Infineon AN234970, Manual, Page: 9 / 36

Application Note 9 of 36 002-34970 Rev. **
2022-05-03
Foreign object detection tuning guide for wireless power transmitters
Applicable for WLC ICs
Getting started
Case 1 represents the region 1 and Case 2 represents the region 2 in Figure 4 .
FO Threshold
Threshold_max
1
2
Rec
ei
ve
r
w
ith
ou
t F
O
FO present with high power dissipation in FO.
FO detected.
Re
ce
iv
er
w
ith
F
O
2
Re
ce
iv
er
w
ith
F
O1
Figure 4
FOD mechanism based on system power loss
The thresholds for FOD can be configured. Refer to Section 3.6 for tuning thresholds for power loss-based FOD.
2.1.3 FOD using pre- and in-power transfer methods
Figure 5 illustrates the free-air Q factor FOD mechanism. The object detection mechanism identifies the
placement of an object and initiates the Qi communication stack, which involves pre- and in-power transfer
FOD mechanisms. Pre-power transfer data is measured by Tx during the analog pings. Upon object detection,
the free-air FOD method finds FOs. If the device is a valid receiver, it proceeds to the identification and
configuration phases. The FOD/qf packet is exchanged for an EPP device optimizing the FOD for EPP devices.
The WLC
’s patented Q factor-based FOD mechanism identifies the FOs already present or while entering the
interface field before power transfer starts
A power loss-based FOD mechanism identifies FOs, which may enter the interface surface after power transfer.
The WLC power transmitter uses a combination of both Q factor and power loss-based mechanisms for optimal
and efficient FOD in BPP and EPP devices. Refer to the user manual for UI indication for FOD.