System Board 6218

MAXREFDES88#: Tiny Industrial Proximity Sensor Solution

Maxim Integrated’s MAXREFDES88# is one of the world’s smallest industrial proximity sensors featuring a complete binary magnetic proximity sensor. The device may be configured to PNP or NPN outputs and be configured as normally open or normally closed without any changes to the bill of material. LEDs indicate sensor open or closed and error detection. The sensor operates at the conventional industrial 24V, but also across a range of 7V to 34V. An integrated LDO provides 5V to other portions of the system. The entire system consumes roughly 30mW of power. This tiny sensor fits into just about any location and drastically extends your ability to sense in a control and automation application.

The board is designed in a compact form factor for rapid evaluation or installation. Refer to the


  • Ultra small
  • Pin-selectable PNP, NPN, or push-pull driver
  • Pin-configurable NO or NC logic
  • Integrated 5V LDO regulator and LED drivers
  • Integrated protection
  • Low power

Competitive Advantages

  • Flexible configurations
  • Ultra small
  • Low cost


  • Industry binary sensors
  • Proximity switches
  • Capacitive and inductive sensors
MAXREFDES88# System Board Enlarge+

MAXREFDES88# Reference Design Block Diagram Enlarge+


The MAXREFDES88# reference design is one of the world’s smallest proximity sensor solutions. The solution features one RedRock RR100 micro-electro-mechanical systems (MEMS)-based magnetic reed sensor and the MAX14838, an industrial sensor output driver. The MAX14838 integrates all of the high-voltage (24V) circuitry commonly found in industrial sensors, including a configurable PNP/NPN/push-pull driver and an integrated linear regulator that meets common sensor power requirements.

The MAX14838 is pin-configurable. Logic inputs allow the driver to be configured for high-side (PNP), low-side (NPN), or push-pull operation. An additional input allows the user to select between normally-open (NO) and normally-closed (NC) logic.

The MAX14838 also features an onboard 5V low-dropout (LDO) regulator and includes two LED drivers for visual feedback. One LED driver reflects the output logic status and the other is a general-purpose driver that can be used to signal a fault condition.

The digital output (DO), supply (VCC), and ground (GND) pins are reverse-polarity protected, and are protected against IEC ESD and surge events.

The MAX14838 operates from 7V to 34V and features a 5V LDO, whereas a similar part, MAX14839, operates from 4.75V to 34V and features a 3.3V LDO.

The reference design PC board dimension is approximately 26mm x 2mm and is assembled in a 26mm x 3mm hexagon aluminum enclosure for easy installation and variation of sensitivity, based on the angular sensitivity of the RR100.

MAXREFDES88# System Board Enlarge+

System Diagram

Figure 1. MAXREFDES88# reference design block diagram.

Detailed Description of Hardware

The MAXREFDES88# reference design system block diagram is shown in Figure 1. Also refer to the schematic for circuit details. The red wire connects to 24V power supply. The black wire connects to the ground. The yellow wire connects to the output.

The MAX14838 features an onboard 5V linear regulator, while the MAX14839 features a 3.3V linear regulator. Choose the appropriate drivers for specific sensor power level requirements.

The MAX14838 and MAX14839 are 24V, 100mA drivers for industrial binary sensors. These devices are pin-programmable and integrate the common high-voltage circuitry needed for industrial binary sensors into a single-device solution.

The MAX14838 and MAX14839 feature multiple configuration options that are user-selected during operation. The output of the device can be pin-configured for high-side (PNP), low-side (NPN), or push-pull operation. Additionally, the devices allow the user to configure the logic for sensors that are normally open (NO) or normally closed (NC). Refer the IC datasheet for configuration details. Use R2–R7 to implement all the possible configurations. By default, the MAXREFDES88# is configured for PNP and normally open operation. Because the MAX14838/14839 may be configured, sensor manufacturers may create a variety of sensor configurations, while stocking all of the same material.

The two integrated LED drivers in the MAX14838 and MAX14839 provide visual feedback of the state of the sensor.

These devices deliver the robust design necessary in industrial applications. Integrated transient protection meets the IEC 61000-4-5 standard and protects surges up to ±1kV/500Ω. The DO, VCC, and GND interface pins are protected against reverse-polarity connection, short circuits, and high ESD. These devices also feature fast inductive demagnetization of GND-connected and VCC-connected inductive loads up to 1.5H.

Overcurrent protection guards the MAX14838/MAX14839 from damage due to overheating during overcurrent fault conditions. The FAULT output signals thermal overload and overcurrents.

Quick Start

Required Equipment:

Purchased from Maxim:

  • MAXREFDES88# reference design

User supplied:

  • An adjustable 7V to 34V, 100mA power supply
  • A voltmeter

To verify the correct functioning of the MAXREFDES88#:

  1. Adjust the power supply output to 24V, disable the output.
  2. Connect the yellow wire and the black wire to the voltmeter.
  3. Connect the black wire to the power supply ground.
  4. Connect the red wire to the power supply positive output.
  5. Enable the power supply.
  6. Verify that the voltmeter should indicate a logic low output (approximate 0V), the yellow and red LED should be off.
  7. Use the provided magnetic bar to approach the RR100 sensor on the tip of the reference design, verify that the voltmeter should indicate a logic high (approximate 24V), the yellow LED should be on. The red LED should be off.

Lab Measurements

The MAXREFDES88# magnetic field spatial response was tested as shown in Figure 2. The objectives of testing were to determine the distance and direction in XYZ space where an NdFeB N52 cylinder magnet would cause the switch to close. The test magnet was 3/16” diameter, 3/8” long. The coordinate scheme is indicated in the picture. A microscope stage allows the magnet to be moved with a precision of 0.05mm in the X-Y plane, and a servo motor drives the magnet with a precision of 0.0010mm in the Z-axis.

Figure 2. MAXREFDES88# reference design magnetic field spatial response test setup.

Using the X, Y, and Z controls, the surface where the switch closed was mapped and plotted in a 3D graphics program. Figure 3 shows a stereo pair of the closure locus. The sensor is represented by the gray cylinder and the switch is shown in black. Both are in the same scale as the closure locus, which is shown as a red point cloud.

Figure 3. MAXREFDES88# reference design magnetic field spatial response.

RedRock is a registered trademark of Coto Technology, Inc.

Quick Start

Required Equipment:

Purchased from Maxim:

  • MAXREFDES88# reference design

User supplied:

  • An adjustable 7V to 34V, 100mA power supply
  • A voltmeter

All Design Files

Download All Design Files

Hardware Files


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Dual, 256-Tap, Volatile, Low-Voltage Linear Taper Digital Potentiometer

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2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or 28-Port I/O Expander

  • 400kbps I²C-Compatible Serial Interface
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  • -40°C to +125°C Temperature Range

Low-Voltage, 60Ω, 4:1 Analog Multiplexer in QFN

  • 3mm x 3mm 12-Pin QFN Package
  • Guaranteed On-Resistance:
  • Guaranteed Match Between Channels: 3Ω (max)
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