Allegro Microsystems has recently launched two new current sensors to improve magnetic sensitivity through tunnel magnetoresistance (TMR) technology.
The new sensors are the first offerings released since Allegro acquired Crocus Technologies. Image (modified) used courtesy of Allegro Microsystems
Industries such as automotive, renewable energy, and industrial automation rely heavily on accurate, current measurements to enhance performance, guarantee safety, and improve energy efficiency. However, traditional current sensing methods, like Hall-effect sensors and shunt resistors, often struggle with limitations in sensitivity, power consumption, and size. TMR technology, like that found in Allegro’s new CT455 and CT456 chips, is a promising alternative, offering high sensitivity and low power consumption in a compact form factor.
Allegro Introduces Two Current Sensors
Allegro’s CT455 and CT456 are high-bandwidth, low-noise, contactless current sensors built around Allegro’s patented XtremeSense TMR technology. Allegro designed both sensors to deliver precise current measurements and programmable features for enhanced flexibility across applications, including battery management systems, power inverters, and DC-DC converters.
The CT455 operates with a 1-MHz bandwidth and offers programmable gain for precise measurement. The device supports both 3.3-V and 5-V power supplies and comes in standard bipolar and unipolar magnetic field sensing variants. The sensor supports magnetic field ranges from ±6 mT to ±48 mT, offering a sensitivity of 333.3 mV/mT at lower ranges and 41.7 mV/mT at higher ranges. The device features a response time of less than 300 ns, a linear analog output, and low noise performance. It also only requires a supply current of 6 mA.
CT455 functional block diagram for SOIC-8. Image used courtesy of Allegro Microsystems
The CT456, on the other hand, offers an improved response time of 300 ns and shares the same 1 MHz bandwidth and 6 mA current consumption. Similar to the CT455, it provides a linear analog output and includes a programmable variant to fine-tune gain and offset at the end of production. The CT456’s architecture supports two preset magnetic field ranges (±6 mT and ±12 to ±48 mT) and also integrates advanced common-mode rejection, achieving over 90% immunity to stray magnetic fields. It operates with a supply voltage of 3.3 V or 5 V, with a voltage output range that spans from 0.5 V to 4.5 V for the 5-V variant and from 0.65 V to 2.65 V for the 3.3-V version. Allegro optimized the CT456 for automotive applications, with the device meeting AEC-Q100 Grade 1 standards.
What Is TMR Sensing?
TMR sensing is an advanced current sensing technology that uses quantum mechanical effects to detect magnetic fields precisely.
Central to TMR sensing is the magnetic tunnel junction (MTJ), a structure consisting of two ferromagnetic layers separated by an ultra-thin insulating barrier. The electrical resistance of an MTJ changes in response to external magnetic fields, making TMR sensors highly sensitive detectors for magnetic variations.
The principle of TMR. Image used courtesy of TDK
TMR sensors operate based on the tunneling magnetoresistance effect. When an external magnetic field influences a ferromagnetic layer’s relative magnetic orientation, it changes the probability of electron tunneling across the insulating barrier. If the magnetizations are aligned parallel, the tunneling probability is higher, resulting in lower resistance. If they are antiparallel, the tunneling probability decreases, leading to higher resistance. By monitoring these resistance changes, TMR sensors can detect minute magnetic field variations corresponding to the current flowing through a nearby conductor.
TMR sensors offer several advantages that make them a strong choice for current sensing applications. First, they exhibit exceptionally high sensitivity, detecting very small currents that might be missed by other sensor types. Second, TMR sensors have a high signal-to-noise ratio, which improves measurement accuracy. Third, they consume less power compared to traditional magnetic sensors like Hall-effect or anisotropic magnetoresistance (AMR) sensors. Finally, TMR sensors can be manufactured compactly, enabling integration into space-constrained electronic devices.
Available Now With Eval Boards
By leveraging TMR technology, Allegro hopes its new sensors will provide engineers with a long-sought-after combination of high sensitivity, low power consumption, and compact design. Samples of each chip are now available for purchase, along with evaluation boards.
