MAXREFDES176#: IO-Link 16-Channel Digital Input Hub
The MAXREFDES176# is a complete, IO-Link® 16-channel digital input hub reference design that consists of a MAX22515 IO-Link transceiver with integrated protection. It demonstrates an isolated digital input hub using the MAX22192 isolated octal digital input device daisy-chained with the MAX22190 octal digital input device to provide a total of 16 digital input channels.
Type 1 and Type 3 sensors are supported by default. Type 2 sensors can also be supported by modifying the resistor value that controls the value of the current sink within the devices. Built in an industrial form factor, the MAXREFDES176# uses an industry-standard M12 connector, allowing a 4-wire cable to be used. The digital input channels use industry-standard PCB terminal blocks.
In this design, an Atmel® ATSAM low-power microcontroller interfaces between the MAX22192 isolated digital input serializer and the MAX22515 IO-Link device transceiver. The MAX22515 features integrated surge protection for robust communication in a very small PCB area without requiring external protection components, such as TVS diodes. The MAX22515 is available in a tiny 20-bump WLP package, allowing the MAXREFDES176# to have a small footprint, though this is mostly determined by the size of the connectors. The design is reverse-polarity protected using the integrated active reverse-polarity protection of the MAX22515. The MAX22515 has two integrated LDO regulators (3.3V and 5.0V). The 3.3V LDO is used to generate the 3.3V supply for other circuitry, reducing the number of required external components and further saving space. The MAX22515 also features low on-resistance drivers (C/Q and DO/DI) to reduce power dissipation, allowing this reference design to consume minimal power with very low thermal dissipation.
This IO-Link device utilizes the Technologie Management Gruppe Technologie und Engineering (TMG TE) IO-Link device stack to communicate to any IO-Link version 1.1-compliant master. The board contains a male M12 connector for connecting to a compliant IO-Link master using a standard M12 cable. Connecting the MAXREFDES176# to a USB IO-link master, such as the MAXREFDES165#, with the associated software allows for easy evaluation.
Design files, firmware, and software are available on the Design Resources tab. The board is also available for purchase.
- IEC 61131-9 Compliant
- TMG TE IO-Link Stack
- IO-Link Version 1.1 Compliant
- Integrated Galvanic Isolation
- On-Chip Serialization
- Industrial Automation
- Digital Input Modules
- PLC and DCS Systems
- Smart Sensors
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, Maxim Integrated® 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#.
Maxim Integrated 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).
Figure 1. MAXREFDES176# system block 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.
Figure 2. The MAXREFDES176# firmware flowchart.
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.
Figure 3. The TMG TE IO-Link Device Tool.
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
Detailed Description of Software
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.
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 a Maxim Integrated 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, Maxim Integrated did this test in addition to the ESD and EFT tests.
- 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
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.
Table 1. Surge Test Results
|Test Condition||Surge Tests|
|L+ TO GND||C/Q TO GND||L+ TO CQ|
Figure 4. Surge testing setup.
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.
Table 2. EFT/Burst Test Results
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 5. Test setup for fast transients (device).
Figure 6 shows the test setup for the EFT and surge tests according to IEC 61000-4-4 and IEC 61000-4-5.
Figure 6. EFT/burst testing bench setup.
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.
Figure 7. C/Q and DO toggling with microcontroller reset.
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.
Table 3. ESD Test Results
|Test Condition||L+ TO GND||C/Q TO GND|
|+4kV Contact Discharge||Pass||Pass|
|-4kV Contact Discharge||Pass||Pass|
|+4kV Air-Gap Discharge||Pass||Pass|
|-4kV Air-Gap Discharge||Pass||Pass|
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. Maxim Integrated expects this design to meet the levels specified in Table 3 when testing with a casing and cable.
Figure 8. ESD testing setup.
Restrictions and Warnings for Maxim Integrated 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.
Supplied by Maxim
Note: Download files from the Design Resources tab.
- 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
Trademarks ListAtmel 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.
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