What is a Domain Control Unit (DCU) used in autonomous driving technology? - Group of devices that contribute to higher performance -

ADAS stands for advanced driver-assistance systems. The systems aim to improve driving safety by assisting drivers with driving. On the other hand, AD refers to autonomous driving, in which the AD system takes the initiative and drives automatically instead of humans.

Autonomous driving is defined by the SAE (Society of Automotive Engineers in the US) as level 0 to 5. From level 0 to 2, driving relies on human drivers, while levels 3 and above allow the driving to be controlled by the vehicle.

A sensor ECU, main ECU, and actuator ECU are required to implement ADAS and AD.

• Sensor ECU：Senses the surrounding environment, etc. (camera, RADAR, LiDAR, ultrasonic sensor, etc.)
• Main ECU：Data processing, decision-making, etc. (ADAS-ECU, AD-ECU, DCU, etc.)
• Actuator ECU：Performs and assists the driving operation (accelerator, brake, steering, motor, engine, etc.)

The system flow from sensing to operation is shown in Figure 1 below.

Domain and zone types

System configurations for ADAS and AD include a domain type (distributed) and zone type (consolidated).

• Domain type: Each function is classified into a group referred to as a domain, and ECUs are consolidated in each domain. Each domain is connected to other domains via the Gateway, and data processing is carried out in each domain ECU.
• Zone type: ECUs are consolidated at each key locations in the vehicle body. In addition, a central computer is installed in the center of the system, where data collected from the key locations is processed and handled.

What is a DCU for ADAS and AD?

Each functional domain has a separate DCU (Domain Control Unit) (e.g. ADAS/AD, communication, powertrain, body, cockpit). Each DCU is responsible for consolidating a large number of devices that are in the same domain, processing data and making decisions in an integrated manner, and operating vehicles and devices through data transmission/reception and coordination with other DCUs.

For example, various sensor devices are integrated in DCUs for ADAS and AD, and sensed data are comprehensively processed and assessed, thereby implementing safe driving assistance and autonomous driving operations.

DCU market and equipment trends

The number of vehicles equipped with DCUs for domain type systems is expected to increase, mainly for autonomous driving levels 2 and below. As the level of autonomous driving increases further, the number of sensors installed must be increased accordingly to acquire data on the surrounding environment. As the number of sensors increases, the amount of data processed by DCUs increases, and the power consumption of the main semiconductor device that performs data processing increases with higher performance.

It is believed that devices for DCUs require "high current," "low loss," "miniaturization," "high frequency operation," and "high precision (voltage)."

DCU system configuration

Overview

The DCU and its peripherals are connected as shown in Figure 3 below. The inside of the DCU is made up of transceiver circuits that communicate with sensor ECUs or other DCUs, an SoC (System on a Chip) that processes data from sensor ECUs and makes decisions, various memories, an MCU that controls driving based on the information assessed by the SoC, and DC/DC converter power supply circuits required to operate these various circuits.

Transceiver I/F

As shown in Figure 4, a transceiver circuit uses two lines to communicate with external devices (CAN, Ethernet, etc.). During communication, when noise or static electricity enters from the communication lines, this may lead to a failure of the transceiver IC. Therefore, it is common to configure a transceiver circuit with a chip varistor and an ESD suppressor to prevent static electricity.

【Components used】

Static electricity measures: Chip varistor, ESD suppressor

POINT

1. ❶ Contributes to the suppression of electrostatic (ESD) noise while maintaining circuit communication quality with a lineup of products having a wide range of capacitance characteristics.
2. ❷ Chip varistors support low to high communication speeds with capacitance characteristics ranging from 8 to 250 pF.
3. ❸ ESD suppressors support high-speed communication speeds with their capacitance characteristics of 0.1 pF.

DC/DC converter

(1) What is a DC/DC converter?
A DC/DC converter refers to a circuit that converts a DC voltage into a different DC voltage. Since the required voltage values differ for each circuit in DCUs, conversion to the appropriate voltage is necessary. It is common to configure a DC/DC converter circuit with FETs, coils, and capacitors.

(2) Circuit configuration by load type
The circuit configurations of DC/DC converters differ depending on the power, voltage, current, and load transient response to be handled. As shown in Figure 5, there are three main types of circuit configurations.

＜TYPE A＞
Due to the very large current values, multiple coils and FETs are used to share the load current (multiphase). In addition, since the voltage drops when sudden current fluctuations occur instantaneously, polymer capacitors are used in addition to MLCCs (ceramic capacitors) to prevent voltage drops.

＜TYPE B＞
Capacitors with a large capacity are used in circuits with a large current flow. Similarly to Type A, polymer capacitors are used in addition to MLCCs (ceramic capacitors).

＜TYPE C＞
This is a general DC/DC converter circuit.

It is common for DC/DC converter circuits to use conductive polymer hybrid aluminum electrolytic capacitors for noise reduction at the input and smoothing at the output, automotive power inductors for voltage conversion, and chip resistors (high-precision chip resistors) for voltage measurements.

【Components used】

Noise reduction, switching, and smoothing ―― Conductive polymer hybrid aluminum electrolytic capacitor

POINT

1. ❶ Its high capacitance, low ESR, and high ripple performance contribute to circuit miniaturization and higher power features (low voltage and high current).
2. ❷ Improved capacitance characteristics at high frequencies contribute to the elimination of noise, including high frequency components generated by high frequency switching of circuits over a wide band of frequencies.

Voltage conversion ―― Automotive power inductor

POINT

1. ❶ Contributes to circuit miniaturization and higher power features (low voltage and high current) due to the low loss and high current performance of metallic magnetic materials.
2. ❷ Improved loss characteristics (low ACR) at higher frequencies contribute to the suppression of losses in high frequency switching circuits.

Voltage measurement ―― Chip resistor (high-precision chip resistor)

POINT

1. ❶ Contributes to the high-precision control of circuit output characteristics through the low resistance tolerance and low TCR performance with a thin-film structure.

Summary

The number of DCUs that are essential for the realization of autonomous driving is expected to increase in the future. This is because the higher the level of autonomous driving, the more sensors must be installed to acquire data on the surrounding environment. In the future, DCUs will be required to provide features such as "high current," "low loss," "high frequency operation," and "miniaturization" while reducing the power consumption of semiconductor devices. Aiming for DCU applications, Panasonic Industry offers a wide product lineup of highly functional devices that meet various requirements (Table 2).

Components	Features	Large current	Low loss	High frequency	Miniaturization
Conductive polymer hybrid aluminum electrolytic capacitors	Low ESR High-reliability	✔	✔	✔	✔
Automotive power inductor	High current, low loss High-reliability	✔	✔	✔	✔
Chip resistors (high-precision chip resistors)	High-precision, high heat resistance				✔
Chip varistors	Miniaturization and weight reduction				✔
ESD suppressors	Low capacitance Ultra high-speed data I/F			✔	✔