8.1.1.1 Input Regulator

The bq500410A requires 3.3 V_DC to operate. A buck regulator or a linear regulator can be used to step down from the 12-V system input. Either choice is fully WPC compatible, the decision lies in the user's requirements with respect to cost or efficiency.

Figure 6 utilizes a low-cost buck regulator, TPS54231.

8.1.1.2 Power Trains

The bq500410A drives three independent half bridges. Each half bridge drives one coil from the coil set assembly. The TPS28225 is the recommended driver device for this application. It features high-side drive capability which enables the use of N-channel MOSFETs throughout. Gate-drive supply can be derived from a primitive active voltage divider. A highly regulated supply is not required to drive MOSFET gates.

8.1.1.3 Signal Processing Components

The COMM signal used to control power transfer is derived from the coil voltage. Each coil has its own signal processing chain. The coil voltage is AC coupled and divided down to a manageable level and biased to a 1-V offset. Series connected diodes are provided for protection from any possible transients. The three signal processing chains are then multiplexed together via analog switches. Thus, the correct signal processing chain and COMM signal used to control power transfer is from the coil being driven.

8.1.1.4 Low-Power Supervisor

Power reduction is achieved by periodically disabling the bq500410A while LED and housekeeping control functions are continued by U4, the low-cost, low quiescent current micro controller MSP430G2101. When U4 is present in the circuit (which is set by a pull-up resistor on bq500410A pin 25), the bq500410A at first power-up boots the MSP430G2101 with the necessary firmware and the two chips operate in tandem. During standby operation, the bq500410A periodically issues SLEEP command, Q1 pulls the supply to the bq500410A, therefore eliminating its power consumption. Meanwhile, the MSP430G2101 maintains the LED indication and stores previous charge state during this bq500410A reset period. This bq500410A off period is set by the MSP430G2101. WPC compliance mandates the power transmitter controller, bq500410A, awakes every 400 ms to produce an analog ping and check if a valid device is present. This time constant can not be altered to further reduce power.

8.1.1.5 Disabling Low-Power Supervisor Mode

For lowest cost or if the low-power supervisor is not needed, please refer to Figure 8 for an application schematic example.

8.1.1.6 Input Power Requirements

For full wireless power system capability and WPC compliance, the AC power adapter selected for the application should have a minimum rating of 12 V at 750 mA.