P9412 Datasheet

R35DS0011EU0120 Rev.1.2

Jul.6.21

Page 17

the efficiency of the main LDO linear regulator, and to notify the Tx of the current Rectified Power Packet for

Foreign Object Detection (FOD) to guarantee safe efficient power transfer. The P9412 is compatible with WPC

(latest specification) and can use compatible Rx or TRx coils. Each receiver coil type has a unique inductance

value. As such, a unique resonant capacitance (CS) may be needed to optimize performance when connected to

a given type of receiver coil.

3.13.3.

Advanced Foreign Object Detection (FOD) 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 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 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 power transfer, such as Li-ion

batteries, metallic cases, etc.

The P9412 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 MTP 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 than the expected system power.

The P9412 FOD values need to be tuned prior to production for WPC compliance using final production

hardware and coils.

3.13.4.

Status/Interrupt Output

When the power transfer connection is established and stable, the VOUT MLDO is enabled. The /INT (GPOD3)

should be connected to the AP so that the P9412 can send interrupts to the AP and allow the AP to perform

status and interrupt command checks periodically during power transfer. Additional connections from the P9412

to the host AP are recommended as shown in the reference schematic (PDET, SW_Inhibit, and CPout_GD as

examples).

3.13.5.

WPC Modulation/Communication

The P9412 operates in WPC mode using a single LC tank Rx coil and requires AC modulation capacitor

connections for WPC communication. The LC tank should be tuned to achieve maximum efficiency (CMA, CMB,

CM1, CM2 connected to pins CMA, CMB COM1, COM2) in order to accomplish WPC modulation.