Application Note
7 of 36
002-34970 Rev. **
2022-05-03
Foreign object detection tuning guide for wireless power transmitters
Applicable for WLC ICs
Getting started
Where F
res
is the reported RF, F
scaled
is the scaled RF, F
threshold
is the threshold RF. Threshold_percent and
ScalingFactor are configurable from the Wireless Charging Configuration Utility.
Te
st
R
ec
ei
ve
r
w
ith
F
O
1
Te
st
R
ec
ei
ve
r
w
ith
F
O
2
Te
st
R
ec
ei
ve
r1
w
ith
ou
t F
O
Te
st
R
ec
ei
ve
r2
w
ith
ou
t F
O
Scaled RF
FO present
FO present
NO FO
Higher
threshold of RF
Lower
threshold of RF
Figure 2
Resonance frequency-based FOD
The FO is detected if the difference between measured and scaled reference resonance frequency is greater
than the threshold. “ScalingFactor” and “Threshold_percent” are configurable from the wireless charging
configuration utility.
In case of a FOD, the Tx responds to the FOD/rf or FOD/qf packets with a NAK packet leading to immediate
power disconnect. The communication is re-established only after the object is removed. Refer to the user
manual for LED user interface for FO detection.
2.1.2
FOD during power transfer
The power loss FOD mechanism involves measuring the transmitter power periodically during power transfer
and comparing the measured power with the loss curve estimates given by the receiver. To improve the
reliability and accuracy of FOD, additional methods are introduced by the WLC power transmitter.