REVISION 08/26/15
3
P9025AC FOD TUNING GUIDE
AN-886
Once the FOD1 trim settings are determined and FOD2 offset is incorporated, the reported power by the Rx (Rx
POWER_FOD
) is
now a total power value as opposed to just the power delivered to the load. This will allow the FOD calculation to be accurate
based on the operating power levels of the Tx module and the Rx module when no foreign objects are present.
where,
-350mW < FOD
PDIFF
< 0mW for 0 to 1A load levels
Pre-programmed Banks (FOD1)
The P9025AC device is pre-programmed with FOD default curves in an effort to expedite and simplify development of wireless
charging systems. These allow end-users the option of using a resistor to select the FOD curve that mostly closely matches the
end product. IDT derived these particular curves based on existing systems with a variety of permeable materials near the Tx
and Rx coils. The following curves are the default values stored in the FOD banks of the P9025AC-RNDGI device (refer to the
P9025-R-EVK FOD Calculator.xlsx for exact values).
The Rx Reported Received Power vs. Load Current graph is an indication of the power lost due to the electrical operations
required for the Tx and Rx to function as the load current changes. As you can see, the reported Power received is approximately
1W when no external load is applied and can exceed 7W when 5W is delivered to the load.
Figure 1. P9025AC-R Default FOD1 Curves Banks 1- 7, 10
(Maxes out power reported to essentially disable
FOD)
. Banks 8 and 9 are Reserved for Custom Trimming to be Performed by an FOD Expert using
Specialized Equipment.
In order to program the P9025AC to properly account for losses due to foreign objects, the Rx Reported Received Power vs.
Load Current curves must be understood. These curves display the transmitted power of the Tx including the power delivered
to the load. The Tx device will monitor the power level that it is consuming (by measuring the RMS input current and DC input
voltage), then compare this result to the reported received power level (the point on each curve based on selected bank). In order
to be WPC-compliant, the Tx measured power can be equal to or less than up to 350 mW less than the Rx reported received
power across the load spectrum.
