We recommend the following process:
- Decide the Max output Power and turn off the FOD feature at the Tx device.
- We recommend 7.5W, as assuming 75% efficiency, 7.5W/.75 = 10W, which can be reported by the received power packet (RPP)
- Decide the output voltage
- We recommend 7.5V, so VOUTSET[6:0] to 0x4B (=7.5V)
- Write all VRECT_TARGET_Yn registers to 0x81. This makes VRECT 7.59V regardless of the load. Don’t change VRECT_TARGET_Xn and VRECT_TARGET_PMA_Yn
- We don’t recommend to changing VRECT_ADJ
- Set load current equal to X0 (using FOD_Xn and Xn equations in datasheet) and measure TX power at the Tx input
- Calculate Y0 (Rx Power) as Tx power + 175mW, and determine FOD_Y0 using the datasheet equation.
- This makes Tx power - Rx power = -175mW
- Write the FOD_Y0 value via I2C, then turn on the FOD feature at the Tx device to ensure Tx doesn't terminate power transfer.
- If there is no termination of power, then turn of FOD again and move to the next point (X1)
- Repeat to get FOD_Yn for all 16 values of Xn
After all values are written, enable the FOD feature and step the load from min to max to ensure the Tx doesn't terminate power. Make sure the step is slow, since the control loop between Tx and Rx is very slow. In the WPC spec, the RPP reporting interval is 1.5s