E-Mobility Engineering 015 l EMotive Scarab off-road truck dossier l In Conversation: Giulio Ornella l Hall effect and magnetic sensors focus l Challenge of batteries for heavy-duty EVs l Alpha Motor Corporation digest l Automated charging insight l HVAC systems focus

Other Hall effect sensors used for rotational measurements for sensing speed might need higher sensitivity, as the magnetic fields being measured are much lower. Applications such as measuring low speeds when parking can require higher sensitivity. For the rotational sensors, a key consideration is communication with the digital controller. This can be a traditional two-pin, two-wire interface carrying an analogue signal to an ADC in the controller, although there is increasing demand for a one-wire connection. However, there are fewer controllers available with such an interface. Material such as GaAs and InP can also be used for GMR sensors that have multiple layers of materials rather than Hall plates. These can have greater sensitivity than the typical 1% of a Hall effect sensor. Resolution is critical for controlling the charging current steps in fast charging. Here, milliamp resolution is more than enough, as 1% resolution would be accurate to 1 A for a 100 A fast charger. Designers are also now looking at making the Hall effect work for cell balancing in the battery pack rather than using shunt current sensors. These do not yet meet the accuracy requirements of under a milliamp, as the currents flowing between cells can be around 10 A for lithium ion-cells, which is where GMR sensors are being evaluated. However, Hall effect sensors can be suitable for cell chemistries such as lithium iron phosphate, where the higher accuracy is not required. Sometimes Hall effect sensors are used to monitor the input to the pack; sometimes they are placed in selected areas in the pack. This becomes a challenge though, as the wires have to come out of the battery pack, which can leave the pack susceptible to electromagnetic interference. This requires very careful placing of the sensors within the pack. A range of devices is possible with different designs of Hall effect of the results. While the sensor itself is almost immune to the effects of electrical noise, taking the signal off- chip can increase the opportunity for noise to enter the system. Some Hall effect sensors use materials such as gallium arsenide (GaAs) or indium phosphide (InP), which are more expensive to process, to achieve more sensitivity as there are more carriers – that is, electrons available – compared to silicon. However, more processing can be integrated into the silicon devices to compensate for that, and the resolution of the signal is determined more by the operational amplifier and analogue- to-digital converter (ADC) for the signal conditioning than the intrinsic performance of the Hall sensor itself. While the sensor may be immune to noise, there are other factors that need to be considered and compensated for. The on-chip processing also includes temperature monitoring and compensation for vibration, in particular for EVs. It might also include redundant circuitry for safety-critical system designs. In some instances a magnet can be integrated into the chip package to provide a constant field for calibration. There are different ways to arrange the Hall effect plates, sometimes with a differential output to eliminate noise and the temperature cycling and vibration. The signal conditioning circuits can characterise the performance and bias the sensor, compensating for environmental conditions. This is essentially a sophisticated look-up table with the results of the bias current at different voltages and currents. There are also different resolution and sensitivity requirements for different applications. For example, a Hall effect device used for a current sensor on a busbar with hundreds of amps flowing through it only needs a sensitivity of milliamps. This can require less signal conditioning to provide a suitable signal-to-noise ratio. A precision, low-offset linear Hall circuit with a copper conduction path near the surface of the die. Applied current flowing through the path generates a magnetic field that the Hall IC converts into a proportional voltage (Courtesy of Allegro Microsystems) Autumn 2022 | E-Mobility Engineering 35 Focus | Hall effect and magnetic sensors