An AutoResonant Wireless Power Transmitter Offers Foreign Object Detection

An AutoResonant Wireless Power TransmitterLinear Technology Corporation has introduced the LTC4125, a wireless power transmitter, developed for the wireless charging market. It is a simple, high performance monolithic full bridge resonant driver, capable of delivering up to 5W of power wirelessly to a companion receiver.

The LTC4125 wireless power transmitter 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 transmitter 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 multi­chemistry 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.

This transmitter simplifies wireless power systems with power optimization and foreign object detection. Applications include handheld instruments, industrial/military sensors and similar devices in harsh environments, portable medical devices, and electrically isolated devices. LTC4125­basedsystems 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) 20­pin 4mm x 5mm QFN package with backside metal pad for excellent thermal performance. The device is specified for operation from ­40°C to 125°C, in both E and I grades. Pricing for the transmitter starts at $4.00 in quantities of 1,000.