P9221-R Datasheet

© 2017 Integrated Device Technology, Inc.

18

April 4, 2017

8.10 Alignment Guide – ALIGNX and ALIGNY

This feature is used to provide directional information regarding the transmit coil and receive coil alignment while the wireless charger is in

normal operation mode. Sensing coils (see the basic application circuit on the first page) are placed on the wireless power receiver side between

the power RX coil and power TX coil. Special design enables the sensing coils to output zero voltage when the alignment is optimum while

misalignment between the transmitter and receiver coils will result in a voltage on the sensing coils. These signals are internally rectified, filtered,

and passed through the ADC providing quantitative information on the amount of misalignment. The higher the signal is, the more the coils are

misaligned.

Furthermore, the signal magnitude on ALIGNX and ALIGNY provides directional information by measuring the phase between the input power

AC signal and horizontal and vertical alignment signals. Once the signal passes through the ADC, the alignment information is represented by

22 respectively, which indicate the misalignment direction and magnitude.

The application processor can provide 2D visual graphics that suggest how much the power coils are misaligned in each direction and can

suggest that the user move the device on the TX pad for the best alignment to improve the power transferred and reduce the charging time.

8.11 Received Power Packet Offset and Gain Calibration – RPPO and RPPG

The received power packet offset (RPPO) and received power packet gain (RPPG) calibrations have dedicated pins for tuning foreign object

detection (FOD). The offset calibration can be tuned by the voltage level of RPPO to a value between 0.1V to 2.1V, which corresponds to a

power offset range of 1.54W to 2.34W. The gain can be modified by setting the voltage level of the RPPG pin. The range of the control gain is

from 0.122 to 2.33 where the level is determined by a ratiometric voltage in the range of 0.1V to 2.1V on the RPPG pin.

To disable the FOD, the voltage on both RPPO and RPPG must be set to 0.1V. Neither pin should be floating. If FOD is not required, the RPPG

and RPPO must be set to 0.9V, which defaults to gain = 1 and offset = 0.

8.12 Advanced Foreign Object Detection (FOD)

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 on 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 undesirable temperature.

During the power transfer phase, the receiver periodically will communicate to the transmitter the amount of power received by means of a

received power packet. 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 for and compensate for all

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

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

in Table 7.

interface surface.