Led by demands of the electric vehicle market but extending widely to many other applications, magnetic current sensors are increasingly replacing sense resistors and current transformers. A few examples of new magnetic current sensing products illustrate the rapid-fire developments that are bringing change.
Semiconductor companies Allegro Microsystems and MultiDimension Technology (MDT) have both developed important new advancements in integrated circuitry lately but they are by no means alone as many product developers harness Hall Effect and tunnel magnetoresistance (TMR) technologies to address the opportunities for current sensing on different levels, fueling continued advancements and competition. This article highlights several new ICs from Allegro and MDT as well as new magnetic current sensor products and capabilities from others including Littelfuse, Vacuumschmelze and TDK.
Modern cars have become increasingly power hungry, points out Allegro. Even the least electrified vehicles include advanced electronics for infotainment, safety, and engine control. Fully electric vehicles further add high-voltage power domains to charge and drive. Each of these systems shares the need for power monitoring and control, and this is where current sensors are used.
Safety systems and powertrain electrification OEMs are implementing electrified steering and braking systems to increase vehicle safety and enable automated driving. These systems encompass one or more high-current motors to actuate the steering rack or brake caliper. Safety systems require current sensors to be small and have low heat generation.
A basic electric vehicle powertrain encompasses a charging system and a drive system. A charging system may experience 100A at 400V or 800V, while the drive system may need to deliver several hundred amperes of current to the traction drives. Current sensors require isolation and high current capability, while also operating from DC to a high bandwidth for efficient power conversion and system protection.
Current sensing needs have historically been met using sense resistors and current transformers, explains Allegro. The sense resistor (and associated shunt amplifier) provides V=I×R but suffers due to large size, high power dissipation, slow bandwidth, and no inherent isolation. The current transformer provides an isolated, high- speed measurement, but has drawbacks of large component height, no DC sensing, a narrow frequency band, and needing many external components to operate.
Magnetic current sensors are non-contacting sensor integrated circuits. This means the sensor silicon is not touching the conductor carrying the current. Isolation does not require extra components, and ranges from 100V to several thousand volts. The sensor measures the magnetic field generated by the current and outputs a voltage proportional to that magnetic field. Some magnetic current sensors are placed close to a current- carrying wire while others integrate a conductor path inside the component for ease of implementation.
A magnetic current sensor can provide significant advantages over sense resistors and current transformers in automotive power systems. Compared to a sense resistor, the magnetic current sensor offers a smaller size, lower power dissipation, and higher bandwidth with integrated isolation. Advantages of magnetic current sensors over current transformers are smaller size, DC measurement, and minimal external components.
New ICs from Allegro
In January, Allego launched two new current sensor ICs that leverage its sensing technology. Depicted at top, the ACS37030MY and the ACS37220MZ provide low internal conductor resistance, high operating bandwidth and reliable performance across a wide range of automotive, industrial and consumer applications.
“We’re excited to introduce our latest current sensor ICs, as Allegro continues to push the boundaries of sensor IC technology,” said Ram Sathappan, Vice President of Global Marketing and Applications. “Our newest sensors establish new standards for precision and reliability, empowering customers to overcome design and efficiency standards, while also demonstrating how our technology is driving a smarter, more efficient future.”
They are designed for precise current sensing in a compact and durable package. Featuring a widebody design, the ACS37030MY and ACS37220MZ deliver higher isolation in a 40% smaller footprint compared to the existing 16-pin packages on the market. The innovative new designs also incorporate lower resistance, which helps to reduce power dissipation.
The ACS37030MY is a fully integrated current sensor IC with fast response time for protection of wide bandgap GaN devices. It uses a combination of Hall-effect and inductive coil signal paths to sense current over a wide frequency range. The innovative package offering enables a product which is both 5x faster than existing solutions but also 40% smaller.
The ACS37220MZ fully-integrated, Hall-effect current sensor features a 150 kHz bandwidth and fault pin. This device is designed for value-line current sensing applications as a successor to the popular ACS724/5 family of products. The new package of the ACS37220MZ offers a 40% smaller solution size and lower resistance for lower power dissipation.
Additionally, Allegro has recently expanded its portfolio with new XtremeSense TMR sensors that use tunnel magnetoresistance technology to provide the high magnetic sensitivity, low power consumption and small size by comparison to other magnetic technologies such as Hall effect, anistropic magnetoresistance (AMR) and giant magnetoresistance (GMR). Accelerating various applications from renewable energy systems, xEV and connected consumer devices, the TMR technology enables current and position sensors to achieve industry-leading performance figures and cost levels, says Allegro.
A thin-film magneto-resistive device called a Magnetic Tunnel Junction is central to the technology. In its simplest form, the MTJ consists of two electric-conducting magnetic layers on either side of a thin but highly robust insulating layer. One magnetic layer has a fixed magnetic moment direction, while the other can change freely to follow the direction of the local magnetic field.
MultiDimension Technology, a leading manufacturer of magnetic sensors specializing in TMR technology, has recently added several current sensors to its extensive portfolio. As previously reported in Magnetics Magazine, the TMR7616-C series current sensor IC provides TMR performance in a compact SOPW16 form factor. It is highly sensitive, featuring a sophisticated design built upon electromagnetic induction principles. Its high signal-to-noise ratio ensures precise current measurements.
Littelfuse Launches Residual Current Monitors for EV Charging Stations
In October, Littelfuse introduced the RCMP20 Residual Current Monitor Series for Mode 2 and Mode 3 EV charging stations. The monitors set a new standard in charging safety, offering superior performance and flexibility in a compact design while supporting higher charging currents than other solutions on the market, says the company. Their large current transformer aperture expands the Littelfuse EV infrastructure portfolio and enhances electrical safety in EV charging applications.
Vacuumschmelze current sensors and alloys
In a specialized approach from Vacuumschmelze, integrating a VAC differential current sensor into an IC-CPD or wall box provides the EV charging electronics with all-current sensitivity and electrical safety at a low cost. If the sensor detects a fault current, the corresponding output will change its state. Design variants with integrated primary conductors for one- or three-phase systems are available, together with a pass-through variant.
TDK magnetic current sensors for EV charging
TDK, a prolific developer of magnetic sensing products, recently came out with the CUR 4000 sensor for current measurements in automotive and industrial applications such as high-voltage battery monitoring systems of hybrid and electric vehicles. A flexible multi-Hall array allows linear or differential magnetic-field sensing for contactless and precise current sensing up to ≥2000 A. It can be used for different module concepts like core-based or coreless. In linear modes, a configurable array of Hall elements enables highly accurate measurements for core-based stray-field robust sensor-module designs. The differential mode enables small coreless and stray-field robust system designs without shields.
For more info, see www.allegromicro.com, www.dowaytech.com, www.littelfuse.com, www.tdk.com, www.vacuumschmelze.com.
