P9222-R/RN Datasheet

© 2019-2022 Renesas Electronics Corporation

27

May 5, 2022

7. WPC Mode Characteristics

For a description of the startup process for wireless charging, which is compliant with the WPC protocol, see “Startup”.

7.1 WPC-Compliant Power Transfer

Once the “identification and configuration” phase is completed, the transmitter initiates the power transfer phase. The P9222-R/RN control

circuit measures the rectifier voltage and sends CEPs to the transmitter to adjust the rectifier voltage to the level required to maximize the

efficiency of the linear regulator and to notify the Tx of the current Received Power Packet for foreign object detection (FOD) in order to

guarantee safe, efficient power transfer. The P9222-R/RN is compatible with WPC specification and can use compatible Rx coils. Each receiver

coil type has a unique inductance value. As such, a unique resonant capacitor (CS) is used for a given type of receiver coil.

7.2 Advanced Foreign-Object Detection (FOD) in WPC Mode

When metallic objects are exposed to an alternating magnetic field, eddy currents cause such objects to heat up. Examples of parasitic metal

objects are coins, keys, paperclips, etc. The amount of heating depends on the amplitude and frequency of the magnetic field coupled, as well

as the characteristics of the object, such as its resistivity, size, and shape. In a wireless power transfer system, the heating manifests itself as

a power loss, and therefore a reduced power transfer efficiency. Moreover, if no appropriate measures are taken, the heating could lead to

unsafe situations if the objects reach high temperatures.

WPC power transmitters and receivers need to also compensate for the power loss due to parasitic metals intentionally designed into the final

product; i.e., metals that are neither part of the power transmitter nor of the power receiver, but which absorb power from magnetic field coupling

during the power transfer, such as Li-ion batteries, metallic cases, etc.

The P9222-R/RN uses advanced FOD techniques to detect foreign objects placed on or near the transmitter base station. The FOD algorithm

includes values that are programmable through either the I2C interface or external EEPROM memory bits. Programmability is necessary so

that the FOD settings can be optimized to match the power transfer characteristics of each particular WPC system to include the power losses

of the Tx and Rx coils, battery, shielding, and case materials under no load to full load conditions. The values are based on the comparison of

the received power against a reference power curve so that any foreign object can be sensed when the received power is different from the

expected system power.

The P9222-R/RN FOD values need to be tuned prior to production for WPC compliance using final production hardware and coils.

7.3 WPC Modulation/Communication

The P9222-R/RN operates in the WPC mode using a single LC tank Rx coil and requires AC modulation capacitor connections for WPC

communication. The capacitors CM1 and CM2 (connected to pins CM1 and CM2 respectively; see Figure 21) and the LC tank accomplish WPC

modulation. The capacitor values should be tuned to achieve maximum efficiency while still providing adequate communications.

Figure 21. Rx Modulation Components

AC1

AC2

CMA

CM2

LDO VOUT

CMA

CM2

VRECT

CM1

CM1

CMB

CMB