The BQ51013C integrates a fully compliant WPC v2.0 communication algorithm in order to streamline receiver designs (no extra software development required). Other unique algorithms such as Dynamic Rectifier Control are also integrated to provide best-in-class system performance. This section provides a high level overview of these features by illustrating the wireless power transfer flow diagram from start-up to active operation.

During start-up operation, the wireless power receiver must comply with proper handshaking to be granted a power contract from the TX. The TX will initiate the handshake by providing an extended digital ping. If an RX is present on the TX surface, the RX will then provide the signal strength, configuration and identification packets to the TX (see volume 1 of the WPC specification for details on each packet). These are the first three packets sent to the TX. The only exception is if there is a true shutdown condition on the EN1/EN2, AD, or TS/CTRL pins where the RX will shut down the TX immediately. See Table 8-4 for details. Once the TX has successfully received the signal strength, configuration and identification packets, the RX will be granted a power contract and is then allowed to control the operating point of the power transfer. With the use of the BQ51013C Dynamic Rectifier Control algorithm, the RX will inform the TX to adjust the rectifier voltage above 7 V prior to enabling the output supply. This method enhances the transient performance during system start-up. See Figure 8-2 for the start-up flow diagram details.

Figure 8-2 Wireless Power Start-Up Flow Diagram

Once the start-up procedure has been established, the RX enters the active power transfer stage. This is considered the “main loop” of operation. The Dynamic Rectifier Control algorithm determines the rectifier voltage target based on a percentage of the maximum output current level setting (set by K_IMAX and the ILIM resistance to GND). The RX sends control error packets in order to converge on these targets. As the output current changes, the rectifier voltage target will dynamically change. The feedback loop of the WPC system is relatively slow where it can take up to 90 ms to converge on a new rectifier voltage target. It should be understood that the instantaneous transient response of the system is open loop and dependent on the RX coil output impedance at that operating point. More details on this is covered in the section Receiver Coil Load-Line Analysis. The “main loop” also determines if any conditions in Table 8-4 are true in order to discontinue power transfer. See Figure 8-3 which illustrates the active power transfer loop.

Figure 8-3 Active Power Transfer Flow Diagram

Another requirement of the WPC v2.0 specification is to send the measured received power. This task is enabled on the device by measuring the voltage on the FOD pin which is proportional to the output current and can be scaled based on the choice of the resistor to ground on the FOD pin.