Reference Designs Take a Shot at Qi-compliant In-vehicle Wireless Charging

April 14, 2022 by Darshil Patel

As the Qi standard increases in popularity for wireless charging, Microchip and Renesas announce their Qi-compliant automotive-grade wireless power transmitter reference designs.

Charging electronic gadgets with wired chargers can be inconvenient at times. Therefore, in recent years, people have started adopting wireless technologies due to their convenience and simplicity. With various developments in wireless charging, or wireless power transfer (WPT), it is slowly becoming mainstream.


An example block diagram for wireless power transfer.

An example block diagram for wireless power transfer. Image used courtesy of Texas Instruments


There are many wireless charging technologies available; however, Qi, a wireless charging standard, is one example of a technology that is growing in popularity. With this trend in mind, semiconductor companies are now coming up with new Qi-certified solutions for consumer and automotive applications.

Recently, Microchip and Renesas released their Qi 1.3-certified reference designs for 15 W in-cabin automotive wireless charging solutions. These reference designs will help designers to build secure Qi-compliant automotive-grade wireless chargers.


The Qi 1.3 Wireless Charging Specification

The Qi 1.3 specification is an open standard released by the Wireless Power Consortium (WPC) to ensure high-quality wireless charging power transmitters and global compatibility.

This specification deals with several aspects of wireless power delivery, such as reliability, efficiency, communication between the transmitter and the receiver, and non-compatible device detection.

Differing from past versions, this new Qi 1.3 standard includes an additional authentication feature, in which the receiver inside the smartphone performs a one-way authentication to know if the transmitter is Qi-certified. The transmitter can cryptographically prove its compatibility. If the authentication fails, the phone limits the charging power to 5W or rejects the charging completely.

This new specification created demands for new highly-secure authentication devices. Hoping to spur Qi 1.3 designs forward comes reference designs targeting the automotive industry. 


New Qi-compliant Reference Designs

A reference design, much like how a recipe helps a chef, allows a designer to copy an IC-based design into their system without designing everything from scratch. Moreover, it saves the designer's time by eliminating some testing as the reference designs provide information about the circuit's performance under different conditions.

The new wireless transmitter reference designs are Qi-compliant and automotive-grade. Security and safety are crucial aspects of automotive-grade chargers, as a poorly designed charger can create a direct concern for the whole vehicle. Therefore, cryptographic authentication is an essential addition to the Qi standard, implementing trust between the phone and the charger. 

Microchip's reference design includes a digital signal controller, Qi 1.3 software stack, secure storage subsystems with cryptographic key storage, and the automotive-grade Trust Anchor TA100. The TA100 embeds multiple symmetric, asymmetric, and hashing security protocols that use reliable methods for cryptographic key agreement.


Microchip’s 15 W multi-coil wireless power transmitter block diagram.

Microchip’s 15 W multi-coil wireless power transmitter block diagram. Image used courtesy of Microchip


On the other hand, Renesas' P9261-3C-CRBV2 reference design relies on Renesas' proprietary FOD (foreign object detection) system. The solution is designed around the RH850 automotive MCU, the automotive-grade power controller P9261, and three MP-AP3 coils.

The design complies with the ASIL (Automotive Safety Integrity Level) B. The ASIL compliance is necessary for automotive chargers as the electric vehicles now have high-voltage power buses and high-energy batteries. Poorly functioning chargers can impact vehicle electronics and can be inherently dangerous.


A high-level view of Renesas' Qi-certified reference design.

A high-level view of Renesas' Qi-certified reference design. Image used courtesy of Renesas


Moreover, the transmitter can be controlled and monitored in real-time by a graphical user interface (GUI) that provides data on selected coils, transmission status, input voltage, output current, power, and bridge voltage. The GUI also adds flexibility in terms of programming and firmware changes. 

Similar to these solutions, Infineon released the automotive-grade wireless charging chip INFCSS202112 in December 2021. The chip consists of Qi-compliant authentication systems. It uses the OPTIGA Trust Charge Platform for WPC-compliant provisioning and cryptographic features for a high level of security. 

NXP also announced, earlier in October 2021, its automotive charging reference design consisting of a Qi-compliant MCU, CAN/LIN transceivers, and an optional NFC. It also featured a software package that allows complete customization for security and other parameters. 

The future trends in wireless charging are envisioned around electric vehicles. The advancements in security technologies will increase the adoption of wireless charging solutions even further.