Application Note
P9261
-3C-CRBv2
Power
-Loss and FOD Tuning Guide
R16AN0023EU0100 Rev.1.00
May 2, 2022
Page 1
© 2022 Renesas Electronics
This application note describes the functionality of the P9261 Automotive CRB 2.0 Wireless Power Transmitter
(Tx) and its Foreign Objects Detection (FOD) by measuring the power that is being absorbed by the object.
Contents
1. Introduction ................................................................................................................................................... 1
2. P9261 Power-Loss FOD Tuning Overview .................................................................................................. 2
3. Step-by-Step Power-Loss FOD Thresholds Tuning................................................................................... 3
4. P9261 Power-Loss FOD Applicable Registers ........................................................................................... 6
5. Revision History ........................................................................................................................................... 6
1. Introduction
The P9261 Automotive CRB 2.0 Wireless Power Transmitter (Tx) is used to transmit wireless power to wireless
power receivers (Rx) devices following WPC specifications and protocols. An important operating attribute of all
WPC systems is the ability to detect Foreign Objects (FO) by measuring the power that is being absorbed by the
object. In standard operating mode, the Rx device will send a Received Power Packet (RPP) approximately
every 500ms. The RPP informs the Tx how much power the Rx is currently receiving and includes the estimate
of the power loss in the Rx device due to friendly metal energy absorption. Once the RPP is received, the Tx
compares this power to the Tx
POWER
(see Equation 1) and if three consecutive results of PDiff (see Equation 2)
are above the PThreshold, then the Tx will shut down due to FOD alarm.
Tx
POWER
= VBRG
(
mV
)
x IBRG
(
mA
)
/1000
Equation 1
where,
VBRG = input voltage to the Tx controller IC (measured at VBRG_IN (pin 40) of the P9261)
IBRG = DC average current in the Tx Full Bridge (measured across RSNS (R18) on P9261 EVK)
The VBRG and IBRG values are directly measured by the P9261 during operation and the values that need to
be tuned are the various power loss levels due to friendly metal associated with the Tx device under design at
the various power levels. The P9261 FOD tuning includes tuning the Tx losses out of the equation used to
determine if a FO is present or not. The Renesas solution uses regions with gain and offset to change the
threshold based on the latest value of the RPP packets received. If RPP is larger than Tx
POWER
, PDiff will be
treated as 0.
PDiff = Tx
POWER
− RPP
Equation 2
After PDiff is calculated, the P9261 calculates the thresholds used to determine if FOs are present or if normal
power transfer can continue safely. The thresholds can be calculated using the following formulas and the value
of the threshold is dependent upon the most recently received RPP value:
FOD Pthreshold = (PRX*Gain
REGION
+ FOD_Offset
REGION
) + Offset_FOD
Equation 3
P9261-3C-CRBv2 Power-Loss and FOD Tuning Guide
R16AN0023EU0100 Rev.1.00
May 2, 2022
Page 2
Once the FOD power thresholds are calculated, they ar e compared to the calculated P
DIFF
result and the result is
used based on the following FW code snippet:
If PDIFF > PThreshold
{
Count_FOD++
IF Count_FOD > 3
{
FOD Shutdown
}
}
Else
{
Count_FOD = 0
}
2. P9261 Power-Loss FOD Tuning Overview
This section describes how to tune the P9261 Power Loss FOD using the registers available for this purpose.
Figure 1. P92 6 1 Automotiv e CRB 2.0 G UI S c reen Ca pt ure FOD Tunin g Tab