Wireless charging chips aim at wearables

September 27, 2016 // By Nick Flaherty
Renesas Electronics (Tokyo, Japan) has launched single chips for wireless charging in low-power applications such as hearing aids and other wearable devices that require resistance to water and dust.

The new wireless charging solution consists of a power receiver integrated circuit (IC) (RAA457100) and a power transmitter IC (RAA458100). Each IC includes all functions needed for wireless charging on a single chip. Renesas will also offer an evaluation kit to help manufacturers with wireless charging designs.

Wireless charging is of particular interest in low-power applications such as hearing aids that require small form factors as well as resistance to water and dust. However, existing wireless charging technologies have been considered unsuitable for charging systems employing compact lithium-ion (Li-ion) secondary batteries through the challenge of achieving smaller form factors with the antenna size mandated by the current standards and the heat dissipation from the large charging currents that are required to charge low-power applications.

With the new wireless charging solution, Renesas has combined its wireless charging system expertise with its microcontrollers (MCUs) to enable all key system components in a small space for easier design implementation.

The RAA457100 Power Receiver IC combines all the charging functions needed for wireless charging in a 3.22mm x 2.77mm package. This includes a synchronous rectifier circuit that rectifies the AC power used to excite the antenna coil of the power receiver into direct current, and a charging control circuit for charging a lithium (Li-ion) secondary battery.

A 12-bit A/D converter is used to monitor the battery voltage and current during charging, and this data is supplied to the power transmitter to maintain the optimal charging power level. Protection features for the Li-ion secondary battery and a DC/DC regulator are also incorporated on a single chip. An integrated DC/DC converter itself achieves industry-leading high efficiency of 85 percent when the system is operating at a low load level of around 1 mA, which enables longer battery life.