5000-word article explains all aspects of car USB power supply

Summary: Charging convenience does not come for free. Engineers have come up with many solutions behind the scenes. Looking to the future, do not buy cars that do not support USB Type-C interface.

With the widespread popularity of portable electronic devices, users are increasingly charging their devices while driving. The USB power supply function makes device charging extremely convenient. The high data rate of USB also enables the new generation of infotainment systems to support a variety of in-vehicle functions, such as audio playback, screen and application sharing, and data connection.

The traditional USB Type-A interface has been widely used in various models of automotive OEM manufacturers, with a power supply capacity of up to 7.5W (5V voltage, up to 1.5A current). As the USB Type-C interface is rapidly popularized on PCs, smartphones and other portable electronic devices, the USB Type-A interface is rapidly being eliminated. The USB Type-C semiconductor market is expected to ship more than 900 million units by 2022 (Source: Gartner 2018 report and Cypress estimates).

Compared to the USB Type-A interface, the USB Type-C interface is more compact and has a universal connection that can be plugged in either direction, with no directional restrictions on cable insertion and removal (the plugs on both ends of the Type-C cable are identical). In addition, it can significantly increase the output power, up to 100W (20V voltage, up to 5A current). By providing power far beyond 7.5W, it can enable attractive new usage models, allowing fast charging and the ability to simultaneously charge the growing number of active devices in the car, such as tablets, laptops and even electric shavers (see Figure 1).

Figure 1. The power required to charge various devices and the USB specifications that meet the requirements.

To implant the USB Type-C interface with the next-generation power supply capability into the car, the work involved is far more than just increasing the voltage and current of the power supply port. It also requires a different design approach from the USB port of commodity and consumer products. In this article, we will explore how to use USB in the vehicle, the functions that USB Type-C and PD (Power Delivery) controllers should have, the impact of interoperability, and the main factors that should be considered in USB Type-C design.

The benefits of Power Delivery

The pace of our times is accelerating, and we need to be able to charge our devices faster and more frequently. With a 100W power supply, you can fully charge your laptop and mobile phone at the same time in about 15 minutes.

Improving power supply capacity is the key to in-car USB. Although users can use a Type-A to USB-C adapter to charge new phones through the old port in the car, this does not fully utilize the advantages of the USB Type-C interface. Although the new generation of mobile phones with USB Type-C interfaces have fast charging capabilities, they are limited by the 7.5W power supply capacity of the USB Type-A interface. Obviously, full power supply will play an important role in customer satisfaction and vehicle differentiation advantages.

Generally speaking, automotive OEMs do not need to provide full 100W power to every USB Type-C port in the car. In order to reduce costs without seriously affecting charging time or reliability, 100W of power can be shared among multiple ports to achieve so-called dynamic load sharing. With a total power of 100W, the USB PD controller can intelligently allocate the power of one USB Type-C port to 60W when a second device is plugged in, with the corresponding firmware, while the second plugged in device can get 40W (see Figure 2).

Figure 2. To reduce costs, 100W of power can be shared across multiple ports, a process known as dynamic load sharing. A) A single device is charging at 100W; B) When a second device is plugged in, both devices can share the power provided by the port.

USB Type-C and PD Controller

To handle the complexity of USB Type-C and Power Delivery (PD) protocols, PD controllers integrate an embedded microprocessor with PD logic. Typically, the firmware for this microprocessor is provided by the processor manufacturer, either as a downloadable file or generated directly by the development environment.

For automotive OEMs to provide highly reliable solutions over the long life cycle of vehicles, USB certification is only the minimum requirement. The controller should be supported by a mature software stack and pass market testing to ensure the reliability of the USB subsystem. In addition, interoperability is also necessary because two devices that comply with the USB specification may not work together.

Interoperability plays an important role in automotive applications, and poor interoperability can negatively impact user satisfaction. USB ports have evolved into a critical feature of automobiles, with more and more functions using USB ports, from charging and music streaming to smartphone interaction. When buying a car, people are sometimes more concerned with being able to easily connect their phone and play music than with how well the engine runs.

Cars have a long lifespan, and they need to interoperate not only with nearly every smartphone, tablet, and laptop on the market today, but also with the electronics that will be introduced in the next few years. Interoperability becomes even more important when you consider that the average smartphone is replaced every two years.

In addition, like many standards, the USB PD standard will evolve over time. For example, the current standard supports Power Delivery 3.0 with Programmable Power Supply (PPS) and Quick Charge (QC) 4.0. If either of these specifications change (in fact, the USB Type-C specification and PD specifications are always changing), the car may not be fully compatible with new devices on the market.

The only way to achieve high reliability and interoperability is to use a programmable USB controller. Using a programmable controller helps upgrade the USB PD protocol stack so that it can interoperate with the latest devices. Because there are so many components in the car that need to run with software, drivers are used to the fact that these software upgrades are transparent to the car owner. Because when a car is serviced, technicians generally start by upgrading the firmware.

Although a controller has an embedded processor, it does not necessarily have programmability. For example, a fixed-function USB controller does not require programming and is sold at a lower price. As an alternative, a configurable controller provides a limited number of pre-programmed configuration options.

Fixed-function and configurable controllers are well suited for applications such as consumer electronics (e.g., USB mice), where the product lifespan is a few years at most and the product needs to interact with only a limited and well-defined number of devices (e.g., PCs and laptops).

Because programmable USB controllers allow developers to fully utilize the functions of the controller to provide the best experience for interoperability of multiple devices and various use cases. Through feedback, the controller can dynamically adjust and tune its own settings to optimize performance for specific devices. In addition, when new standards are introduced or unexpected problems occur, this USB controller is flexible enough to solve these problems through firmware upgrades. This helps automotive OEMs ensure interoperability, quality and reliability throughout the life of the vehicle.

It is worth mentioning that to fully utilize the functions of this controller, developers do not need to program the controller directly. Developers can use advanced development tools to define the various operating modes of the controller. Then, the development tools can automatically generate the correct firmware. These tools also simplify the process of updating the controller.

In addition, some USB controller manufacturers are also responsible for managing the interoperability of new USB devices and providing firmware upgrades for the USB-C ports in vehicles to cope with changes in specifications, so there is no need for automotive OEMs to dedicate engineering resources to do this work themselves.

Automotive USB controllers are not like standardized commodities. If a USB mouse stops working, you can replace it for less than $10. But if a car USB port stops working, it will require expensive warranty repairs to restore it. Therefore, automotive USB controllers must meet higher standards. The yield rate must be much higher than consumer products. Electronic devices for automotive applications must be able to withstand higher operating temperatures. The warranty period of automotive components is much longer than that of ordinary consumer electronics. For example, the warranty period of a consumer controller may be very short, while the warranty period required by automotive OEMs is more than 10 years.

Five technologies to ensure automotive-grade usability

One of the main challenges in designing a USB Type-C subsystem with greater power supply capability is that the power supply requires overvoltage, overcurrent, ESD and short-circuit protection as well as a high-voltage gate driver. In addition, cable compensation is required to ensure the signal quality of the signals in the car when they pass through long cables. The interior space of the car is often cramped and often works in harsh environmental conditions. In order to achieve reliable operation, temperature control and power control are also required to prevent overheating and damage. In addition, in the process of transitioning to USB Type-C, OEM manufacturers need to support traditional USB Type-A devices.

Circuit protection: In the real-world use environment of USB ports, USB circuits need to protect against a range of electrical events. Among them, the most common is electrostatic discharge (ESD). For example, passengers will accumulate static charges when they move back and forth on plastic chairs or rub against carpets. If they touch the exposed USB port, they may damage the delicate electronic devices in the car, which are difficult and expensive to repair.