P9222-R/RN Datasheet

© 2019-2022 Renesas Electronics Corporation

39

May 5, 2022

9.3

Overvoltage (OV) Protection Configuration

The wireless charging receivers are vulnerable to external high voltage condition (> 20V) caused by coupling factor changes or other abnormal

behavior of rogue wireless power transmitters. The overvoltage protection function should be carefully configured to protect the receiver from

worst cases. The overvoltage protection limit sets the maximum allowable Vrect voltage. If Vrect reaches the voltage limit (default OV voltage

is 15V), the P9222-R/RN will do the following:

1.

Turn on the internal clamping circuit

2.

Enable an additional DC load when Vrect reaches 90% of the set level

3.

Send an End Power Transfer packet (OV) to TX

The default OV protection limit value can be configured by writing a configuration file into the external EEPROM. The configuration file can be

generated using the P9222-R/RN Windows GUI. For information on how the configuration file can be generated using the P9222-R/RN Windows

GUI, see “VOUT Configuration Change Using an External EEPROM.”

In addition, an external AP can adjust overvoltage protection limit by writing to the OV Set register (0x4C) via the I2C interface.

9.4

FOD (Foreign Object Detection)

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

metal objects are coins, keys, paper clips, etc. The amount of heating depends on the strength of the coupled magnetic field, 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 reduction in power-transfer efficiency. Moreover, if no appropriate measures are taken, the heating could be sufficient that

the foreign object could become heated to an unsafe temperature.

During the power transfer phase (see Power Transfer), the receiver periodically communicates to the transmitter the amount of power received

by means of a Received Power Packet (RPP). The transmitter will compare this power with the amount of power transmitted during the same

time period. If there is a significant unexplained loss of power, then the transmitter will shut off power delivery because a possible foreign object

might be absorbing too much energy.

For a WPC system to perform this function with sufficient accuracy, both the transmitter and receiver must account and compensate for all of

their known losses. Such losses, for example, could be due to resistive losses or nearby metals that are part of the transmitter or receiver.

Because the system accurately measures its power and accounts for all known losses, it can thereby detect foreign objects because they cause

an unknown loss. The WPC specification requires that a power receiver must report to the power transmitter its received power (PPR) in an

RPP. The maximum value of the received power accuracy

������������ΔdependsonthemaximumpowerofthepowerreceiverasdefinedinTable10.

The power receiver must determine its PPR with an accuracy of ±

������������Δ,andreportitsreceivedpowerasPRECEIVED=PPR+������������Δ.Thismeans

that the reported received power is always greater than or equal to the transmitted power (PPT) if there is no foreign object (FO) present on the

interface surface.

Table 10. Recommended Maximum Estimated Power Loss

Maximum Power (W)

Maximum

������������Δ(mW)

5

350

The compensation algorithm includes values that are programmable via either the I2C interface or OTP bits. Programmability is necessary so

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

losses of the transmit and receive 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 than the expected system power.