What is Automotive MCU and How to Choose 2022

Automotive mcu is a microcontroller used to control all electronic systems of a car, such as controlling multimedia, speakers, navigation and suspension.

1. What is Automotive MCU

The mcu is the core component of the automotive electrical control system and must have good high temperature performance and stability. Compared with the general mcu, the quality of the automotive mcu requires higher quality and is not easily damaged in the complex vehicle environment; according to the purpose of use, it can be divided into general purpose and special purpose. The hardware and instructions of the mcu are designed for specific purposes, such as the central recorder controller, voice broadcast controller, the motor controller, etc.; general-purpose automotive mcu can provide users with all available development resources, including ROM, RAM, I/O, EPROM, etc.

Features of automotive mcu

1. High processing performance

As the control brain of the car, it needs to carry various computing functions in the car system, such as the control system, multimedia, navigation system, etc., so it needs to have higher processing performance.

2. Excellent node processing capability

Automotive MCU connects various electronic systems inside the car, so in order to balance the coordination of various departments, it must have excellent node processing capability.

3. Strong reliability and stability 

Because of the safety of the driver's life, the stability and reliability of automotive MCUs are of paramount importance compared with ordinary electronic MCUs. Therefore, automotive MCU needs to undergo more stringent stability testing after production.

2. Classification of Automotive MCU

1. Categorization of automotive MCU according to the main purpose.

Dedicated: Its hardware configuration and commands are designed in accordance with certain types of special major uses and solutions, such as recorder core control board, copier control board, motor driver, etc.

2. Automotive MCU is categorized by the number of decimal digits of data information resolved during its operation.

Based on the total width of the system bus or data information staging, MCU design is further divided into 1-bit, 4-bit, 8-bit, 16-bit, 32-bit and even 64-bit automotive MCU design. 4-bit MCU is overwhelmingly used in computing methods, car with instrument panel, car with anti-theft equipment, call machine, wireless landline, CD player, LCD push control board, LCD arcade game machine, children's toys, weighing scales, charging head Tire pressure meter, temperature and humidity meter, controller and stupid camera, etc.;

8-bit MCU is mostly used in electric meter, motor controller, electric toy car machine, inverter type air conditioner, pager, printer, callerID, telephone recorder, CRT display, computer keyboard and USB, etc.; 8-bit and 16-bit MCU design is key to general manipulation industry, generally not The application of computer operating system, 16-bit MCU is mostly used in mobile phones.

In vehicle applications, microprocessors (automotive MCUs) are given particularly important characteristics. Along with the reduction of price and the improvement of solidification, MCUs are slowly becoming commercialized. However, for different automotive MCUs, there are still great differences, so it is increasingly important to choose the right automotive MCU to control the cost without jeopardizing the required features.

Microprocessors (automotive MCUs) are giving particularly important features in an increasingly wide range of vehicle applications from motor control systems to information content in-car multimedia and vehicle body handling. Microprocessors are becoming more and more popular along with lower prices and increased solidification, which means that MCUs are increasingly seen as products. Despite this commercial trend, vehicle control system design engineers still feel that there are very significant differences between different control boards, including various levels of processing speed and output power provisions. The selection of MCU can generally reduce the cost of raw materials (BOM), which in turn can reasonably reduce the price of the electronic device manipulation module (ECU) itself.

One other major factor to consider when selecting an automotive MCU is to find a company with a long history and a large market share. It is also important to consider whether the distributor can offer a wide variety of MCUs for a wide range of vehicle applications, including body, switching power rails and interceptor information management systems. Look for a vehicle product line that includes 16-bit and 32-bit automotive MCUs based on industry-certified, proprietary CPUs and standard ARM architecture.

3. Top 10 Considerations for Choosing an Automotive MCU

In automotive applications, microcontrollers (MCUs) provide critical performance. With the reduction of price and the increase of the whole solidification, etc., MCUs are gradually becoming commercialized. However, there are still significant differences for different MCUs, so it becomes especially important to choose the right automotive MCU to reduce costs without compromising the required performance.

Microcontrollers (MCUs) provide critical performance in an increasingly wide range of automotive applications from motor control, to infotainment systems and body control. Microcontrollers are becoming more popular as prices fall and solidification increases, meaning that MCUs are increasingly seen as commodities. Despite this trend toward commoditization, automotive system design engineers still see significant differences between controllers, including various levels of integration and power requirements. Choosing an MCU can often trim down the cost of materials (BOM), effectively reducing the price of the electronic control unit (ECU) itself.

When selecting an automotive MCU, design engineers can consider the following 10 important factors to achieve a balance between cost pressures and the specific performance characteristics required by the application.

1. Low voltage detection

One of the risks of failure during MCU operation is the possibility of the supply voltage or the MCU internal voltage dropping below the desired level at critical points. Obviously, this can cause a failure if the operating voltage is not guaranteed and goes beyond the recommended supply voltage.

Conventional systems use an external voltage monitoring IC to check the voltage. However, this function can be integrated into the MCU by an internal block that monitors both the MCU's internal voltage and the external supply voltage level. As shown in Figure 1, the MCU is automatically reset when the voltage drops below a preset threshold level. The threshold level can be selected from a set of pre-set values (7), as is the case with Fujitsu's latest MCU products. This method allows external components to be removed from the BOM, thus reducing costs.

2. Watchdog Timer

Another important feature to consider is the watchdog timer (WDT), which helps to recover from fault conditions such as "runaway microprocessor" or "processor in clutter". In the past, embedded systems used external ICs to perform this function, but it is possible to integrate multiple watchdog timers in the MCU. For example, one timer can work as a separate clock external to the CPU OS clock. This timer would be based on the slower CR clock and would be suitable for use as a hardware watchdog for the MCU, or for longer software loops to prevent runaway conditions. Another timer could be based on a faster peripheral clock. Theoretically, the watchdog timer would support a window function when the timer may be feeding back too fast due to some error condition, which would also reset the MCU.

3. Dedicated NV memory

As with the watchdog timer, EEPROM has traditionally been an external device to the MCU. However, it is possible to turn such memory devices into internal devices by using dedicated ROMs. The internal EEPROM can be further enhanced by improving stability and adopting error correction mechanisms.

An advanced way to integrate EEPROM internally is to use flash memory with dual-operation capabilities. One part of the flash memory bank can be read while the other part of the bank can be programmed to implement the EEPROM through a single flash module. another approach is to implement two flash modules, although the overhead of this approach will be higher than that of dual-operation flash. For example, Fujitsu MCUs have a high reliability EEPROM solution with up to 100,000 erase/program cycles. These MCUs also support ECC, which can retain data for up to 20 years. Commercial-grade software for controlling flash memory to EEPROM functionality is now available.

4. Automotive grounding

The electrical connections in the automotive environment are really very long due to the way the electronic control units are positioned. Automotive systems contain many ECUs and other devices that draw relatively large currents. As a result, in addition to the parasitic noise generated by the ECU itself, electrical grounding levels are often suboptimal and may drift over a range.

MCU design based on such a grounding condition will improve robustness and fail-safe levels. Advanced MCUs are often designed for standardized VILs based on automotive conditions. ECU quality is improved because the "floating ground" helps prevent errors.

5. Vbat level direct input

Some ECUs in automotive systems can handle I/O signals around the battery level voltage. For CMOS-based design semiconductors, the I/O signal is the maximum of the VCC level, typically in the range of 3V to 5V. Therefore, a converter is required to perform voltage level conversion. In some cases, voltage protection can be implemented, thus allowing high-voltage signals to be connected directly through current-limiting resistors. The Fujitsu MCU is designed to support this function with an internal protection diode and an external current limiter. This method reduces the number of components required on the PCB, thus further reducing costs.

6. Terminal function relocation

It is often challenging to maintain the smallest possible number of layers in the PCB layout for ICs with a fairly large pin count. peripheral components on the PCB cannot always be ideally positioned according to the pin distribution of the MCU. Sometimes it is useful if the MCU has the built-in flexibility to relocate its internal modules to another set of pins. This can be achieved through software settings. This capability can increase flexibility in the PCB layout process.

7. ADC auxiliary functions

Analog-to-digital converters (ADCs) have long been an essential functional block for embedded systems. ADCs convert signals from the analog domain to the digital domain, allowing access to information from the analog domain.

The ADC function block can be modified to differentiate the MCU based on the ADC function block according to the specific application. This enhancement can differentiate the entire MCU package. For example, the ADC block can support range comparator and pulse detection functions in hardware. These functions are useful for applications such as stepper motor control in dashboards, power monitoring, and sensor applications. ADCs can process input signals from stepper motor coils to perform zero point detection (ZPD). While the processing task is done in hardware, the CPU can use its MIPS elsewhere.

8. LIN Hardware Auxiliary Functions

The Local Interconnect Network (LIN) is a low-cost, low-speed communication technology that is widely used in body-on-frame applications. The LIN bus enables automatic frame header transmission and detection, communication test functions, variable interrupt length generation, and checksum generation and verification in hardware. Therefore, using the LIN bus helps to enhance MCU performance. This method helps to save MIPS of CPU when used elsewhere.

9. ZPD Enhancement

For dashboard applications, the ECU uses Zero Point Detection (ZPD) to determine when the pointer reaches the end point in order to stop the stepper motor. This function requires the stepper motor controller (SMC) to read and evaluate the voltage signal in the motor coil (also known as the "counter-electromotive force") in order to perform the detection. The SMC can be enhanced with additional hardware support to perform voltage evaluation so that no external components are required to implement ZPD. In addition, most counter-electromotive force evaluations can also be performed using hardware mechanisms. (In this regard, the ADC range comparator and pulse detection functions mentioned above are more useful.) In addition, this method requires only minimal CPU usage

10. Position and rotation counters

It is advantageous to provide the Quad Position and Rev Count Counter (QPRC) function in the form of a hardware block. This allows users to implement the jog-dial function in audio and navigation applications. This module controls the degree and direction of rotation and determines the speed of rotation. In theory, this could be achieved by employing a standard input capture unit in the MCU. However, implementing dedicated hardware modules dedicated to these tasks allows the CPU to conserve resources, resulting in better task allocation within the system and a simplified software package.

In summary, while commercialization of vehicle microprocessors tends to occur, automotive MCUs can still give a variety of different and unique roles that can enhance system software features, but not necessarily the cost. Careful selection of automotive MCUs can substantially improve the development potential to complete the final differentiation competition with high cost efficiency. Choosing a reputable MCU distributor with a wide variety of products and strong applicability will make the MCU design process increasingly easier and more efficient.