With unmatched precision and speed, how are TMR sensors set to transform current sensing and drive the future of automation and EVs? Ram Santhappan of Allegro MicroSystems explains their innovations to EFY’s Nidhi Agarwal.
Vice President, Global Marketing and Applications, Allegro MicroSystems
Q. How are TMR sensors different from traditional current sensors?
A. Our sensors are based on XtremeSense Tunnelling Magnetoresistance (TMR) technology, which identifies the magnetic fields generated by current flowing in a circuit. By avoiding the energy loss of traditional sensors that use shunt resistors to measure current, TMR sensors offer faster response times, higher efficiency, and better accuracy by detecting minute magnetic-field changes. They also exhibit minimal hysteresis, ensuring consistent, repeatable measurements.
Q. How are they better than Hall sensors?
A. You see, the TMR sensors have a better signal-to-noise ratio (SNR), making them more precise and sensitive for detection. The technology also responds faster, with less delay, which is crucial for protecting expensive electronics using gallium nitride (GaN) and silicon carbide (SiC) field-effect transistors (FETs) that require rapid response to current changes. While Hall sensors can support up to 5MHz bandwidth, TMR sensors can operate effectively at higher frequencies.
Q. How are they suitable for GaN and silicon carbide devices?
A. TMR sensors are essential in safeguarding delicate components of GaN and SiC devices with better SNR, as wide band gap switches demand rapid current measurements to avoid catastrophic damage. If the circuit draws too much current and there is a delay in response, the switches can be permanently damaged. Enter TMR sensors—high-speed, precision devices that quickly detect and respond to current fluctuations, ensuring switches remain safe and operational.
Q. What are the potential applications of TMR sensors?
A. Our new sensor measures up to 1000 amps of current directly on a circuit board without the need for a magnetic core. Compact and sleek, it fits effortlessly onto the board, enabling applications across power supplies, medical devices, aerospace, and industrial systems. The main users include data centres that are essential to artificial intelligence (AI). By swiftly detecting overcurrent situations it can shut down equipment before any damage occurs, protecting valuable machinery, whether in motors, robotics, or any high-current environments.
Q. What hurdles do you encounter while designing?
A. To save space, we aim to make the chips as small as possible. But every innovation has its own set of obstacles. One of the major challenges we face is managing the internal lead frame, as the current flows through it due to the integrated current sensor. To ensure the sensor is sensitive enough for accurate detection, extensive testing and simulations are required. Additionally, with millions of sensors, each must consistently meet a specific error range. The manufacturing process is complex and requires strict standards for materials.
Q. What are the trade-offs in designing?
A. It depends on the product’s environment. One can assess the noise level and available space to decide between a bus bar or routing on a circuit board. If space is tight, you can opt for a smaller design. It is the surface-mount packaging that makes our product better, eliminating the need for an external current sensor module.
Q. How is making TMR sensors different from manufacturing Hall sensors?
A. As I mentioned, TMR sensors offer better SNR and faster response than Hall sensors but the manufacturing of TMR sensors is also more complex in comparison. In addition to the digital and analogue signal processing circuits fabricated using the complementary metal-oxide semiconductor process, a specialised TMR material layer is deposited on top of the silicon wafer. This additional step, which is not required for Hall sensors, necessitates tailored equipment and increases production costs. The TMR layer is critical for creating smaller, higher-impedance sensors, thereby improving their signal-to-noise ratio.
Q. What technical challenges do integrated current sensors encounter?
A. Integrated current sensors generally work well but can be affected by electromagnetic interference (EMI). High-power applications need specialised designs to manage EMI. Achieving high accuracy and precision in current measurements is challenging due to temperature variations, noise, and offset errors. Measuring very high currents requires a bus bar, which poses its own challenges.
Q. How do you deal with electrical noise?
A. Proper printed circuit board (PCB) design guidelines are provided to ensure optimised current measurement. When using bus bars, it is recommended to cut shapes such as S and U into the bus bars. This increases current density, resulting in stronger magnetic fields that can be measured more accurately. Sometimes, sensors are placed on either side of the notches to cancel common-mode noise and stray-field interference.
Q. What testing methods do you use to ensure your product functions correctly before release?
A. We check our designs in multiple ways during the design phase to make sure they work as expected. There are simulations in the early design phases, followed by verification and validation tests before it goes into manufacturing. Once the integrated circuit returns from manufacturing, bench and automated tests are conducted to validate all features and specifications.
Q. How do you evaluate and improve the performance of your products over time?
A. Continuous improvement is essential as market demands evolve and customers use our products in new ways, presenting new challenges—such as increased sensitivity requirements. For instance, while a 1 per cent total measurement error was once acceptable, customers now expect 0.5 per cent accuracy. We conduct ongoing experiments to assess potential improvements and keep customers informed about achievable advancements, driving innovation in new product development.
Q. Does the environment affect your products?
A. Yes, we test our products in different environments to make sure they meet quality standards. We verify that they can operate at temperatures from -40 to 150 degrees Celsius, as required by Automotive Electronics Council Q100 Grade 0. Maintaining this level of quality over many years has always been a challenge, and Allegro has striven to do so.
Q. What is your company doing to keep improving its products?
A. The most important thing we do is keep innovating. Our chief technology officer’s office is constantly exploring what needs to evolve, improve, or be reimagined to stay ahead of the curve. While I may not have specific examples to share at the moment, our research and development efforts never stop. We are relentlessly focused on enhancing performance, minimising power consumption, and, as I said earlier, reducing product size because, as technology advances, the demand for smaller, lighter, and more energy-efficient solutions continues to grow.
Q. How do you help take care of the environment?
A. We prioritise automation and energy efficiency, which helps reduce environmental impact. We use less energy and operate more efficiently. Beyond improving our own energy use and recycling, we create products that help our customers to make their own designs more energy-efficient.
Q. What is your role in the automation industry and electric vehicle market?
A. In markets like electric vehicles (EVs), clean energy, cloud computing, and automation, the focus is on energy efficiency and automation. Our products, including current sensors, gate driver ICs, and position sensors, are designed to enable energy conversion and precise control. For example, in factories, robotic arms rely on sensors and motor drivers to achieve accurate movement. Similarly, in cars, our sensors and drivers are used in power steering systems. Additionally, our power management ICs enable efficient, safe voltage conversion, a critical function in EVs and other energy-conscious applications. As industries push for smarter, more efficient systems, our technology helps drive the future of automation and energy optimisation.
Q. Do you have plans to begin manufacturing in India?
A. Right now, we do not have any facilities or partners in India for manufacturing, but we have engineering and sales offices in India. This status may change as India continues to develop. As a fabless company, we design our products and have them manufactured by our fab partners in the United States, Taiwan, and Southeast Asia. We plan to start manufacturing in China soon.
