Key design considerations for in-car wireless charging

January 24, 2018 Majeed Ahmed, Automotive Contributor

In-car wireless charging is growing in popularity, and the sense of urgency to develop viable solutions in this area was palpable on the CES 2018 show floor. There, chipmakers like Infineon and ON Semiconductor unveiled in-vehicle wireless charging designs.

ON Semi has partnered with ConvenientPower Systems (CPS) to create a turnkey in-vehicle wireless charging solution. The inductive charging design from CPS employs ON Semi's NCV6500 power management controller, which incorporates protection features such as coil voltage sensing, bridge current sensing, and over-voltage and over-current protection.

Likewise, Infineon showcased how its reference designs for both inductive and resonant wireless charging work alongside the company's AURIX and XMC microcontrollers.

Figure 1. System diagram of Infineon's wireless in-car charging design.

The quest to develop in-cabin wireless charging systems comes with daunting design challenges related to power transfer and heat management. Add to that strict automotive safety, security, and environmental requirements.

Below are key design considerations specific to in-car wireless charging systems.
Figure 2. Architecture of a wireless charging design.
 
  1. Safe charging mats – Foreign object detection (FOD) enhances device detection accuracy and ensures safe operation in safety-conscious automotive designs. It cuts power to prevent overheating if objects containing metal are brought too close to the charger.
  2. Free positioning – Another critical design consideration is free positioning, which mandates a broad charging field for providing a ‘drop-and-charge’ experience for users. It allows drivers and passengers to simply place the device in the designated area such as a tray in the center console or the glove box.
  3. Power efficiency – In-cabin wireless charging designs demand greater power efficiency and thermal management while carrying out power conversion and transfer tasks. Carefully selecting components like voltage regulators and power MOSFETs can ensure wireless charging performance and efficiency.
  4. Shielding interference – It's imperative that a wireless charging power supply doesn't interfere with other in-vehicle systems and that the power-stage architectures feature robust electromagnetic interference (EMI) performance, especially when it comes to communications with vehicle buses such as CAN, LIN, and RS-232.

  5.  

    Multi-protocol designs – Almost all prominent smartphone vendors have adopted the Qi standard, but as the above-mentioned reference designs show, chipmakers are mostly supporting both the Qi and PMA standards.

  6. 15 watt sweet spot – First-generation 5W designs came into vehicles a couple of years ago, but carmakers are now quickly adopting above-5W wireless charging solutions. Wireless charging designs built around 15W offer three times faster charging of smartphones.

     

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