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

Graphene Graphene has emerged as a key material for Hall effect sensors. New process technology allows a layer of carbon one atom thick to be placed using a modified chemical vapour deposition (CVD) process that is very similar to that used for making silicon chips. These devices have higher sensitivity than the silicon versions, but in the past were built by hand in research labs. plates, with versions for rotary and linear use, and with analogue or pulse width modulation (PWM) output or with Single Edge Nibble Transmission (SENT) outputs. The SENT protocol is defined by the SAE J2716 Rev 4 standard. Sensors can support various SENT data frame formats (H.2 and H.4) as well as error signal transmission on fast and slow channels. Several programmable output signal clamping levels extend the error-signalling capabilities to indicate various fault conditions, such as under/overvoltage, under/overflow of the signal path, and overcurrent. The signal processing includes magnetic field range, sensitivity, offset, and temperature coefficients, and are programmable in non-volatile memory. A one-pin programming interface enables simultaneous programming of several sensors via the output pins with a customised output from a magnetic input signal, and provides 10-bit output resolution supporting a maximum bandwidth of 5 kHz. Other devices support linear or rotary measurements that are immune to stray fields with either analogue, PWM or SENT outputs. For safety- critical ASIL B applications there are versions with dual dies to provide redundancy. Using a commercial process opens up volume production of the devices. The sensor itself is a single plate of graphene with four terminals – two to provide the bias voltage and two to pick up the field induced by the magnetic field. These need a separate box for the signal conversion and processing, as different applications require different bias voltages. Eventually these electronics will be integrated into a companion ASIC device for particular applications. The higher accuracy comes from the control over the number of carriers in the graphene, which can be tweaked by the CVD process. The single layer of atoms avoids spurious signals in the sensor. Off-the- shelf silicon sensors have a depth that may be only a few microns, but that can create an error from movement. This error can show up as an offset on the output sine wave from the sensor. The graphene Hall effect sensors have been tested with the high- power magnets at the CERN particle accelerator in Europe. Rotating the sensor through 360º showed Focus | Hall effect and magnetic sensors Some suppliers of Hall effect andmagnetic sensors Belgium Magcam +32 16 79 53 22 www.magcam.com Melexis +32 5722 6131 www.melexis.com Germany TDK Micronas +49 761 517 0 www.micronas.tdk.com Japan ABLIC +81 3 6758 6815 www.ablic.com UK Paragraf +44 1223 739782 www.paragraf.com USA Allegro Microsystems +1 508 854 5800 www.allegromicro.com Monolithic Power +1 425 296 9956 www.monolithicpower.com Honeywell +1 800 537 6945 www.honeywell.com Diodes Inc +1 972 987 3900 www.diodes.com API Technologies +1 508 251 6479 www.apitech.com Wafer probe testing of a graphene Hall sensor with an atomic force microscope (Courtesy of Paragraf) 36 Autumn 2022 | E-Mobility Engineering