USB Hub/Card Applications Hit The Road

March 24, 2010
USB is not only used to transfer data between devices, it also provides a means to charge portable devices.

USB interface

USB and flash memory cards have become ubiquitous in the consumer and industrial worlds. USB implements a high-speed serial bus that runs at up to 480 Mbits/s. Many operating systems provide native support for this technology with many hundreds of millions of devices shipped to date. USB is not only used to transfer data between devices, it also provides a means to charge portable devices.

As consumers expand their digital lifestyle to have their content always available, more and more devices take advantage of the economies of scale afforded by the explosion of interconnections that ensue. Car makers are embracing this trend as their vehicles integrate into the digital world.

Vehicles are also becoming storehouses of content and information. They can include large amounts of storage capacity for entertainment content and navigation information. One of the most popular memory formats today is Secure Digital (SD). The SD interface is also used in embedded applications to attach devices like Wi-Fi (or wireless local-area networks) and Bluetooth transceivers, as well as GPS receivers with an SDIO interface.

SD memory can be used to replace rotating media like hard disks, CDs, and DVDs. A state-of-the-art 32-Gbyte card holds the equivalent of close to seven DVDs. Car makers can use memory cards both as a connection to consumers and as a mechanism to upgrade different systems within the vehicle, be they navigation systems or any other devices that require software. Therefore, USB and flash media interfaces are very useful in automotive applications.


Before getting into the specific functions of the interfaces, let’s first consider automotive quality requirements. Devices intended for the automotive market have to be designed, validated, characterized, qualified, fabricated, and supported specifically for use in automotive applications. Cars have very long lifecycles, and any failure in the field is very costly in terms of repair time and customer satisfaction.

When ICs that are designed for consumer applications are used in automotive applications, they are often qualified according to the Automotive Electronics Council’s qualification requirements (AEC-Q100). This standard, however, only covers minimum common requirements for the qualification of an automotive IC. Many car companies and tier one automotive suppliers require extensive additional qualification tests, as AEC-Q100 alone does not lead to the ultra-low defect rates that they require.

In addition, AEC-Q100 primarily focuses on the qualification phase of the product cycle of an IC. Other phases such as the design and production of the IC, customer support, and the handling and investigation of returns are not covered in detail.

To reach the automotive goal of near-zero defect rates, all phases of the IC product cycle need to be addressed thoroughly. Before even looking at a product’s functions, automotive designers need to look at their supplier’s capability to deliver products with near-zero parts per million (ppm) defect rates.


Passengers use portable memory cards to transfer information created on computers, portable media players, or cameras to the car. Car makers also incorporate gigabytes of microcode into some of today’s most sophisticated vehicles. Further, they need to store map data for their navigation systems.

As mentioned earlier, solid-state memory is increasingly replacing rotating media inside automotive infotainment devices. Maps for a large country, like the United States, can fit in less than 2 Gbytes of storage. An SD card of this size can be purchased at retail for less than $5.00, making it very cost effective compared to the typical DVD player used for many automotive navigation systems. In addition, reliability is increased, as there are no moving parts associated with it.

The high-speed data transfer enabled by an SD interface can simplify software updates for other components in the car as well, like a head unit or other components.

These in-box use cases require true automotive-grade reliability. The new combination hub and card reader devices enable car makers to design highly reliable data access devices for their information and entertainment systems, whether those devices connect to internal peripherals or provide external consumer access.


A USB hub expands the number of available USB ports while the card reader provides memory card interfaces, such as SD/MultimediaCard (MMC) or Sony MemoryStick. The SD interface is standardized for memory applications. It also provides a generic input/output interface known as SDIO.

The SDIO interface uses the same electrical signals as the SD memory interface but can be used to attach modules that provide additional features such as Wi-Fi, Bluetooth, and GPS connections. It is even possible to build custom firmware to control new applications attached through SDIO.

It is important for the card reader supplier to have significant experience with memory cards manufactured by many different suppliers because the specifications for the SD interface allow some room for interpretation and optional features that can result in incompatibilities with different products. SMSC has performed extensive testing to support a large number of cards currently in the market.

The current devices also support using an external ROM to create secure memory formats or add customized applications based on system requirements. Incompatibilities with cards from different manufacturers could result in warranty claims against a car maker. Service calls are very expensive, so it is important to avoid them if consumers bring in a device that they got for free somewhere.

The combination hub/card reader function allows the placement of this device away from the main host controller to provide connectivity where it is needed. For example, the glove compartment or center console in a car could allow consumers to easily connect their devices without requiring long cables to the main head unit.


USB interfaces and storage memory provide useful enhancements to automotive systems. Automotive requirements result in stringent qualification processes that only a limited number of worldwide semiconductor suppliers can implement. They also result in special features being needed to simplify system design.

Flexibility in creating multiple platforms with a single platform is a plus. Car makers also require a very high level of compatibility when dealing with memory cards from multiple suppliers. And, the devices must be able to operate in a rugged environment with high temperatures and widely varying environmental conditions.

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