13.56MHz Wireless Charging Module White Paper

In recent years, in many application fields such as smartphones and smartwatches, the application of wireless power supply has become increasingly widespread due to the ability to eliminate charging ports and improve waterproof and dustproof performance. Similarly, in the field of small and thin devices, the demand for this very convenient wireless power supply function is also growing. On the other hand, factors such as antenna shape, size, and distance can affect whether the power supply function can be realized and its efficiency, so it is necessary to repeatedly conduct trial production, adjustments, evaluations, etc., on the entire electronic device before achieving wireless power supply. This makes the development burden in antenna design and layout design very heavy. Therefore, there is an increasing expectation in the industry for better universal wireless power supply standards and methods for small devices.

There are many wireless power supply methods, such as magnetic resonance (which transmits power by forming a magnetic field resonance between the transmitter and receiver resonators) and electromagnetic induction (which uses the induced magnetic field generated between the transmitter and receiver to transmit power). Among them, the 13.56MHz wireless charging using magnetic resonance has the characteristic of being able to use smaller antennas due to its high frequency.

The wireless charging module launched by ROHM is an integrated module of antenna and circuit board, supporting 13.56MHz, and can easily realize the wireless power supply function of small and thin devices.

Figure 1. Comparison of Wireless Power Supply Methods

The products introduced here, “BP3621” (transmitter module) and “BP3622” (receiver module), are the industry’s first (as of November 2021, according to ROHM survey data) small universal wireless charging modules using the 13.56MHz frequency band, providing up to 200mW of power supply. Moreover, by optimizing the antenna/layout design, a small-sized module of about 20mm to 30mm square has been achieved. Since it can significantly reduce the development time for trial production, adjustments, evaluations, etc., required to optimize power supply efficiency, it can easily realize the wireless power supply function of small and thin devices. In addition, the built-in antenna also supports bidirectional data communication and NFC Forum Type3 Tag communication, which will help expand the communication functions of application products.

Photo 1. Wireless Charging Modules “BP3621” and “BP3622”

Next, we will introduce the specific functions and effects of “BP3621” and “BP3622” (hereinafter referred to as “this product”).

This product adopts a unique matching adjustment antenna design technology, as well as a circuit board layout design technology that can reduce wiring loss. As an integrated module of antenna and circuit board that incorporates these technologies, compared to separate configurations of antenna and control circuit, it can ensure feeding characteristics, thus eliminating the need for antenna design, layout design, and feeding characteristic evaluation for product evaluation. This will significantly shorten the development cycle and design burden of circuit board modifications, and can easily realize the wireless power supply function.

Figure 2. Comparison of Development Processes

This product uses the 13.56MHz high frequency magnetic resonance method, which allows for smaller antenna sizes, thus integrating the antenna, matching circuit, and wireless charging IC onto a small circuit board, which is difficult to achieve with existing wireless power supply standards. In terms of size, the transmitter module “BP3621” measures 35.0mm×26.0mm×1.5mm, while the receiver module “BP3622” measures 24.0mm×17.0mm×1.5mm. Additionally, all required components are mounted on the front, and by adopting a fully flat circuit board structure on the back, it becomes easier to adhere to the shell, which helps simplify the shell structure and improve design flexibility.

Figure 3. Product Size and Appearance

Since this product uses the same 13.56MHz high frequency band as the NFC communication standard, the built-in antenna of the module can support both power supply and communication functions simultaneously. It supports bidirectional data communication (communication speed of 212kbps, up to 256 bytes) and NFC Forum Type3 Tag communication, which helps expand the data communication functions of application products, such as secure transmission and rewriting of sensor data, device information, and authentication information, firmware downloads, and sending battery output voltage values.

Figure 4. Wireless Data Communication Schematic

To enhance convenience and achieve waterproof and dustproof functions, the industry has been researching the integration of wireless charging modules into various application devices. For computer keyboards, which are gradually becoming standard with wireless connections, this can be considered a good application case, as it eliminates the hassle of changing batteries and connecting for charging via data cables. By supplying power from a tablet with an integrated power supply module to a mobile keyboard with an integrated power receiving module, a completely wireless keyboard can be realized without the need for battery replacement or charging.

Figure 5. Application Case

This product is also suitable for devices that require waterproof and dustproof features, such as electronic shelf labels and GPS trackers. The weight of the power receiving module is only 0.38g, so in certain cases, by installing the wireless charging module, smaller capacity batteries can be used, helping to reduce the weight of electronic devices. It is expected that this product will expand its applications to more cases in the future.

ROHM has published application guidelines on its official website, committed to further assisting customers in easily achieving wireless charging functions and shortening development cycles. The application guidelines provide the setup conditions for the main functions of power supply and communication, as well as connection methods. In the future, ROHM also plans to expand its lineup of evaluation boards and other products to further strengthen its support system and promote the popularization of wireless charging modules.

Figure 6. Application Guidelines

In the future, ROHM will continue to expand its lineup of compact and high-output wireless charging modules, further expand application fields, and increase the range of applicable target devices, contributing to reducing customers’ design and development cycles and enhancing the convenience of application products.

Figure 7. Product Lineup