5W wireless power transmitter offers foreign object detection

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 LTC4125 wireless power transmitter improves upon a basic transmitter by providing three key features: an AutoResonant function that maximises available receiver power, an Optimum Power Search algorithm that maximises 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 (3 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 optimise 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.

Simplifying the wireless power system, these transmit power optimisation and foreign object detection features in the LTC4125 do not require any direct communication between the transmitter and receiver circuits. Without digital communication the LTC4125 can work over a wide range of transmit-to-receive coil coupling factors and avoid the need for complicated signal processing hardware and software to support a communication protocol.

The LTC4125 includes a programmable maximum current limit and an NTC input as additional means of foreign object and overload protection. Applications include handheld instruments, industrial/military sensors and similar devices in harsh environments, portable medical devices and electrically isolated devices. LTC4125-based systems offer robust, standalone solutions capable of large transmission distances up to 10mm and tolerance of poor coil coupling due to misalignment.

The LTC4125 is housed in a low profile (0.75mm) 20-pin 4mm x 5mm QFN package with backside metal pad for excellent thermal performance. The device is specified for operation from -40 to 125°C, in both E and I grades. 1,000-piece pricing starts at $4.00 each for the E grade.