Discussion on Design Considerations for USB Type-C and PD Controllers in Vehicles

With the widespread availability of portable Electronic devices, users are increasingly charging their devices while driving. USB Power Delivery makes charging your device extremely convenient. The high data rates of USB also enable next-generation infotainment systems to support a wide variety of in-vehicle functions, such as audio playback, screen and app sharing, and data connectivity.

The traditional USB Type-A interface has been widely used in various models of automotive OEMs, and its power supply capacity is up to 7.5W (5V voltage, up to 1.5A current). With the rapid popularity of USB Type-C interfaces on PCs, smartphones and other portable electronic devices, USB Type-A interfaces are rapidly becoming obsolete. The USB Type-C semiconductor market is expected to exceed 900 million units shipped by 2022 (source: Gartner 2018 report and Cypress estimates).

Compared with the USB Type-A interface, the USB Type-C interface is more compact in structure, has a universal connection, can be plugged forward and backward, and has no directional restrictions on cable insertion (the plugs at both ends of the Type-C cable are exactly the same). In addition, it can significantly increase the output power, up to 100W (20V voltage, up to 5A current). Being able to deliver much more than 7.5W, it enables attractive new usage modes, fast charging, and the ability to simultaneously charge the ever-increasing number of active devices in the car, such as tablets, laptops and even electric shavers knife (see Figure 1).

Discussion on Design Considerations for USB Type-C and PD Controllers in Vehicles

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

To implant a USB Type-C interface with a new generation of power supply capabilities into a car involves much more than simply increasing the voltage and current of the power supply port. It also requires a different design method from the USB ports of commercial and consumer products. . In this article, we will discuss how to use USB in the vehicle, what 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 beauty of Power Delivery

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

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

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

Figure 2. To reduce cost, 100W of supply power can be shared among multiple ports, known as dynamic load sharing. A) A single device charges at 100W; B) After the second device is plugged in, the two devices can share the power provided by the port.

USB Type-C and PD Controller

To handle the complexities of the USB Type-C and Power Delivery (PD) protocols, the PD controller integrates an embedded microprocessor with PD logic. Typically, the microprocessor’s firmware is provided by the processor manufacturer, either as a downloadable file or directly generated by the development environment.

For automotive OEMs to provide highly reliable solutions over the long life cycle of the vehicle, USB certification is only a minimum requirement. The controller should be supported by a mature software stack and tested in the market, so as to ensure the reliability of the USB subsystem. In addition, interoperability is also necessary. Because two devices that conform to 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 grown into a major feature in cars, 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 how easily they can connect to their phones and play music than how well the engine is running.

Vehicles have a long lifespan, and they need to interoperate not only with virtually every smartphone, tablet, and laptop on the market today, but also with electronic devices that will be introduced in the next few years. Interoperability becomes even more important given that the average smartphone is replaced every two years.

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

The only way to achieve high reliability and interoperability is to use a programmable USB controller. Using a programmable controller facilitates the upgrade of the USB PD stack to interoperate with the latest devices. Because there are so many components in a car that need to run using software, drivers are accustomed to these software upgrades being transparent to the car owner. Because when a car is being serviced, technicians typically start by upgrading the firmware.

Although the controller has an embedded processor, it is not necessarily programmable. Take, for example, a fixed-function USB controller, which requires no programming and sells for a lower price. As an alternative, configurable controllers offer a limited number of pre-programmed configuration options.

Fixed-function and configurable controllers are well suited for applications such as consumer electronics devices such as USB mice. Such applications have a product lifespan of a few years at most, and product interaction is simple with a limited number of well-defined devices (such as PCs and laptops).

Because programmable USB controllers allow developers to take full advantage of the controller’s capabilities, it provides 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 a specific device. In addition, when new standards are introduced or unexpected problems occur, the 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, it is not necessary for developers to program the controller directly. Using advanced development tools, developers can define various operating modes of the controller. Next, the development tools can automatically generate the correct firmware. These tools also simplify the process of updating controllers.

In addition, some USB controller manufacturers manage the interoperability of new USB devices, providing firmware upgrades for USB-C ports in vehicles in response to changes in the specification. There is also no need for automotive OEMs to dedicate engineering resources to do this work themselves.

In-vehicle USB controllers are different from standardized commodities. Just imagine, if a USB mouse stops working, it can be replaced for less than $10. But if the car USB port stops working, expensive warranty repairs are required to restore it. Therefore, in-vehicle USB controllers must meet higher standards. Yields must be much higher than consumer products. Electronic equipment 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, consumer controllers may have short warranties, while automotive OEMs require more than 10 years of warranty.

Five Technologies for Ensuring Vehicle-Grade Availability

One of the main challenges in designing a USB Type-C subsystem with greater power delivery capability is that the power supply requires overvoltage, overcurrent, ESD and short circuit protection as well as high voltage gate drivers. In addition, cable compensation is also required to ensure the signal quality of the signal on the vehicle when it passes through the long cable. The interior space of the car is often cramped, and it often works in harsh environmental conditions. In order to achieve reliable operation, it is also necessary to add temperature control and control power to prevent overheating and damage. Additionally, in the transition to USB Type-C, OEMs need to support legacy USB Type-A devices.

Circuit Protection: In the real-world use environment of USB ports, USB circuits need to be protected against a series of electrical events. Among them, the most common is electrostatic discharge (ESD). For example, passengers moving back and forth on plastic chairs or rubbing carpets can build up electrostatic charges. If they touch the exposed USB ports, they can damage the delicate electronics in the car, which are difficult and expensive to repair.

To prevent ESD, the system needs to be connected to the shield ground so that the energy can be safely dissipated. Ideally, the controller should integrate ESD protection. Typically, 8 KV of contact discharge protection and 15 KV of air discharge protection are sufficient to protect the controller from damage due to ESD events. Additionally, additional ESD protection diodes can be added on the PCB to further enhance protection.

USB ports also need to be protected against accidental overvoltage (OV) and overcurrent (OC) conditions. Overvoltage and overcurrent often occur during device charging. When initiating charging, the device and power supply system should be consistent in current and voltage. However, if the system supplies the wrong voltage or current, an overvoltage protection (OVP) or overcurrent protection (OCP) circuit needs to be triggered to protect the device.

In addition, short-circuit protection is also necessary. When the cable is pulled at an angle, the Vbus pin may be momentarily shorted to one of the digital pins. Vbus can go as high as 20V, while digital pins can only withstand 5V, and this short circuit can damage the associated port. Short circuit protection is more important for USB Type-C ports than for Type-A ports. This is because the Type-C port packs 22 pins (compared to 9 for Type-A) in a more compact space, thus increasing the probability of shorting the Vbus.

Ideally, the USB controller should integrate short-circuit protection. Short circuit protection can be reset so that a short circuit does not damage the controller. The controller can then be reset to restore the Type-C port function, so that the short-circuit event becomes a temporary recoverable event, and there is no need to recall the vehicle to the store for repair. Without integrated short-circuit protection, the controller could burn out, causing serious problems.

High Voltage Gate Drive: To support backward compatibility, the default voltage of the USB Type-C interface is 5V. After the supply voltage is determined, the controller may need to switch from a 5V FET to a 20V FET to support a higher power supply. If this function is not integrated in the controller, additional circuitry is required to drive a higher power FET to provide 20V to Vbus.

Cable Compensation: For convenience, USB ports may be located throughout the vehicle, such as in the center console, in the center storage compartment between the rear seats, and/or in the glove compartment. For USB ports that are not only used for power supply (such as data functions), the USB controller is also likely to be used for infotainment systems. Connecting the port in the storage box to the infotainment system can require a USB cable of up to 10 feet. Using such long cables can cause severe voltage drops that can adversely affect signal quality and reliability.

To keep the signal quality in long cables within a reliable operating range, the controller can apply compensation. Simply put, the firmware inside the controller adjusts the output voltage to compensate for the differential voltage created by the extra long cables. This compensation can take a fixed value according to the length of the cable used, and the controller can also perform dynamic voltage drop compensation by regularly monitoring the received signal and modifying the compensation adjustment amount.

Over-temperature power control: Another challenge of adopting USB Type-C is how to solve the problem of generating a lot of heat when charging up to 100W power. Overheating can cause a range of problems, including starting a fire and/or damaging the device being charged. Adjacent, heat-sensitive components, such as electronics for infotainment or navigation systems, may also be adversely affected. Excessive heat dissipation can even destroy the USB port itself, requiring expensive maintenance or warranty.

Over-temperature power control is an effective way to prevent overheating. Thermal sensors placed next to sensitive components alert the controller when thermal thresholds are approached. The controller then reduces the charging power. When the power is reduced, the heat generation is reduced and the system can cool down. Meanwhile, the connected device is still charging, just at a reduced speed. This safety function should be integrated in the controller’s microprocessor and be transparent to the user.

Legacy USB Type-A support: While new devices will use USB Type-C, there are still billions of devices using USB Type-A. Automotive OEMs need to provide Type-A ports to support these legacy devices. Instead of designing two separate USB subsystems, existing controllers can support both Type-A ports and Type-C ports (see Figure 3). These all-in-one controllers minimize overall BOM cost while simplifying system design.

Figure 3 Hybrid controllers such as the CCG3PA provided by Cypress support both Type-C ports and Type-A ports, so users can connect both Type-C port devices and fast charging, as well as their traditional Type-A ports device and charge it.

In order to ensure the reliability of the power supply, all of the above functions need to be implemented. This will significantly increase the cost and space footprint of the in-vehicle USB Type-C and PD subsystems. A USB controller for the automotive market integrates these and other functions (see Figure 4), ensuring that all components are automotive-compliant, work well together, reduce cost, and simplify design. Reducing the number of components that need to be assembled also reduces potential points of failure and improves reliability.

Figure 4. A USB Type-C controller designed for the automotive market, such as the Cypress CCG3PA shown here, integrates the necessary components to ensure highly reliable power delivery, reduce cost, and simplify design while maintaining good performance over the life of the vehicle interoperability.

With USB PD fast becoming a standard feature in cars, interoperability with next-generation portable devices is key. The car needs to support the USB Type-C interface. Upgrading from USB Type-A to USB Type-C also supports new features such as fast charging. To maintain high quality and interoperability throughout the vehicle’s life cycle, designers need programmable controllers that are flexible enough to adapt to changes in the USB specification and interoperate with future products based on the new specification. By integrating critical functions into the controller to protect the internal electronics, OEMs can ensure reliability while minimizing system cost.

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