AutoResonant 5W wireless power transmitter features foreign object detection

A new wireless power transmitter, the LTC4125 has been introduced by Linear Technology. The simple high-performance monolithic full bridge resonant driver is capable of delivering up to 5W of power wirelessly to a companion receiver. It functions as the transmit circuit component in a complete wireless power transfer system comprised of transmit circuitry, transmit coil, receive coil and receive circuitry. The device improves upon a basic transmitter by providing three key features: an AutoResonant function that maximizes available receiver power, an Optimum Power Search algorithm that maximizes overall wireless power system efficiency, and foreign object detection (FOD) to ensure safe and reliable operation when working in the presence of conductive foreign objects. The LTC4125 automatically adjusts its drive frequency to match the LC network resonant frequency. This AutoResonant switching enables the device to deliver maximum power from a low voltage input supply (3V to 5.5V) to a tuned receiver such as Linear’s LTC4120 wireless receiver and battery charger via loosely coupled coils. Wireless power receivers can also be designed with the LTC4071 shunt battery charger or the LT3652HV multi-chemistry battery charger. To optimize system efficiency, the LTC4125 employs a periodic transmit power search and adjusts the transmission power based on the receiver load requirements. The device stops delivering power in a fault condition, or in the case of a detected foreign object.