CAN Newsletter magazine
Infineon offers a chipset for upcoming EPS generations that includes semiconductor components such as power supply, micro-controllers, half-bridge drivers, Mosfets, CAN transceivers, and sensors.
This article originally appeared in the March issue of the CAN Newsletter magazine 2019. This is just an excerpt.
Electric power steering (EPS) has almost completely replaced hydraulic and electro-hydraulic systems. The advantages are obvious: They include higher energy efficiency, as there is no need for a constantly working, belt-driven pump. In addition, eliminating the hydraulic components simplifies manufacturing and maintenance. However, a reliable and efficient electric power steering system requires fine-tuned solutions based on powerful semiconductors. Infineon offers a chipset for upcoming EPS generations that includes all major semiconductor components such as power supply, microcontrollers, half-bridge drivers, Mosfets, CAN transceivers, and sensors. All of these components are already available. From a single supplier, customers receive everything included in a fine-tuned chipset, which will help to reduce development time and thus costs.
Electric power steering uses an electrically controlled motor as steering assistance. Sensors detect the steering torque triggered by the driver and forward the information to an electronic control unit (ECU), which then calculates the steering assistance required and controls the servomotor. Why supply an entire EPS chipset? The goal was to provide all the necessary semiconductor components for an electric power steering system and fine-tune them in a way that leads to a high level of availability and enables fail-operational or fail-safe operation. Correspondingly, coordinated components offer reliable interoperability and integrated compatibility. An important aspect was to guarantee functional safety - for this, all the relevant components not only have to meet the highest automotive quality standards, but also have to be designed according to ISO 26262.
Infineon has developed a demo board with chipset components and a mechanical demonstrator. The demo board controls a 6-phase electric motor. Figure 1 shows the demonstrator set-up and Figure 2 the demo board with all the chipset components. They include the power supply chips (Optireg PMIC, TLF35584), 3-phase half-bridge drivers (TLE9183QK), 32-bit micro-controllers (TC23x with 200 MHz and 2 MB Flash), torque sensors (TLE4998C8D), motor position sensors (TLE5309D) and angle sensors (TLE5014D), Mosfets (in the SS08 package), and the CAN FD transceivers (TLE9251VLE, TLE9252VLC).
All components used are well matched and designed for high functional safety, energy efficiency, and integration density. For example, the safety power supply is predestined for EPS systems and offers corresponding monitoring and protection functions for Asil (automotive safety integrity level ) D functionality, which is also supported by the bridge driver. All sensors are designed for systems according to ISO 26262 and offer very high measuring accuracy. The powerful micro-controller from the Aurix family can be selected for performance, flash capacity, timer architecture, and peripherals. In addition, the MCU has an integrated safety/security concept with ISO 26262 support, hardware redundancy and hardware security (HSM module).
Finally, the Mosfets offer very low on-resistance (RDS (ON) of 0,9 mΩ at 40 V) and excellent switching performance in rugged packages (SS08 or sTOLL). The demonstrator architecture is a 6-phase system with two independent, isolated 3-phase subsystems for the required redundancy (Figure 3). Therefore, the dual sensors, power supply chips, micro-controllers, half-bridge drivers, and Mosfet half bridges can be powered by two independent batteries for a fail-operational system. Both subsystems run independently of each other. Each of them contributes half the torque to the entire EPS system. In the case of a fault and thus a failure of one subsystem, the other would take over the EPS functionality on a proportionate basis.
In order to ensure high functional safety in cars, a system partitioning with redundancy and efficient, reliable sensors are required. This is the only way to ensure a high level of availability, thereby enabling the system to remain fully functional in the event of a component failure. Therefore, sensors in electric power steering systems must not only be very precise, but also ensure functional safety. The sensors used here can be applied in ISO 26262 systems. Infineon's answer to the demand for sensor redundancy is integrating two sensors in a dual-sensor package (Figure 4). The linear Hall sensor TLE4998C8D ensures accurate detection of the torque or steering moment.
It very precisely scans the linear or angular position and digitally compensates temperature and mechanical stress, which ensures excellent stability over the entire temperature range and lifetime. The TLE4998C8D integrates two independently programmable linear Hall sensor ICs with SPC (Short PWM Code) protocol. The protocol allows the measured data to be transmitted initiated by the control unit. For flexible use, customers can choose between different interfaces (Sent, SPC, PWM only as single-chip). The TLE5014D angle sensor is also a dual-chip version. This allows easy implementation of the required redundancy in system design. The sensor works extremely precise over the entire temperature profile and lifetime, making it ideal for use in power steering applications.
The sensors are preconfigured with respect to the settings and precalibrated with respect to the temperature. As a result, customers can easily implement them. Again, customers can choose between different interfaces (Sent, SPC, SPI and PWM). The dual-sensor chip TLE5309D combines an AMR and a GMR sensor with diagnostic functions in one package. The dual GMR/AMR angle sensors are used for analog angular position detection in safety-critical motor applications. The TLE5309D combines the very high accuracy of the AMR sensor with the wide measuring range of 360 degrees of the GMR sensor. Thanks to a short propagation delay (less than 9 μs) the sensor is prepared to meet highest requirements regarding speed and accuracy in electric motors and electric power steering systems. In addition, the sensor also offers a quick start of less than 70 μs and a low total power consumption.
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