Resonant wireless charging - consumer applications
Resonant AirFuel (A4WP) 6.78 MHz, communication on Bluetooth low energy or in-band communication
The advantages of resonant designs over inductive ones is a clear improvement in user-friendliness: devices can be freely placed in the vicinity of the transmitter (typically >50 mm of vertical freedom), multiple devices of different size and input power can be charged in parallel.
Infineon's products take the lead in fast switching. With the best figure of merit (FOM) for gate charge times, RDS(on) and Coss they enable 6.78 MHz inverter designs. Superior power MOSFET technology addresses frequency switching implementations, especially in the 30V - 10V areas for class D inverter designs and in the 150V - 250V voltage class for class E inverter designs.
Rather than relying on an application specific IC for protocol and power delivery, the strength of the Infineon wireless charging solution lies in its modular software based architecture. Infineon’s XMC™ - SC wireless power controller based on the ARM® Cortex®-M0 core provides a powerful and cost-effective platform for high performance, smart and safe wireless charging applications.
On top of all, within Infineon’s portfolio the “coolest” driver ICs in the industry are already available as low-side drivers for class E implementations. And for transmitter designs using a pre-regulator (buck or buck/boost) to control the input voltage of the amplifier OptiMOS™ solutions can be found in the 20V - 400V MOSFETs section.
Two topologies to address resonant system requirements: class D versus class E amplifier
Gallium nitride (GaN) and wireless charging
Infineon has extended its technology leadership by adding gallium nitride to its offering. Now we are in the unique position to master all power technologies from silicon (Si) - superjunction MOSFETs, through discrete IGBTs and modules - to wide bandgap materials like silicon carbide (SiC) and gallium nitride (GaN).
Having optimized inductive wireless charging does not mean we have completed the job. To the contrary! Infineon is fully aware of the next big challenge: maximizing end user convenience by making wireless charging ubiquitous, and improving the freedom of positioning devices for getting charged. Consequently, high transmission frequencies (multiple MHz) will soon exceed the capabilities of even the most advanced silicon power technologies within the transmitter and the receiver devices, especially in class E designs.
Infineon’s engineers have worked extensively on this matter and have now released CoolGaN™. Due to its significantly reduced parasitic capacitances, it is the ideal choice for switching at frequencies in the MHz range (e.g. 6.78 MHz as required by the AirFuel Alliance wireless charging standard). CoolGaN™ is ideally suited to maximize overall system performance.
With CoolGaN™, Infineon launches a GaN enhancement mode high electron mobility transistor (e-mode HEMT) portfolio with industry-leading field performance enabling rugged and reliable systems at an attractive overall system cost. The e-mode (normally-off) concept is a single-chip solution and hence facilitates further integration either on the chip or package level.
GaN switch performance features low gate charge and excellent dynamic performance in reverse conduction compared to silicon FET options. This enables more efficient operation at existing frequencies, and much higher frequency operation which can improve power density by shrinking the size of passive components.
COSS is a critical design factor in wireless power transfer systems at higher frequencies and CoolGaN™ 600V e-mode HEMTs enable optimal tuning in class E amplifiers especially above 30 W. Only at lower power levels (<16 W) or in class D designs it is possible to use low COSS silicon MOSFETs. Infineon’s CoolGaN™ 600V e-mode HEMTs have been successfully tested in a class E wireless charging demonstrator as well as in customer implementations operating at 6.78MHz. Advantages of using CoolGaN™ 600V for higher power class E designs among many others would be - robustness, quality, reliability, very low gate driver losses, low QG compared to equivalent silicon MOSFETs and almost linear COSS without large increase at low VDS, enabling ZVS operation over a wide load impedance range.
More GaN products (including additional voltage classes) are in the pipeline, coming soon to the market.
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