The new wireless charging solution consists of a power receiver integrated circuit (RAA457100) and a power transmitter integrated circuit (RAA458100). Each IC includes all the functions necessary for wireless charging on a single chip. Renesas will also offer an evaluation kit to assist manufacturers with their wireless charging designs.
Wireless charging technology eliminates the need to change batteries or connect a power cable. This convenience is highly appealing for a variety of applications, such as smartphones and wearable devices. Wireless charging technology is of particular interest in low-power applications, such as hearing aids that require small form factors, as well as water and dust resistance. However, existing wireless charging technologies have been deemed unsuitable for systems that use secondary lithium-ion (Li-ion) batteries for these low-power applications. This is due to the challenges of achieving smaller form factors with antenna sizes dictated by current standards, and the heat dissipation caused by the large charging currents required for low-power applications.
With its new wireless charging solution, Renesas has combined its expertise in wireless charging systems with its microcontrollers (MCUs) to ensure all key system components are housed in a compact package, simplifying design.
Key features of the RAA457100 power receiver IC include:
1) Enabling more compact devices by integrating all necessary wireless charging functions into a 3.22 mm x 2.77 mm package.
The power receiver IC incorporates a synchronous rectifier circuit that converts the AC power used to drive the power receiver's antenna coil into DC, and a charging control circuit for charging a secondary lithium-ion (Li-ion) battery. A 12-bit analog-to-digital converter (ADC) monitors the battery voltage and current during charging, providing this information to the power transmitter to maintain optimal charging power levels. The IC also includes protection features for the secondary Li-ion battery and a DC/DC regulator, all on a single chip.
2) On-chip DC/DC converter with 85 percent efficiency for extended battery operation.
Low-power applications, such as portable devices and hearing aids, typically use compact batteries with small capacities, making efficiency crucial. The integrated DC/DC converter achieves high efficiency when the system is operating at a low load level of around 1 mA, enabling longer battery life.
Key features of the RAA458100 power transmitter IC:
3) Integration of all circuitry necessary for wireless power transmission and support for a 5V supply voltage from mobile batteries.
Generally, contactless power transmission involves applying a 125 kHz alternating current to the power transmitter's antenna coil to excite the power receiver's antenna coil and generate AC power. Renesas' new power transmitter drives a bridge circuit and controls the alternating current to obtain the transmission power value required by the power receiver. The power transmitter IC integrates bridge circuit overcurrent protection and two-line external overheat protection. System builders can modify parameter values by programming the readout registers with external EEPROM data via an I2C interface to meet their application requirements. The solution can be further customized by connecting an external MCU.
The Renesas μPA2690T1R power MOSFET is recommended for the bridge circuit configuration. When combined with the RAA458100, the system builder can choose between half-bridge and full-bridge configurations to match the power level of the power transmitter.
Availability:
Samples of the new wireless charging system solution will be available in November 2016. (Availability is subject to change.)
