Magnet-free design achieves high environmental resistance: Features and comparison of various types of Renesas inductive position sensors (IPS)

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Position sensors play a crucial role in detecting the location of various devices, such as motor control, valve opening detection, and steering angle detection. However, in recent years, in addition to being required to withstand high-temperature and vibrating environments, there has also been a need to address the rising prices and supply risks of magnets that use rare earth elements.

Against this backdrop, inductive position sensors (IPS), which can detect position without contact and without using magnets, are attracting attention.This article explains the features of IPS through a comparison with representative position sensors and introduces the lineup of Renesas IPS.

Position sensor detection method

Position sensors can be broadly divided into two types based on their detection method, as shown in the diagram below: "contact type" and "non-contact type".

Contact-type sensors, exemplified by variable resistors, use mechanical contacts to detect the position of an object. While their structure is relatively simple and easy to handle, a challenge they face is that the physical sliding of the contacts during operation limits product life due to wear and aging.

In contrast, non-contact methods detect the position of an object without mechanical contact between the sensor and the object being detected. Optical, magnetic, resolver, and inductive methods are typical detection methods. Because there are no mechanical contacts, wear is less likely to occur, and it is easier to construct a long-lasting and reliable system.

In particular, for applications that require environmental resistance to magnetic fields, dust, and vibration while ensuring a certain level of detection accuracy, the inductive method is a promising option. A major advantage of the inductive method is that it can perform stable position detection without using magnets and without contact.

Comparison of the features and challenges of typical position sensors and IPS sensors

This article compares the features and challenges of various types of position sensors. IPS is a position detection method suitable for situations where detection accuracy is ensured while also requiring resistance to environmental factors such as magnetic fields, dust, and vibration.
In particular, given the price fluctuations and supply uncertainties of magnets and their raw materials, rare earth elements, the fact that IPS does not require magnets is a major advantage. Because it can detect position without magnets and without contact, it is a method that can easily achieve stable position detection even in harsh operating environments while reducing the risk of procuring magnets.

Position sensor types	Contact method	Features	Key challenges
Potentiometer	contact type	Low cost • Simple structure	- Deterioration due to aging and poor contact caused by contact
Optical encoder	Non-contact type	・High resolution, high precision • High-speed, low-latency signal response	- Dust and oil may affect the optical path. • High cost
Magnetic encoder		・Easy to downsize • Resistant to dust and vibration	• Magnetic field influence present
resolver		・High environmental resistance • Proven track record of long-term adoption in the automotive sector.	• Large size, high cost
IPS		• Magnet-less ・High environmental resistance	• Expertise is required for coil design.

Renesas IPS lineup

From here, we will introduce the Renesas IPS lineup, categorized by the features of each type of position sensor.

RAA2P4200/RAA2P4500 series

Supports contactless potentiometers

While potentiometers have the advantage of being low-cost and easy to implement, they have mechanical contacts, which means they are susceptible to wear and tear and deterioration over time. As an alternative to these contact-type issues, replacing them with IPS (Insulator Pressure Spectrometers), which do not use mechanical contacts, is attracting attention.
The RAA2P4200 (for industrial equipment) and RAA2P4500 (for automotive applications) feature a 12-bit analog output mode intended for potentiometer applications.
Because the output voltage continuously changes from the minimum potential to the power supply voltage depending on the position of the object being detected, it can be used in an output format similar to that of a conventional potentiometer.
A major feature of the RAA2P4200 and RAA2P4500 is that they maintain compatibility with potentiometer output while reducing wear and deterioration over time through non-contact operation.

Source: RAA2P4200 Datasheet Rev1.1
https://www.renesas.com/ja/document/dst/raa2p4200-datasheet

Reference source: RAA2P4200 Datasheet Rev1.1
https://www.renesas.com/ja/document/dst/raa2p4200-datasheet

RAA2P3200/RAA2P3500 series

Supports digital output encoders

The RAA2P3200 (for industrial equipment) and RAA2P3500 (for automotive applications) are digital output-enabled IPS chips that are less susceptible to noise and are suitable for connection to microcontrollers.
Because it employs an electromagnetic induction method that does not use magnets, it can suppress the mechanical design constraints and influences of external magnetic fields that are problematic in conventional magnetic encoders, which are caused by magnets.

The incremental output (ABI) supports high-speed response with propagation delays of 100 ns or less, making it suitable for feedback control where real-time performance is required.
Furthermore, because it features True Power functionality, even when using incremental output, the electrical absolute position, i.e., the current angle, can be obtained immediately after power-on.

Source: RAA2P3200 Datasheet Rev1.2
https://www.renesas.com/ja/document/dst/raa2p3200-datasheet

RAA2P3226 series

Supports high-precision encoders

The RAA2P3226 is an IPS (Instrument Sensor) that supports high-resolution position detection and absolute position acquisition. The sensing section employs a two-coil structure that generates signals with different periodic characteristics. By combining the signals obtained from each coil and utilizing the vernier effect, it achieves a high position resolution of up to 19 bits.

Furthermore, by using multiple phase signals obtained from two sets of coils, it is possible to calculate positional information that is unique to the machine angle, i.e., the absolute angle.
Therefore, it is possible to acquire the current position information immediately after power-on without performing the home position return operation required by conventional incremental encoders. The output interface includes UART and ABI, allowing for real-time output of high-resolution position information even in applications where the motor rotates at high speeds.

Reference source: RAA2P3226 Datasheet Rev1.2
https://www.renesas.com/ja/document/dst/raa2p3226-datasheet?r=25575164

IPS2550 series

Supports resolvers

The IPS2550 is an IPS designed for resolver applications, capable of directly outputting Sin/Cos analog signals similar to conventional resolvers. Because it features an output format similar to resolvers, it can be considered as a replacement while minimizing the impact on existing interface circuits and system configurations. Under ideal conditions, it supports position detection accuracy of ±0.1 % FS or less.

Furthermore, features such as Auto Gain Control (AGC) to compensate for variations in the air gap make it easier to ensure stable detection accuracy even in real-world usage environments.
Therefore, it is suitable for replacing resolvers and for motor position detection applications where high reliability is required.

Source: IPS2550 Datasheet Rev: April 24, 2024

https://www.renesas.com/ja/document/dst/ips2550-datasheet?r=1469886

RAA2P4520 series

Compatible with steering sensors

A key feature of the RAA2P4520 is its ability to configure a redundant position detection system on a single chip. Designed for steering applications, this IPS (Instrument Spot Detection) chip incorporates two independent receiving coils. This redundant configuration meets the functional safety requirements of steering systems, enabling system-level compliance with ISO 26262 ASIL D. Each output interface supports SENT (Single-Input Response), allowing for configurations tailored to the system requirements of the connected device.

Reference source: RAA2P4520 Datasheet Rev1.2

https://www.renesas.com/ja/document/dst/raa2p4520-datasheet?r=25577922

Summary

This article discusses representative position sensor detection methods, comparing their features and challenges, and introduces Renesas' IPS lineup, which is tailored to various applications. Position sensors, including contact and non-contact types, have different strengths in terms of applications and operating conditions. Among them, the inductive method is characterized by its ability to detect position non-contact without using magnets. It is a promising option when it is necessary to achieve both the required detection accuracy and environmental resistance in environments where the effects of magnetic fields, dust, and vibrations are a concern.

Furthermore, given the need to address price fluctuations and supply uncertainties of magnets and rare earth elements, the fact that it does not require magnets is a noteworthy feature from the perspective of reducing procurement risks. Renesas offers a wide range of IPS products that can be selected according to the required specifications, including potentiometers, digital output encoders, high-precision encoders, resolvers, and steering systems.