Characteristics and requirements of automotive MCUs

As a small chip tailored for performance, the MCU's performance indicators are a set of comprehensive indicators, including product core, main frequency, storage unit, external interface, control method, number of AD channels, operating voltage, packaging method, number of pins and temperature adaptability. When using it, users will also consider comprehensive factors such as the availability, cost-effectiveness and reliability of the tool chain. The MCU competition is based on the degree of understanding of application scenario requirements and a comprehensive package of indicators.

The downstream of MCU is embedded development. The principles of embedded development selection are: functional features, availability, cost and familiarity. MCU is an application-driven chip. The core is to serve customer needs and meet customer specifications.

Currently, automotive MCUs are mainly 8-bit and 32-bit products. Driven by the intelligence and electrification of automobiles, 32-bit MCUs have the largest increase and the fastest growth rate, and are also the automotive chip with the most serious shortage at present.

Due to the special working conditions of automotive MCUs, the working environment has high requirements for temperature and humidity, EMC, ESD, service life, and long-term supply capability. Compared with consumer electronics MCUs, consumer electronics MCUs pay more attention to PPA (power consumption, performance, area) and have a fast iteration speed. Automotive MCUs have high requirements for high reliability (quality, safety), large capacity (software iteration margin), and multiple interfaces (hardware must be upgradeable). Automotive MCUs need to adapt to the needs of OTA software upgrades in the next few years, leave enough space for on-chip resources, and have a deep enough understanding of the future iterations of automotive software.

Automotive chips have a low tolerance for chip failures, and the entire development concept of eliminating failures runs through the entire process. In the R&D and manufacturing stages, the chip design team is required to focus on prevention, and to detect and nip failures in the bud in advance through simulation verification. When the chip is already installed in the car, systematic and random failures must be eliminated, and sufficient redundancy measures must be taken to ensure the reliable operation of the chip. The design differences/design requirements between automotive chips and other types of chips are as follows:

There must be a dedicated development process closed loop: Automotive MCUs run a lot of industrial control, and reliability can be guaranteed according to different uses (such as body, chassis, power, ADAS, etc.). Reliability refers to the grading requirements of AEC-Q100, and functional software security relies on ISO 26262 requirements. The overall verification process must also meet functional safety requirements.

Consider redundant design: The automotive functional safety standard ISO26262-5 2018 product development requirements, as one of several measures to achieve high diagnostic coverage, hardware redundancy can include dual-core lock-step, asymmetric redundancy, and coded calculation. Common lock-step cores include Infineon's Tricore, and the M, R, and A lock-step cores provided by ARM (NXPS32G uses A core lock-step, and Nvidia Orin uses R core lock-step).

Automotive supply chain support is essential: wafer manufacturing production lines and packaging and testing production lines need to undergo third-party "production line certification" before mass production, and the certification cycle is 0.5-1 year. Once the production line is certified to produce automotive-grade products, in principle, the production equipment and process conditions cannot be changed. Once changed, re-certification is required. At the same time, due to the current large number of automotive MCU specifications, the process technology is mostly 40/45/65 nanometers, and the production line operating costs are high. Therefore, IDM factories such as NXP, Renesas, Infineon, Texas Instruments and Microchip Technology mostly adopt wafer outsourcing strategies, using the light wafer fab model (Fab-lite). 70% of the automotive-grade MCUs outsourced globally are mainly manufactured by TSMC, which makes it difficult for domestic start-up automotive-grade MCU manufacturers to obtain automotive-grade wafer manufacturing capacity support. After the release of automotive-grade MCUs, large-scale mass production has not been seen.