Is there a way to program MAX77950 registers default settings in the OTP so that it can be used without a microcontroller?

Please note that OTP settings can only be done in the factory. V olumes needs to be very high for us to do this OTP change, and needs a strong business justification.

Can the Thermal Protection parameters be modified on the MAX77950?

No, the Thermal Protection parameters on the MAX77950 cannot be modified. These are fixed thresholds built-in to the chip for thermal protection.

What's the relationship between the Thermal Protection parameters (TJOFF, TJWARN) and the Die temperature on the MAX77950?

These are fixed thresholds built-in to the chip for thermal protection. The present chip temperature (die temperature) is tracked in the TDIE_VALUE register, which is updated periodically during chip operation. TJOFF (165degC) - Beyond this temperature the chip will shut down to prevent chip failure. TJWARN (120degC) - At this temperature the chip will warn the user that it is operating at a temperature higher than typical operating temperatures. Based on this the user can configure the chip, for example, stop charging or reduce charging current.

What is the recommended process for finding the foreign object detection (FOD) coefficients to set the register values for the MAX77950 wireless power receiver?

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

Why MAX77950 fails to communicate with QI charger, When Vrect is powered externally?

Vrect should have ripple for proper communication. An external power supply, especially with large output capacitance, will mute this ripple and interfere with communication.

Can MAX77950 be powered through Vrect or Vout pins?

Yes, MAX77950 can be powered by connecting a source to VRECT or VOUT.

What would be the expected quiescent current when the MAX77950 is on standby i.e. wireless receiving/rectification is not happening and the target device is working in battery operated mode?

The typical supply current would be 5mA (typ). However, with this wireless chip, the typical setup involves external FET-based connection/disconnection of the IC with the battery when wireless charging is needed/not needed. Once a wireless power transmitter is detected, the MAX77950 would alert the MCU of TX’s presence, and the MCU must subsequently connect the MAX77950 output with a DC-DC converter charging IC.

Which Tx is recommended for MAX77950 evaluation

The following transmitters are good for MAX77950 evaluation: A11 and PMA7.

Is MAX77950 PeerPower mode compatible with Qi?

The MAX77950 PeerPower mode is not compatible with Qi, although it is similar to Qi, with the following exceptions: No FOD support Only Proportional parameter used for frequency control among PID (Proportional/Integral/Derivative)

Can MAX77950 work as transmitter?

MAX77950 can work as TX. MAX77950(TX) + MAX77950(RX) should work in PeerPower mode only. On the EVkit, we can get about 1.5W with 5V in and we can get >5W with 6V input. The limit is usually the overcurrent event on the transmit side will turn off output power. Setting the current limit high or limiting the power on the receiver will keep it in a functional state.