12 Jan 2015

Wireless Charging for the Automotive Environment

Denis Ruffieux, of Melexis reveals how how wireless charging technology can be used for the automotive environment.

As the items of electronics that we all carry around with us become ever more complex, possessing an increasing breadth of features and functionality, the strain being placed upon their power resources is heightening.

Utilisation of wireless induction as a means to replenish the batteries of portable electronic goods looks set to see huge uptake in the near future, allowing users to avoid the inconvenience of carrying multiple cables or having to search for power points.

It is likely that this technology will soon be seen in domestic, retail and office settings. Automotive is another area where it could in time bring major benefits, under the right circumstances, enabling drivers/passengers to top up the charge levels of their portable devices while travelling.

Wireless charging predictions

Industry analyst firm IHS has predicted that the wireless charging market could be worth in the region of $8.5 billion by 2018. The roll-out of wireless charging infrastructure is already starting to get underway in shopping malls, hotels, airports and restaurants (earlier this summer, for example, coffee shop chain Starbucks announced its plan to implement wireless charging facilities in 8,000 of its outlets across North America).

Global Wireless Power Market - Source IHS Research

Figure 1: Global Wireless Power Market - Source IHS Research

With regard to deployment of such infrastructure within the next generation of car models, in principal it would be done in the same way as in any other setting, but there a few key points where it differs. Firstly, in other scenarios the charging equipment is connected to a mains supply, but here the charging is dependent on the battery inside vehicle to serve as its power source, so every effort must be made to limit power consumption (otherwise the problem is just being moved further along the chain with the portable device’s battery gaining prolonged operation, but doing it at the car battery’s expense).

Furthermore, there is the issue of RF radiation inside the cabin. This must also be kept to a minimum, especially with the growing number of wireless emitters (Wi-Fi hotspots, mobile phones, etc.) now being placed there, on top of the electro-magnetic interference (EMI) that is simply to be expected in automotive applications.

It should be noted that there are adequate handshaking mechanisms built into the wireless charging standards that have already been developed to allow their implementation in the everyday applications already outlined. Through such mechanisms portable electronic devices which are compatible can be identified and charging subsequently instigated. Unfortunately when directed towards automotive use, the impact that these represent on the vehicle’s battery is significant. There is, as a result, a clear need for an alternative approach.

Handshaking mechanisms

Already established as a highly popular wireless standard, Near Field Communication (NFC) could prove to be a very effective method by which induction charging might be initiated within automobiles. This secure, short range communication standard is highly suited to access control and point-of-sale systems. It does not have anything like the same sort of impact on power budget that other standards do, thereby making it more suited to wireless charging implementations that are reliant on a battery.

Since it has already been designed into a large proportion of the latest wave portable electronic products - including the most recent incarnation of the Samsung Galaxy smartphone, as well as the Nokia Lumia and just a few weeks ago the iPhone 6 (although this is on a restricted level so far), there aren’t any engineering challenges to overcome here that would hold back its adoption for initiating charging. It’s a similar situation on the automotive side too - where engineers are also seeing the appeal of NFC.

Within a vehicle it could facilitate the undertaking of a multitude of different tasks. These include access control, automatic identification of the user so that the lighting and seating can be configured to their personal preferences, or pairing of the mobile device to the media centre inside the car. If NFC has to already be included into both the automotive and the portable electronic device’s design for other reasons, then there is a very strong argument for employing it to take care of initiating wireless charging as well.

Through NFC a very low power wireless link can be established within the vehicle cabin. It can be kept running continuously with negligible effect upon the battery or any noticeable increase in the RF radiation present.

The vehicle is thus able to detect the presence of a compatible portable electronic device and then carry out handshaking, so that the wireless charging process can be put in motion.

Multi-protocol transceiver

Operating in the 13.56MHz frequency band, Melexis’ MLX90132 (see Figure 2) is an automotive grade (AEC-Q100 complaint), multi-protocol transceiver IC with low power operation. Its transmitter element has the capacity to deliver 300mW of RF power to an appropriate antenna load. Supporting Reader/Writer, Peer-To-Peer (Initiator and Target) and Tag emulation communication modes, this device has embedded Field and Tag detectors. The highly integrated dual driver architecture that it employs enables the number of external components needed to support it in an NFC design to be kept to a minimum.

Functional Block Diagram for Wireless Charging System

Figure.2: Functional Block Diagram for the MLX90132 from Melexis

In partnership with Freescale Semiconductor, Melexis has gone on to develop a reference design for automotive wireless charging which is based on the MLX90132. The WCT-5WTXAUTO (shown in Figure 3) includes all the hardware and software drivers needed to create a fully functional wireless charging system from a single, cost-effective, simple-to-use module. The embedded NFC stack is controlled via a standard compliant NFC controller interface (NCI) and driven by a standard compliant upper NFC software stack.

Wireless Charging Reference Design Developed

Figure.3: The WCT-5WTXAUTO Wireless Charging Reference Design Developed by Melexis & Freescale

As well as a MLX90132, the reference design makes use of a Freescale MWCT1003AVLH microcontroller. This supports the NFC low-layer stack and a leading-edge wireless charging system, also developed by Freescale.

NFC antennas for wireless charging

The on-PCB printed NFC antenna addresses the detuning caused by close proximity to wireless charging coils. As both stacks are contained inside one microcontroller, better co-existence between the two technologies is witnessed – with sequential operation of the NFC and wireless charging activities. Thanks to its embedded field and tag detectors, the reference design’s power consumption is extremely low. Furthermore, the proprietary Electro-Magnetic Disturbance (EMD) algorithm enhances performance levels for both Reader/Writer and Peer-to-Peer modes.

The regularity with which recharging of portable electronic devices needs to occur has increased significantly as the number of functions being packed into such products continues to rise. Widespread proliferation of wireless charging could radically change the face of the consumer electronics sector and its value as a new feature is being recognised by car manufacturers - allowing them to differentiate their models for those of their rivals. The growing presence of NFC in both handsets and vehicles means that automotive engineers will be able to implement a more effective, energy efficient way by which wireless charging can be achieved.

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About the author

Based in Neuchâtel Switzerland, Denis Ruffieux is a product line manager for Melexis, having worked for the company for 12 years. Denis is responsible specifically for the company's NFC product offering. He has an Electronic Engineering diploma from the Haute Ecole d'Ingénierie et de Gestion du Canton de Vaud (HEIG-VD).

Melexis Microelectronic Systems manufactures microelectronic integrated systems. Melexis has a wide range of standard products for both automotive and industrial applications. The company is also involved in many cutting edge new development areas such as: TPMS (tire pressure monitoring), acceleration sensors, solid state gyroscopes, automotive CMOS cameras, heads-up-displays (HUD), optical bus, integrated LIN micro-controller family, 360-degree position sensing, ultra high-voltage (650V) engine ignition IC’s, and many others. Their ongoing commitment to R&D in new product areas keeps Melexis customers ahead of the competition.

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