Modern cars feature numerous advanced driver assistance systems (ADAS). All safety-critical ADAS applications must be designed for high availability. Automated driving functions are even more challenging to implement as these introduce fail operational requirements and the so called “dependable electronics” which enable systems that are the foundation for trust. More details, you can find on the Infineon “dependable electronics” pages.
The impact of these application requirements on the primary power distribution is the introduction of safety elements to guaranty a fast failure isolation in less than 100 … 500 µs. As fuses can’t fulfil this requirement, a partial or full electrification of the primary power distribution is the consequence. The electrical part of the primary power distribution is no longer called a Pre-Fuse Box, but primary Power Distribution Center (primary PDC).
The primary PDC is a functional block with supply, control, communication and sense & actuation functions. Infineon provides a complete chipset solution for the primary PDC to simplify design-in with scalable product families.
Today, one of the major challenges facing designers is the need of wire harness optimization to reduce its significant cost, length, weight and complexity. A possible solution is the transformation of the power distribution system from a centralized to a decentralized architecture.
In a first step, the central relay & fuse box may split into front, left, right and rear. But the location is restricted to easily accessible areas to limit labor cost in case of relay or fuse malfunction. To enable higher reliability, diagnose capability, protection features and smaller size, the secondary power distribution is getting partly or fully electrified. The electrical part of the secondary power distribution is no longer called relay & fuse box, but secondary Power Distribution Centers (secondary PDCs), which can get located anywhere in the vehicle, even in non-accessible areas.
Each secondary PDC is a functional block with supply, control, communication and sense & actuation functions. Infineon provides a complete chipset solution for the primary PDC to simplify design-in with scalable product families.
Freedom from Interference due to fast failure isolation
Far-reaching driver assistance systems, “X-by-wire” systems and automated driving result in new functional safety requirements for developers. According to ISO 26262:2018, this also includes the provision of a high availability power supply for the driver assistance systems by the power distribution system (PDS). Equally important is the freedom from interference of other components and systems to the power distribution system, which can be achieved by introducing safety elements that isolate failures in less than 100 µs to 500 µs. Implementing semiconductor solutions enables us to achieve these goals which can’t get met by fuses.
Find out more about "Semiconductors in a high availability power distribution system"
In this 60 minutes webinar, you will learn and understand about:
- Automotive megatrends and the requirement for dependable electronics
- The concept of ASIL decomposition, ensuring high availability and freedom from interference
- Why semiconductors are the only solution for safety elements in high availability systems
- Chip-set solutions for the electronic Power Distribution Center (PDC) in such systems
- Outlook on what may come next to the Power Distribution System (PDS)
The highly available power distribution system
Today's systems are usually designed to be fail-passive. This means that in the event of a fault, the individual system goes to a safe state without power and is isolated from the overall system. In this way, negative interference effects on the overall system are avoided. But the driver must be able to take control immediately as a fallback level and, depending on the type of malfunction, bring the vehicle to a safe state. For this, the driver needs mechanical access to the system, which is no longer possible with X-by-wire systems and automated vehicles. Therefore, in these cases, all systems must be highly available – we also speak of fail-active or fail-operational – to independently bring the vehicle to a safe state within a certain time. This way, highly available systems not only avoid or mitigate potential cases of failure, but also allow safe, automated driving under all conditions.
The figure above shows a schematic and exemplary decomposed 12 V PDS consisting of a QM domain and two available, sufficiently independent power distribution channels (PD channel) in ASIL B(D). The three PD channels are color-coded according to their ASIL assignment. The safety-relevant functions, which must be highly available, are designed with corresponding redundancy and are each supplied from the available PD channel. These are shown with the color code “Available”. At the same time, the safety-related functions can be the source of an overvoltage or undervoltage in the PDS. None of these failure sources may have an effect on the PDS and the interference must be prevented with ASIL B integrity in accordance with the availability requirement for the PD channel. The freedom from interference must be ensured and is shown accordingly with the color code “freedom from interference”.
Implementation in the electronic power distribution center
The figure below shows a representative block diagram of an electronic power distribution center in the high availability power distribution system. Electronic power distribution center not only replace the classic pre-fuse box, relays, and fuse boxes, but also include the safety elements that enable the freedom from interference. They have the classic structure of an electronic control unit with a power supply, a microcontroller, a communication interface, and either a gate driver+ MOSFET or a high-side switch as safety elements. For implementing the electric power distribution center, Infineon's complete chip set solutions can be used.
