Contactless wireless charging for healthcare and wearables

September 27, 2016 // By Graham Prophet
Renesas has added a single-chip offering that combines all the functions needed for wireless charging for low-power applications, such as hearing aids and other wearable devices that require resistance to water and dust.

A power receiver integrated circuit (RAA457100) and a power transmitter IC (RAA458100) come with an evaluation kit to help manufacturers with their wireless charging designs. Wireless charging, Renesas notes, 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 for these low-power applications, in part due to difficulties in achieving smaller form factors with the antenna size mandated by the current standards; and heat dispersion due to large charging currents that are required to charge low-power applications.


Renesas says it has combined wireless charging with its microcontrollers to enable all key system components in a small space for easier design implementation. The RAA457100 Power Receiver IC, in a 3.22 x 2.77 mm package, incorporates a synchronous rectifier circuit that rectifies the AC power used to excite the antenna coil of the power receiver 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 the single chip. An on-chip DC/DC converter with efficiency of 85% at 1 mA gives extended operation on battery power

The RAA458100 Power Transmitter IC includes all circuits needed for wireless power transmission and support for single 5V power supply voltage from mobile batteries. Power transmission involves applying a 125 kHz alternating current to the antenna coil of the power transmitter to excite the antenna coil of the power receiver and generate AC power. Renesas’ power transmitter IC drives a bridge circuit and controls the alternating current to obtain the transmission power value required by the