MAXREFDES27

Detailed Description of Hardware

The MAXREFDES27 IO-Link optical proximity sensor consumes minimal power, space, and cost, making it an all-around solution for many industrial control and automation proximity sensing applications.

The MAX14821 IO-Link device transceiver is IO-Link version 1.1/1.0 physical layer compliant with configurable outputs (push-pull, pnp, or npn), reverse-polarity/short-circuit protection, extensive fault monitoring all in a tiny 2.5mm x 2.5mm WLP package.

The MAX17552 high-voltage synchronous step-down converter efficiently converts 24V to 5V with an ultra-small footprint. The MAX8532 then regulates the 5V down to 2.85V.

The MAX44000's integrated LED driver shines IR, then reads the IR reflected from the target object using its internal IR receiver with an I2C interface. The IR LED current is software adjustable and the MAX44000 is available in a miniature optical 2mm x 2mm OTDFN package.

For documentation purposed, the sub-board, which lies perpendicular to the main board and contains the MAX44000, is called MAXREFDES28.

An ultra-low-power RL78/G1A microcontroller with current consumption down to 66µA/MHz provides system control. It features 64kB on-chip programmable flash memory, 4kB on-chip data flash, and operates down to 1.8V, all in a tiny 3mm x 3mm LGA package.

Transient voltage suppressor (TVS) diodes are not all equal. The SDC36 TVS diodes have a clamping voltage less than 55V and meet both IEC 61000-4-2 (ESD) and IEC 61000-4-4 (EFT). There are many smaller TVS diodes on the market that cannot meet these specifications.

Care must be taken when selecting resistors in a 24V (18V to 30V) system. Though designers may need the smallest size components, avoid using resistors in 0201 case sizes if they connect to 24V during normal operation. Resistors can fail by exceeding their maximum working voltage even if their maximum power rating is not exceeded.

The MAXREFDES27 uses an industry standard M12 connector allowing a 4-wire, or the conventional 3-wire, cable to be used, keeping costs low. The MAXREFDES27# consumes less than 7mA (typ).

Detailed Description of Software

The MAXREFDES27 was verified using TMG TE's TMG IO-Link Device Tool V3, which comes with the purchase of the TMG-USB IO-Link master TS hardware. Contact TMG TE for more information. It was also verified using Balluff's IO-Link Device Tool version 2.11.1, which comes with the purchase of the Balluff USB IO-Link master, part number BNI USB-901-000-A501 (see Figure 2). Contact Balluff or one of their local distributors for ordering information. Figure 3 shows a screen shot of the Balluff IO-Link Device Tool.

Detailed Description of Firmware

The MAXREFDES27 ships pre-programmed as a working IO-Link proximity sensor ready to connect to an IO-Link master. The firmware targets a Renesas RL78 microcontroller and follows the simple flow chart shown in Figure 4. The firmware is written in C using the IAR embedded workbench from IAR Systems and utilizes TMG TE's IO-Link device stack.

After hot plug-in, the MAXREFDES27 waits for a wake-up signal from the IO-Link master. After receiving the wake-up signal, the MAXREFDES27 synchronizes to the IO-Link master's 230.4kbps baud rate (COM3). Communication parameters are exchanged. The MAXREFDES27 then starts a cyclic data exchange every 2ms by sending the sensor process data to the IO-Link master. If the sensor is removed, the IO-Link master will detect a missing sensor.

Detailed Description of Use Cases

There are two different use cases that you should consider before purchasing MAXREFDES27. Use case 1 is simply using the MAXREFDES27, which is pre-programmed to connect with a user-supplied IO-Link master and IO-Link cable as shown in Figure 5. Use case 2 is where the entire firmware development system is needed as shown in Figure 6.

Source code is only provided with use case 2, which is the Renesas Starter Kit for RL78/G1A. Contact Renesas Electronics for more information.

Quick Start (Use Case 1)

Required Equipment:

• Purchased from Maxim: MAXREFDES27 board
• User supplied:


• Windows^® PC with a USB port
• Balluff USB IO-Link master, part number BNI USB-901-000-A501
• Balluff IO-Link Device Tool (tested with version 2.11.1 and comes with IO-Link master)
• M12 4-pin or 3-pin IO-Link cable (BCC05MC)

Note: Verify with Balluff that your version of Windows is supported before purchasing their software.

Equipment Used:

• Metric ruler
• Windows 7 PC with USB port
• MAXREFDES27 board
• Programming adapter (MAXREFDES23DB) board
• Balluff USB IO-Link master, part number BNI USB-901-000-A501
• Balluff IO-Link Device Tool (tested with version 2.11.1 and comes with IO-Link master)
• M12 4-pin or 3-pin IO-Link cable
• RD27_RL78_VXX_XX.ZIP (IODD file); where XX_XX = latest version from webpage

Special care must be taken and the proper equipment must be used when testing the MAXREFDES27 design. The key to testing any high-accuracy design is to use sources and measurement equipment that are higher accuracy than the design under test. These measurements were taken at room temperature without a sensor enclosure lens and also without a sensor enclosure. Figure 7 shows typical ADC codes collected for changing object distance and changing IR LED current (IOUT) for a white box object. Figure 8 shows typical ADC codes collected for changing object distance and changing object type (white cardboard box, aluminum box with matte finish, and black cardboard box). Figure 9 shows the typical total sensor current for changing values of IR LED current, which shows that the total power used by the sensor is only minimally affected by the IR LED current.

References

• Machine Design article: "Proximity sensors compared: Inductive, capacitive, photoelectric, and ultrasonic.”, Photoelectric sensors section.
• IO-Link System Description 2013 by IO-Link Company Community. Page 3, Preface.

_{IO-Link is a registered trademark of ifm electronic GmbH.}

_{Renesas is a registered trademark and registered service mark of Renesas Electronics Corp.}

_{Windows is a registered trademark and registered service mark of Microsoft Corp.}