Why Automotive is Choosing TMR Sensors

automotive sensors

The demand for EVs is outpacing even the most aggressive predictions. According to Bloomberg, by 2025, more than half of all new car sales will be electric. With this demand comes the requirement for high- precision measurement to ensure a long-life drive battery and a precise control system for charging and discharging. In the all-critical measurement of range, battery capacity, state-of-charge, and energy consumption all must be accurately calculated.

Historically, companies manufactured pieces of copper that acted as resistors to measure current via Ohm’s law. Soon, these “Shunts” expanded beyond copper to a number of alloys, primarily manganin, due to its low temperature drift. Soon, they developed precision Shunts, which were laser trimmed for an exact resistance value. To further optimize, Shunts became “smart,” so that companies could read the shunt’s signal and provide their customers with a solution that reads current and outputs in both analog or digital. Smart shunts became more versatile and reliable incorporating additional features, such as isolation, calibration, and signal conditioning.

In addition, to Shunts, Hall-effect sensors were used for high current measurement. The choice depended solely on whether the application needed accuracy or bandwidth. Accuracy, in a Battery Management Unit for example, required Shunts, while bandwidth, say in a traction inverter, required Hall.

Of course, it is possible to make Hall as accurate as shunt, but at a prohibitive cost. Which is why shunt module makers, are primarily focused on BMS applications in EVs. However, these shunt makers still employ Hall for redundancy (using both to achieve ASIL-D safety rating targets) and for low cost (in smaller mobility vehicles like bikes and ATVs.)

But today, manufacturers are replacing Hall with superior-performing Tunnel Magneto Resistance (TMR) sensors, which feature 10x lower noise than Hall. TMR is used in the Battery Management Unit as a redundant current sensor to the shunt or as the primary sensor for smaller electric vehicles.

In fact, recently, a leading parts manufacturer launched a new lineup of electric vehicle products based on a magnetic sensor built around an integrated sensor from Crocus Technology. Crocus Technology’s TMR XtremeSenseTM sensor achieves high accuracy of 1.0%FS or less over the entire temperature range and low power consumption of 6mA or less, making it more efficient than conventional products.

Crocus’ TMR XtremeSense sensor provides a host of improvements, including more accurate measurement, higher sampling rate, lower temperature drift, lower power consumption, better thermal stability, better resolution, high signal to noise ratio, better linearity and higher sensitivity. The sensor measures current by reading the magnetic field generated in power distribution systems using integrated TMR magnetic sensors, ensuring highly accurate and versatile sensing solutions that differ from conventional Shunt products.

Shunt Module Challenges

As accuracy requirements continue to increase, traditional Shunt modules are challenged to remain cost effective, as total solution costs increase dramatically. Shunt designers are routinely faced with a balancing act to select the correct combination of resistor, operational amplifier, and implementation topology. Designing an accurate and cost-effective shunt based current sensing solution requires a substantial engineering effort.

In addition, with Shunt resistors, you still are faced with a trade-off of precision and dissipated power, and you’ll experience voltage drops that may not be acceptable for low voltage, high current applications. Users are also frustrated with Shunt’s weaknesses in thermal dissipation, size, isolation, system complexity and high cost.

Finally, another concern with traditional shunt solutions is the supply chain, where a complicated architecture like Shunt incurs additional risk. Simply put, more parts = more things to go wrong = more reliance on the supply chain = more risk. Crocus XtremeSense’s reduced component count and simpler supply chain response delivers a safer solution.

The TMR Advantage

These new TMR sensors enable a no-compromise design solution by combining high bandwidth response and high accuracy. This technology detects extremely small variations in AC or DC currents while achieving an unprecedented total output error of less than 0.7%. The coreless sensors are not only smaller in size than Shunt, but they also provide 99% immunity to stray magnetic fields, dramatically improving accuracy.

Crocus XtremeSense sensors are integrated with the busbar, eliminating the need for position adjustment between the sensor and busbar. This method implements busbar mounting for large current applications of TMR sensor ICs. With this busbar mounting, the sensor is directly mounted on the busbar, ensuring that it is always in the correct position.

Crocus XtremeSense sensors boast the highest level of precision among magnetic sensors and is a rare technology that only a few companies in the world can supply. Major car manufacturers have already adopted this chip, proving its quality and effectiveness, and Crocus was able to meet their stringent delivery times of 12 weeks.

Bottom line: Shunt makers made the jump from simple copper to integrated electronics. The next jump is to TMR. Crocus Technology’s powerful XtremeSense sensors are essential for the future of the automobile industry, as they deliver a more efficient and accurate way to detect current in EVs, automatic transporters, EV charging stations, solar power generation systems and motor control applications.


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