The Qi open standard for wireless power transfer developed the Wireless Power Consortium has come a long way since its introduction in 2008, when it enjoyed only limited support among manufacturers — Apple, the maker of the iPhone, was perhaps the most notable holdout until the company announced its support for Qi in 2017. As of December 2023, the WPC reports that over 350 manufacturers are working with the standard, which allows compatible devices such as smartphones and tablets to charge their batteries when placed on a charging pad.
Still, barriers remain to widespread adoption of wireless charging technology — including the speed of charging compared to traditional wired methods, the cost of both charging stations and components inside devices, limits on wireless charging infrastructure and the fact that, while it’s the front-runner, Qi is not the only standard out there.
ST Microelectronics’ recent introduction of evaluation boards designed to simplify the development of Qi-compliant wireless chargers may help to lower those barriers. The STEVAL-WLC38RX board, based on the STWLC38 receiver IC, and the STEVAL-WBC86TX, based on the STWBC86 transmitter IC, can each be leveraged toward rapid building and testing of wireless charger prototypes. To assist development, both are also compatible with the company’s STSW-WPSTUDIO graphical software environment.
The STWLC38 receiver IC supports the Qi 1.3 15W Extended Power Profile (EPP) and 5W Baseline Power Profile (BPP). It can also perform as a 5W transmitter and allows reverse power transfer for device-to-device charging. Integrating a synchronous rectifier and low-dropout (LDO) linear regulator, the IC converts power from the receiver coil to a programmable 4 V to 12 V DC output voltage, with power-transfer efficiency of 85%. ST’s Adaptive Rectifier Configuration (ARC) mode, which maximizes the usable charging area, extends the typical receiver-detection distance by 50% and increases spatial freedom to position devices for optimal power transfer.
The STWBC86 Qi 1.2.4 BPP-compatible 5W transmitter integrates a high-efficiency, low-impedance full-bridge inverter and drivers to ensure low power dissipation and minimize the bill of materials. The IC controls the energy transferred through the transmitter coil by adjusting the applied PWM frequency and duty cycle.
Both ICs operate with a wide input-voltage range, and each is dynamically managed with an Arm Cortex-M0+ digital core for optimum efficiency. Integrated non-volatile memory (NVM) permits hosting advanced features and allows protocol evolution by updating firmware. In addition, both ICs are housed in tiny chip-scale packages, making them suited for use in very compact applications. Thermal management and electrical protection are built in.
Perhaps most significantly, smartphones and tablets are just the tip of the iceberg in terms of applications for the new evaluation boards. Both can accelerate the development of solutions based on the transmitter and receiver ICs for a wide range of consumer, medical, and industrial applications — including smartphones, tablets and smartwatches and other wearables, plus personal medical devices, drug-delivery devices, portable ultrasound devices, toothbrushes, shavers, computer peripherals, hearing aids, charging cases, power tools and mobile robots.
