single, universally accepted field bus has also created confusion, training challenges, high costs, and compatibility issues among equipment.

IO-Link is the first open, field bus agnostic, low-cost, point-to-point serial communication protocol used for communicating with sensors and actuators that has been adopted as an international standard (IEC 61131-9). IO-Link finally standardizes interoperability of industrial equipment from all over the world. IO-Link can function directly from the PLC or be integrated into all standard field buses, quickly making it the defacto standard for universally communicating with smart devices like the MAXREFDES176#.

Analog Devices and TMG TE collaborated to design the MAXREFDES176# reference design that is compliant with the IO-Link version 1.1/1.0 standard. The MAXREFDES176# design consists of an industry-standard MAX22515 IO-Link device transceiver, an Atmel ATSAM low-power microcontroller that uses the TMG TE IO-Link device stack, and a MAX22192 isolated octal digital input serializer daisy-chained with a MAX22190 octal digital input serializer to provide a total of 16 digital inputs that are IEC 61131-2 compliant. The complete reference design fits on a 72mm x 54mm printed circuit board (PCB).

System Diagram

Detailed Description of Hardware

The MAXREFDES176# IO-Link digital input hub consumes minimal power, space, and cost, making it a complete solution for the many digital input sensors found in various industrial control and automation applications.

The MAX22515 IO-Link device transceiver is compliant with the IO-Link version 1.1/1.0 physical layer specification. It integrates the high-voltage functions commonly found in industrial sensors, including drivers, and two linear regulators, all in a tiny 2.5mm x 2.0mm WLP. The MAX22515 features extensive integrated protection to ensure robust communication in harsh industrial environments. All four I/O pins (V24, C/Q, DO/DI, and GND) are reverse-voltage and short-circuit protected and feature integrated ±1kV/500Ω surge protection. This enables a very small PCB area with no required external protection components, such as TVS diodes. The low on-resistance driver (C/Q) further reduces power dissipation so that this reference design consumes minimal power with very low thermal dissipation. Operation is specified for normal 24V supply voltages up to 36V. Transient protection is simplified due to high voltage tolerance (i.e., 65V absolute maximum rating for the I/O pins without the integrated TVS diodes) in addition to the integrated surge protection.

The two integrated LDO regulators in the MAX22515 generate 3.3V and 5V, reducing the number of additional external components and the required space.

The MAX22515 features a flexible control interface through either an SPI or I²C interface. In this design, we use I²C to reduce the number of pins required by the microcontroller. The I²C (or SPI) interface provides extensive diagnostics for the MAX22515, and a 3-wire UART interface is provided for IO-Link communication.

The MAXREFDES176# does not require external protection devices such as varistors or TVS diodes due to the integrated surge protection in the MAX22515 at the IO-Link interface. This reference design meets both IEC 61000-4-2 for electrostatic discharge (ESD) up to ±4kV and IEC 61000-4-4 for electrical fast transient (EFT) ±4kV standards. It is designed to meet a surge capability (2A at t = 1.2/50μs) up to ±1.0kV.

The MAXREFDES176# uses an industry-standard M12 connector, which allows a 4-wire cable to be used.

The MAX22192 is an IEC 61131-2 compliant industrial digital input device with integrated digital isolation. The MAX22192 translates eight 24V, current-sinking industrial inputs to an isolated, serialized SPI-compatible output that interfaces with a 1.71V to 5.5V logic voltage. A current-setting resistor allows the MAX22192 to be configured for Type 1/Type 3 or Type 2 inputs. The MAX22192 has an isolation rating of 600VRMS for 60 seconds and is available in a 70-pin GQFN package with 2.3mm clearance and creepage.

The MAX22190 is also an IEC 61131-2 compliant industrial digital input device, but without integrated isolation. The MAX22190 translates eight 24V, current-sinking industrial inputs to a serialized SPI-compatible output that is daisy-chained with the MAX22192. A current setting resistor allows the MAX22190 to be configured for Type 1/Type 3 or Type 2 inputs.

A LATCH signal on each digital input chip allows for synchronizing input data across both devices.

The Atmel microcontroller limits the reference design operating temperature range to -40°C to +105°C. However, the MAX22515 IO-Link transceiver, MAX22192, and MAX22190 can all operate over the -40°C to +125°C temperature range.

The MAXREFDES176# consumes 30mA (typ). A green LED indicates the 3.3V alive signal from the MAX22515, and 16 green LEDs are used to indicate the status of each digital input.

For detailed information on the digital input devices please refer to MAX22190 and MAX22192 data sheets.

Non-Isolated vs. Fully Isolated Mode of Operation

The MAXREFDES176# can be operated in two different isolation modes depending upon whether RI1 and RI2 (both 0Ω resistors) are installed (non-isolated) or not (fully isolated). In non-isolated mode, power (+24V) is provided from the IO-Link master through pin 1 of the X1 connector. In fully isolated mode, two power domains and two power sources are required. For the "IO-Link Side" (as seen in Figure 1), the IO-Link master provides power (+24V) through pin 1 of the X1 connector. For the "Field Side," an external 24V supply is required, which is connected through terminal T7.

The MAX17621C current limiter is used to provide overvoltage (OV) and reverse-voltage protection for the external supply, blocking any current flowing in the reverse direction and providing protection for the circuit. In this reference design, a SMAJ33CA TVS was included for surge protection.

Detailed Description of Firmware

The MAXREFDES176# ships preprogrammed as a working IO-Link device ready to connect to an IO-Link master. The firmware targets an Atmel ATSAM microcontroller and follows the simple flowchart shown in Figure 2. The firmware utilizes the TMG TE IO-Link device stack. After plug-in, the MAXREFDES176# waits for a wake-up signal from the IO-Link master. Once the wake-up signal is received, the MAXREFDES176# synchronizes to the IO-Link master using the 230.4kbps (COM3) baud rate, and communication parameters are exchanged. The IO-Link master then starts a cyclic data exchange by requesting the sensor process data. If the MAXREFDES176# is removed, the IO-Link master detects a missing sensor.

The TMG TE IO-Link Device Tool software is Windows^®-compatible and features IODD file import capability, connects to a PC through USB, and is available to download from the TMG TE website.

The TMG TE IO-Link Device Tool software is shown in Figure 3, and a complete guide is also downloadable from the TMG TE website.

Source code for the MAXREFDES176# is not available. The TMG TE IO-Link stack ships preprogrammed inside the MAXREFDES176# hardware with a perpetual license.

The TMG TE contact information is as follows:

Technologie Management Gruppe

Technologie und Engineering GmbH
Zur Giesserei 10
76227 Karlsruhe
Germany
Phone: +49 7218 28060
E-Mail: willems@tmgte.de
Internet: www.tmgte.com

Detailed Description of Software

The MAXREFDES176# was verified using the MAXREFDES165# IO-Link Master, featuring the MAX14819 IO-Link master transceiver and the IODD interpreter tool IO-Link Device Tool from the TMG TE website.

Download the IODD file (*.xml) located in the Design Resources tab and follow the step-by-step instructions in the Quick Start Guide section on how to use the software. Figure 3 shows a screenshot of the TMG TE IO-Link Device Tool communicating with the master and sensor.

EMC Testing

The general rules for the test configuration of a device (such as the MAXREFDES176#) are as follows:

• The SDCI cable shall be unshielded, 20m long, coiled, and placed 10cm (4in) above the ground plane.
• The devices shall be placed 10cm (4in) above the ground plane.

The MAXREFDES176# was tested in an Analog Devices lab for the common industrial compliance standards, and the test methodology and results are presented in this document. Although the IO-Link Interface and System Specification does not require surge testing, Analog Devices did this test in addition to the ESD and EFT tests.

Equipment Used

• MAXREFDES176# IO-Link Sensor
• MAXREFDES165# 8-Port IO-Link Master
• 20m M12 Cable
• Haefely^® Technology ECOMPACT4 EFT/Surge Generator
• Teseq^® CDN 117 Signal Line Coupling Network
• Teseq CDN 3425 EFT Data Line Coupling Clamp
• Teseg NSG438 ESD Generator
• 24V DC Power Supply

Surge Testing

The MAXREFDES176# module was tested to withstand up to ±1.0kV of 1.2/50µs IEC 61000-4-5 surge with a total source impedance of 500Ω. Surge testing was performed using the MAXREFDES165# IO-Link master, and 10 surge pulses were applied for each test as shown in Table 1.

While communicating with the master during the tests shown in Table 1, the MAXREFDES176# continued to operate normally (execute code and transfer data) and was not damaged by the tests, and the MAX22515 registers were not corrupted.

EFT/Burst Testing

Using a 20m IO-Link cable with standard M12 connectors, the MAXREFDES176# was tested to withstand electrical fast transient (EFT)/bursts up to ±4kV according to IEC 61000-4-4. EFT testing was performed using the MAXREFDES165# IO-Link master, and EFT pulses were applied for one minute for each test, as shown in Table 2.

Repetition rates of 5kHz and 100kHz were tested, along with burst lengths of 15ms and 0.75ms. The MAXREFDES176# was not damaged by the test, and the MAX22515 registers were not corrupted.

Figure 6 shows the test setup for the EFT and surge tests according to IEC 61000-4-4 and IEC 61000-4-5.

Due to test equipment limitations, we were unable to count M-sequence errors. To validate whether the microcontroller on the MAXREFDES176# was susceptible to EFT, it was programmed to generate square-wave outputs to toggle the C/Q and DO pins. On the square wave, disturbances that imply communication errors were not detected (i.e., the high and low levels were always within their range).

It was clear that the MAX22515 did not go through a reset, because the reset settings of the MAX22515 would have disabled the C/Q output driver. Additionally, the microcontroller firmware was set up to toggle C/Q very fast every time the microcontroller was reset (Figure 7). This clearly indicates if a reset occurred on the microcontroller, which also causes the MAX22515 registers to be re-initialized by the microcontroller. The pass/fail test criteria were that the high/low levels were not disturbed, and no fast toggling was observed.

Figure 7 shows the test setup for the EFT and surge tests according to IEC 61000-4-4 and IEC 61000-4-5.

ESD Testing

The MAXREFDES176# was tested to withstand electrostatic discharge (ESD) for Contact and Air-Gap Discharge up to ±4kV according to IEC 61000-4-2. ESD testing was performed on the MAXREFDES176# M12 connector pins after the test operation was verified using the MAXREFDES165# IO-Link master to transfer data, as shown in Table 3. The MAXREFDES176# was not damaged by any ESD tests and continued to operate normally.

Note that the IO-Link Interface and System Specification Version 1.1.2 requires ESD testing with a 20m cable attached, and the ESD strike is applied to the sensor casing. Because this reference design is only a PCB with no metallic casing, the ESD strikes were applied to the male M12 connector pins. Analog Devices expects this design to meet the levels specified in Table 3 when testing with a casing and cable.

Restrictions and Warnings for Analog Devices Reference Design Use

The MAXREFDES176# is designed and tested to meet IO-Link operation and harsh industrial environments covered by IEC 61000-4-x standards for transient immunity. This board and associated software are designed to be used to evaluate the performance of the MAX22515, but are not intended to be deployed as-is into an end product in a factory automation system.

The MAXREFDES176# is not for use in functional safety or safety-critical systems.

Quick Start Guide

To test the MAXREFDES176# sensor, connect it to a port of an IO-Link master. In the following example, a MAXREFDES165# IO-Link master and TMG software tool are used, but any IO-Link compliant master and associated IO-Link device GUI should work.

Required Equipment

Supplied by Analog Devices

• MAXREFDES176#

Note: Download files from the Design Resources tab.

User Supplied

• IO-Link master (i.e., MAXREFDES165#) with a 24V AC-to-DC power adapter
• TMG TE IO-Link Device Tool software
• One IO-Link cable
• Windows 7, Windows 8, or Windows 10 PC with a USB port

Master Setup Procedure

1. Connect the MAXREFDES176# sensor to the IO-Link master with an IO-Link M12 cable.
2. Connect the IO-Link master to the PC with a USB cable.
3. Download and install the latest IO-Link Device Tool software from the TMG TE website.
4. Download the IODD file for the MAXREFDES176# from the Design Resources tab or from the TMG TE website.
5. The MAXREFDES176# comes preprogrammed with firmware and the IO-Link device stack.

Sensor Testing Procedure

1. Connect the female end of the IO-Link cable to the MAXREFDES176#.
2. Connect the male end of the IO-Link cable to one of the ports on the IO-Link master.
3. Open the IO-Link Device Tool software and press Search Master as seen in Figure 3. Select the 4-port master (MAXREFDES165#), which the tool finds.
4. Import the IODD file for the MAXREFDES176#. This includes a picture of the PCB, as shown in Figure 9.
5. Press Go Online, as shown in Figure 3.
6. If communication is established correctly, the IO-Link Device Tool software shows the IO-Link master connection. Select the port number that the MAXREFDES176# is connected to and press Check Devices below the Ports section. When the software shows that MAXREFDES176# is connected, press Takeover devices into engineering in the Check Devices window, as shown in Figure 10.
7. The Go Offline button is green, and the software tool shows that the device is MAXREFDES176# and the IODD vendor is TMG TE GmbH, as shown in Figure 11.
8. Double-click port 3 (for this example) to open the window showing MAXREFDES176# sensor details, and then select the Process Data tab.
9. Apply a trigger to the digital input channels (connect the Dx input to +24V) to see the 16 bits (one for each channel), and observe how they change from 0 to 1 when a particular channel is at logic high. In this test, input channel D9 is driven logic high and the GUI shows the true (logic-high) setting, as shown in Figure 12.

Trademarks List

Atmel is a registered trademark and registered service mark of Atmel Corporation.
Haefely is a registered trademark of Haefely Test AG.
IO-Link is a registered trademark of Profibus User Organization (PNO).
Maxim is a registered trademark of Maxim Integrated Products, Inc.
Teseq is a registered trademark of Ametek CTS.
Windows is a registered trademark of Microsoft Corporation.