Everything You Need to Know about Wireless Charging

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1 Everything You Need to Know about Wireless Charging Adi Shieber, Yan Vainter - Freescale Semiconductor Abstract - Wireless charging is a very popular topic these days. We already instinctively think of mobile phones when we think of wireless charging, but wireless charging is of more than that. In this article we will introduce the concept of wireless charging, the benefits of having a standard for it, highlight the different wireless charging protocols being proposed, their benefits and where wireless charging is getting the best market traction. Wireless charging promises to free up consumer from using cables to charge their portable devices. Telecom operators and phone makers are adopting this technology. In car wireless charging could well be the last piece of wireless technology needed to finally enable a great smartphone application integration into the car. But several entities are competing to establish a standard, including Qualcomm, Samsung, Intel, Powermat, Nokia, Docomo and many others. Wireless charging is not a new idea, nor a new technology but it is getting more headline news lately with new smartphones announced including wireless charging feature such as the new Nokia Lumia 920 or the LG Nexus 4. Palm had shipped its Pre phone some 4 years ago with wireless charging build into the phone; but since then Palm has retrieved from this market. Powermat has been shipping in the USA wireless charging accessory systems for Blackberry or iphone for many years. And many of us have electronic tooth-brushes at home that charges wirelessly. So what has changed to make wireless charging appear more in the new headline? A wireless charging standard has appeared; actually maybe a few standards as we will see later. A standard brings many benefits to a market. First a standard ensures compatibility. A charger from company A will work with a device from company B and vice versa. A classic example is the phone system where any phone in the world can call any other phone on the planet. We take this for granted but without a global standard, this would not work. Then a standard means that competition will be there; bringing many benefits such as lower price and innovation. Indeed companies will need to innovate to differentiate their products on the market. Guarantee of supply is another benefit; one company may stop supplying products, another one will take place. A standard puts in place certification procedure with independent test labs. Finally a standard brings confidence. Customer will not invest in products that do not have a future. A standard means that current products will also work with future products as backward compatibility as guaranteed by the standard certification process. All these benefits that a standard brings are the key ingredients for consumer acceptance and for the market to grow. With the appearance of wireless charging standard, market analyst have been forecasting very high market growth. A series of report in 2010 from analysts such as ABI or isuppli were

2 forecasting a market take off in 2012 and quickly several hundred millions pieces shipped in More recent report such as the one released by IMS Research, suggests that more than 100 million devices with wireless power will be shipped in 2015, with the market worth of $5billion by It is now apparent that the analysts were too optimistic in 2010 underestimating the time for a standard to develop, for certification process to be in place and for the market to adopt it. But the one thing that did not change is the long term vision of a massive adoption of wireless charging for smartphones, tablets and other consumer devices. The market analysts have shifted their hockey-stick market growth forecast by about three years but have not changed their long term optimistic view point. The Wireless Power Consortium (WPC) announced in September 2012 that 8.5 millions smartphones have shipped with wireless charging feature integrated as per the Qi WPC standard. The adoption of wireless charging will increase more dramatically with the integration of the wireless charging circuitry inside the phone. Instead of having to add a special sleeve or back door, wireless charging circuitry is now getting integrated into the phone as a build in feature. Phones such as the Nokia Lumia 920 or the LG Nexus 4 are good example of this new trend. This integration decreases dramatically to cost of this function for the consumer and remove any extra thickness associated with after-market back doors or sleeves. Phone makers will also ship simple and low cost wireless charging mats with these phones, providing a simple out-of-the-box experience. Smartphones will drive the growth of this technology and represent the largest market in volume for wireless charging components. The wide scale adoption of wireless charging into smartphone will also drive a large number of accessory products such as wireless audio speakers like the JBL or TDK products. These wireless charging speakers integrate three complementary wireless technologies: Bluetooth to receive audio files from the phone, NFC for automatic Bluetooth pairing and wireless charging to keep the phone charged. This combination provides a new user experience with automatic audio streaming from the phone to the speaker with no hardware connection and no pairing mechanism; simply put the phone down on top of the speaker. Other accessories such as wirelessly charging Bluetooth headset have also been announced; wirelessly charging mouse for PC; or bed side alarm clock with wireless charging station build in. The proliferation of mobile device and consumer electronics with wireless charging build-in will stimulate the build-up of an infrastructure of public and private charging station. We start to see wireless chargers installed in airport lounges, coffee shops and hotels, and we will soon have these in public transportation and in our own vehicle. In future cars, there will be a wireless charger for your cell phone build into the car central console. Putting your phone on top of this surface will charge it, will automatically connected it to the car Bluetooth radio as well as connect your phone to a roof top cellular and GPS antenna for better communication while your phone applications and media files are transferred to your car infotainment display. The combination of these wireless technologies will provide the ultimate smartphone integration with your driving experience. All wireless charging system use the fundamental principle of current induced in a coil from magnetic fields. Sometime referred to as magnetic induction or resonant magnetic, some

3 difference in these systems is the coupling factor between the transmitting and the receiving coil. High coupling factors system means that both coils need to be in close proximity with good alignment. Some systems are designed with lower coupling factor enabling wider distance and freedom of placement of the receiver from the transmitter. The Wireless Power Consortium was started in 2009 to create a wireless charging standard called Qi. With about 200 members 5 years later and as many certified products, the WPC is in good position to achieve its original goal. WPC specifies transmitter topologies and ensure backward compatibilities with existing WPC receiver products. The transmitters can use one or several coils and in that latter case, one or several coils can be used simultaneously to generate the magnetic field. The first transmitter topologies are using close magnetic induction coupling and rely on using several (3 to 8) coils to enable X and Y spatial freedom. The Z distance between the transmitter and the receiver is typically 5mm. Lately the WPC has proposed a new transmitter type with 5cm Z spatial freedom using adaptive resonant magnetic principle, while keeping the backward compatibility with existing WPC induction coupled receivers. Another wireless charging standard Alliance for Wireless Power (A4WP) appeared in 2012 proposing resonant magnetic wireless charging system using the 6.78MHz ISM band to generate its magnetic field. The A4WP does not support the close induction coupling mechanism as the WPC. A notable difference between these two standards is the different frequencies used: 100 to 205 KHz for WPC and 6.78 MHz for A4WP. It is worth noting that the ISM band is also being used by other companies or consortium for wireless power transfer. For instance Intel has demonstrated prototypes of wireless power between a laptop PC and a cellular phone using MHz. The Eurobalise consortium has specified a wireless charging system between trains and fixed balise on the ground track using 27 MHz frequencies.

4 It is important to note that WPC, A4WP and to a lesser importance Eurobalise are consortium based, open standards for wireless charging. Worth noting from this table is that wireless charging system using ISM MHz bands have to rely on a different frequency band for energy transfer and for communication. This is surely due to the very narrow nature of the ISM band and the strict out of band emission requirements. The other important point is the ability or not for these technology to offer spatial freedom in the three dimensions for the placement of the receiver relative to the transmitter. WPC which started as a closely coupled system is now preparing an adaptive magnetic resonance transmitter topology to offer up to 5cm of Z spatial freedom, as well as similar or greater X and Y spatial freedom. A4WP and Intel appear to be offering similar type of system, while the Eurobalise standard distinguishes itself with its ability to transmit power wirelessly from a high speed train to a fixed balise on the tracks and get data back transmitted on a different frequency. How do these different systems compare then in term of efficiency, cost and compliance with emission standards. The following table attempts to give some guidance. The technologies have been regrouped per the frequency bands they are using. One on hand the WPC and Powermat systems that are below 500 KHz and the others using ISM bands at 6.78, or MHz. First it is of upmost importance for these systems to comply with regulation on human RF exposure and EMC radiation. There the below 500 KHz systems have better performance with more headroom to comply. With the ISM bands, we are still waiting to see concrete data showing that these systems do pass the FCC part15 and 18 as well as the CISPR11 requirements. The systems will surely manage to pass these requirements but the margins will be slim and may prove to be difficult to manage over time and high volume production.

5 On the other topics, efficiency, transmission range and system cost, all the technologies have some pros and cons which overall add up to similar performance. Driving circuitry will be more costly for ISM band system but will have cheaper coil/antenna while it is the opposite for below 500 KHz systems. Regarding transmission range and efficiency both frequency bands achieve similar type of performance, both obeying to the same laws of physics. So which system will be more prevalent in the market place? We truly believe that only an industry standard technology will be able to gain a widespread market acceptance. For the time being two open standard systems are: WPC and A4WP. The WPC Qi system surely has a head start with more than four years of existence and around 200 active members. WPC issued its first specification in 2011 and a subsequent 1.1 revision in A4WP started at 2012 and today they have around 80 members. WPC has the endorsement of the Japanese cellular phone companies and suppliers, Verizon in the USA, Nokia and many other consumer electronics companies. A4WP main members and founders are Qualcomm and Samsung. It is worth noting that both Samsung and Qualcomm are actually members of both consortiums. As a matter of fact there are more A4WP members, who are also WPC members and that ratio is likely to grow as more WPC companies will join A4WP to get access to its specification. The WPC has qualified several different certification companies that can deliver an official Qi certification stamp. By beginning of 2014, over 400 products had received Qi certification; up from about 120 products a year ago. This growth is tremendous compared to the growth of the year before. About two third of the WPC members are coming out of Asia, 20% from the USA and 15% from Europe which is also a good indication of regional adaption of this technology. WPC is now working a power extension of the current specification up to 15W; then a 30W system for tablets or small laptops. Finally a kitchen working group is looking at higher power up to 2000 Watts to wirelessly power kitchen appliances. Freescale joined the WPC in 2011 and has since produced several reference systems at 5W and 30W. One system demonstrates simultaneous wireless charging of four 30W battery packs; all driven out of one single MCU. Freescale utilizes a small Digital Signal Processor to implement wireless charging transmitter. The DSP functionality allows low power and fast processing of the PID loop required to drive the transmitter coils. The extra power processing of this small but powerful core can then be used by the system developer to implement other auxiliary functions such as CAN interface, user interface functions or any other functions that can use the spare memory space and I/O available. We are today at a turning point for wireless charging adoption as a mainstream technology. The ingredients for success are in place, standard(s) are there, large OEM and wireless operators are committed to the technology. Analysts are still forecasting a huge market growth, although a few years later as originally anticipated. Besides cellular phones and consumer devices, many other devices in other industry can benefit from the advancement in this technology even in places where a standard is not required or even desirable. Portable health equipment, toys, hearing aids, robotics, professional audio equipments, two way radios and many other systems could use wireless charging or wireless power transfer. With a solid supply chain of solution

6 providers these specific applications will find plenty of suppliers with solutions. The technology is there, the ecosystem is in place, one unknown still is what will Apple do with wireless charging? This might be the last piece of uncertainty for this market to finally take off.