WCT1012VLF/WCT1013VLH Consumer MP-A11 (WCT-
15W1CFFPD) V1.0 Wireless Charging Application User’s
Guide, Rev. 1, 05/2019
NXP Semiconductors
13
The reference Q factor is defined as the Q factor of the test power transmitter #MP1’s primary coil at the
operating frequency of 100 kHz with RX positioned on the interface surface and no FO nearby. Due to
the differences between its design and that of the test power transmitter #MP1, the TX needs to convert
the Q factor it measured to that of the test power transmitter #MP1. NXP provides the conversion
method and must get the on-board parameters first. The TX performs the automatic calibration and gets
the parameters at the first powerup after a new image is flashed. These parameters are then written to the
flash memory. Therefore, it is necessary to ensure that there is no object on the TX surface during the
first powerup after flashing a new image.
Figure 10. Q factor threshold example
Free-resonance Q factor
The free-resonance Q factor detection detects the decay rate of the resonance signal, as shown in
Figure
11
. With the system’s high Q, just a few pulses near the resonant frequency are sufficient to serve as
impulses and start the system ringing. Collect the ADC data of the tank voltage (or coil current), and get
the decay rate of the signal.
Q=
𝜋
/(-ln(Rate))
Rate is the value of the decay rate of the resonance signal.