10 High-speed voltage regulators are key to the safety of autonomous vehicles, writes Nick Flaherty. As autonomous driving systems advance, ensuring functional safety is critical. However, as operational conditions expand and vehicles assume more responsibilities, creating entirely error-free, malfunction-proof systems becomes increasingly challenging. In the case of electric power steering (EPS) or steer-by-wire failure during autonomous operation, there is a risk of losing vehicle control and a greater likelihood of lane departure. To mitigate this, the system switches to a subsystem that provides minimal steering assistance before transitioning to manual operation. However, even after control is transferred to the driver, the loss of power assistance significantly impairs operability, making it vital to have robust, fail-safe mechanisms in place. Similarly, any failure of the battery management system (BMS) can necessitate an emergency stop, potentially causing high-speed collisions, especially with following vehicles. A multi-tiered approach is essential to address the challenges of functional vehicle systems can have more time for appropriate fault handling, allowing for the implementation of more sophisticated safety mechanisms. Analogue voltage-monitoring integrated circuits can operate up to 20 times faster than digital devices, directly contributing to the safety-critical ability to meet FTTI requirements in vehicles, allowing more time in fault handling, and enabling complex safety mechanisms and new handling methods. For example, the S-19990/9 series of automotive step-up switching-regulator controllers can be used for backup power for electronic control units (ECUs). While most ECUs operate using 12 V auxiliary batteries as their main power supply, if a vehicle is subject to a severe impact, such as from a traffic accident or collision, and power is lost, the ECUs will stop operating. Backup power supplies can be installed for ECUs in electric door latches and E-Call communications to maintain operation for a set period of time, for example, even after an accident. This power is generally composed of capacitors/ batteries and a step-up circuit, because when low-voltage capacitors/batteries are used, a step-up circuit is required to boost this to 12 V of backup power. Safety Layered approach and backup power supply essential safety in autonomous vehicles. This strategy emphasises the importance of systems transitioning to a safe state when encountering unexpected situations. For example, the EPS should switch to a subsystem, providing minimal steering assistance through a safety mechanism before transitioning to manual operation. Similarly, the BMS should have a backup power supply to maintain critical functionalities. This layered approach provides redundancy, ensuring multiple safety mechanisms are in place to prevent or mitigate potential accidents. Transitioning to a safe state is a crucial process and involves three key steps: detection, notification and handling. The time to complete these steps is critical and that is regulated by the Fault Tolerant Time Interval (FTTI), specified in ISO 26262. Detection involves identifying anomalies in the system, and notification is the process of communicating this to the parts of the system responsible for managing faults. Handling is the final step, where the system takes action to mitigate the issue. This could involve activating backup systems, adjusting operational parameters or initiating a safe shutdown. By optimising these steps, particularly detection and notification, autonomous Functional safety timing (Image courtesy of Ablic) December/January 2025 | Uncrewed Systems Technology Functional safety timing (Image courtesy of Ablic)
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