How to make wireless charging more pervasive?

Proprietary power extensions with Qi backward compatibility

In the highly competitive inductive wireless charging market, OEMs have a continuous desire for differentiated features and enhanced user experience. This has led to the emergence of proprietary fast-charging protocols that coexist with the Qi standard.

For example, the WPC protocol provisions for proprietary power delivery extensions (PPDEs) enable manufacturers to extend their solutions’ capabilities. In addition, several smartphone OEMs offer proprietary high-power inductive wireless charging up to 50 W, limited by regional spectrum regulations. As the Qi standard continues to evolve and may offer fast charging with increased power capability in the future, product manufacturers look for flexible, programmable solutions that can be software upgraded, maintained, and offer an enhanced user experience over the product’s lifetime.

A wireless transmitter controller

An example of an IC to that addresses some of these expressed requirements for OEMs is the WLC1115 transmitter controller, which is compliant with the latest Qi and USB-C PD specifications and features integrated gate drivers for buck and inverter power stage MOSFETs. We’ll use this as an example to highlight how these requirements can be met.

An integrated buck controller generates the required bridge voltage to power the full-bridge inverter, which, supplies the power transmitter LC tank to deliver power to the power receiver. The buck converter supports an input voltage range of 4.5 V to 24 V. The controller’s integrated gate drivers are designed to control a full-bridge or half-bridge inverter depending on the Qi specification type and the operating scenario. Figure 1 shows the MP-A11 coil-based transmitter system that uses the fixed-frequency variable-input voltage control for the inverter stage.

A transmitter designed with the transmitter controller IC can offer several benefits to the power stage. In addition to a programmable switching frequency range up to 600 kHz, there is flexibility to dynamically change input voltage from 5 V to 20 V with PD input. This helps achieve better efficiency with a USB-PD type input since the input voltage can be dynamically configured to keep the buck stage input close to the output, optimizing efficiency. Peak 15 W efficiency measured from 15 V PTx input to 12 V PRx output is greater than 83 percent. In addition, standby power can be reduced by operating at 5 V in idle mode. This is typically about 67 mW but it can be further reduced below 25 mW with system-specific firmware enhancements.

Protection for the buck stage includes under voltage protection (UVP) and over voltage protection (OVP) on both the input and output as well as over current protection (OCP) and short circuit protection (SCP) on the output and protections specific to the PD (for example V_BUS to CC short).

Foreign object detection

To meet the Qi v1.3.2 standard, the transmitter controller supports enhanced foreign object detection. This includes FOD based on Q factor, resonance frequency, power loss, and over temperature protection (OTP) (if a thermistor is used).

The Q factor and resonance frequency measurements are used for FOD before the power delivery phase. The PRx reports the Q factor and resonance frequency reference values calibrated with a Qi-defined reference coil. The PTx compares the reported values to its measured values in situ to determine the presence of a foreign object. A scaling factor is used to convert the PRx-reported Q factor and resonance frequency values to those equivalent to the reference transmitter coil and to accommodate measurement variations.

To prevent erroneous disconnects and improve user experience, the controller uses an adaptive algorithm that distinguishes between real P_loss FOD vs. P_loss arising from poorly-coupled PRx. The FOD coefficients and the P_loss thresholds are fully configurable to adapt to the system design.