Batteries and Portable Power

Misalignment Detection in Wireless Power Receiver Ensures High-Efficiency

ROHM Semiconductor has recently announced the development of a wireless power receiver IC designed to charge smartphones and other portable devices. The BD57011GWL is compliant with WPC’s (Wireless Power Consortium) latest Qi Low Power Ver1.1 standard for wireless power transmission and features low heat generation in a monolithic design, reducing temperature rise by up to 75% during wireless charging. This provides a balance between mounting area and heat generation. In addition, the industry’s first misalignment detection function detects incorrect positioning of the target device on the charging pad, which can lead to decreased charging efficiency.

Wireless power transmission technology eliminates the need for a power cord for charging portable devices, is expected to improve the waterproof and dustproof properties of device connectors, and supports a variety of terminals with a single wireless charger. However, a major challenge with 5W-class wireless power transmission for smartphones and other portable equipment is the relatively large amount of heat generated during charging.

The new device claims the industry's first misalignment detection function improves charging efficiency. During charging, incorrectly positioning the target device on the charging pad may cause a significant drop in charging efficiency. To prevent this, ROHM has included a misalignment detection function that triggers an alarm, allowing the user to reposition the device to achieve maximum charging efficiency.

The BD57011GWL also features low heat generation in a monolithic (single-chip) design. Cutting-edge BiC-DMOS processes are utilized for the lowest MOSFET ON resistance possible. This, along with an optimized monolithic design, provide an ideal balance of small mounting area with low heat generation, reducing temperature rise during wireless power charging by approximately 75% compared with conventional solutions.

WPC Qi Low Power Ver1.1 Standard is the latest international wireless power transmission standard, Qi Low Power Ver1.1, and was established by WPC in April of 2012. The difference between this latest standard and Low Power Ver1.0, established in 2010, is that Ver1.1 includes the requirement for a built-in FOD (Foreign Object Detection) function to improve safety. ROHM has joined as a full member of WPC, which is comprised of a maximum of 25 companies, and plays an active role as a consultant as well as in the development of the increasingly popular Qi wireless power transmission standard.

FOD (Foreign Object Detection) provides a greater level of safety; FOD is required in the latest Qi standard in order to prevent chassis deformation and/or burns due to excessive heat generation of a foreign metallic object when placed between the transmitter and receiver, dramatically improving safety. FOD involves complex calibration of the receiver and transmitter, achieved in this case by combining ROHM's renowned analog technology together with ROHM Group LAPIS Semiconductor's industry-proven digital expertise. And, since the power loss is calculated at the receiving end, the different loss error for each receiver can be fine-tuned via external resistor, ensuring flexible, high-precision FOD operation.

ROHM Semiconductor
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