9.2.1.2.1 Using the bq51003 as a Wireless Power Supply

Figure 32 is the schematic of a system which uses the bq51003 as a power supply.

When the system shown in Figure 32 is placed on the charging pad, the receiver coil is inductively coupled to the magnetic flux generated by the coil in the charging pad which consequently induces a voltage in the receiver coil. The internal synchronous rectifier feeds this voltage to the RECT pin which has the filter capacitor C3.

The bq51003 identifies and authenticates itself to the primary using the COMM pins by switching on and off the COMM FETs and hence switching in and out C_COMM. If the authentication is successful, the transmitter will remain powered on. The bq51003 measures the voltage at the RECT pin, calculates the difference between the actual voltage and the desired voltage V_RECT-REG, (threshold 1 at no load) and sends back error packets to the primary. This process goes on until the input voltage settles at V_RECT-REG. During a load transient, the dynamic rectifier algorithm will set the targets specified by V_RECT-REG thresholds 1, 2, 3, and 4. This algorithm is termed Dynamic Rectifier Control and is used to enhance the transient response of the power supply.

During power up, the LDO is held off until the V_RECT-REG threshold 1 converges. The voltage control loop ensures that the output voltage is maintained at V_OUT-REG to power the system. The bq51003 meanwhile continues to monitor the input voltage, and maintains sending error packets to the primary every 250 ms. If a large overshoot occurs, the feedback to the primary speeds up to every 32 ms to converge on an operating point in less time.