5W AutoResonant wireless power transmitter with FOD

November 30, 2015 // By Graham Prophet
LTC4125 is a wireless power transmitter configured as a simple, high performance monolithic full bridge resonant driver, capable of delivering up to 5W of power wirelessly to a companion receiver.

The device 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 (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 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. It is housed in a low profile (0.75mm) 20-pin 4 x 5 mm QFN package with backside metal pad for thermal performance. The device is specified for operation from ˗40C to 125C, in both E and I grades. Pricing starts at $4.00 (1000) for the E grade.

Linear Technology; www.linear.com/product/LTC4125

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