Qi 5V wireless charger IC uses DSP control techniques

March 03, 2014 // By Graham Prophet
A single chip integrates all critical circuits in a tiny 5 x 5-mm package; NFC enables “smart” wireless charging, aimed initially at mobile phone applications

NXP has demonstrated what it says is a “revolutionary” Qi wireless charging transmitter device, which integrates all the circuits for a 5V mobile phone charger in an extremely small package measuring only 5-mm square. Using the NXP solution, fewer than 10 external components are needed to build a complete low-power 5V Qi A5/A11 wireless charging transmitter, alongside the Qi coil and resonant capacitors. The tiny footprint of the NXP NXQ1TXA5 system-on-chip means that the whole transmitter sits on a PCB of less than 1.5 cm 2 with components on a single side. This opens up possibilities for innovative wireless charging pad designs, including fitting the transmitter within the centre of the Qi coil. A video of NXP’s demonstration is here; http://youtu.be/ehGBI4blOtU

The NXQ1TXA5 system-on-chip integrates a power controller, digital signal processing (DSP), voltage regulation, Foreign Object Detection (FOD), a full-bridge power stage to drive the transmitter coil, and circuits for on-chip current and voltage measurement – leaving very few external components to complete the solution. Using the NXP CoolFlux DSP technology, the device is power efficient, achieving standby power of under 2 mW.

The reference design for the NXQ1TXA5 forms a complete wireless charger designed to meet low-power Qi A5/A11 specifications for 5V chargers and can be powered by standard USB wall chargers or PC USB ports. NXP’s high-efficiency GreenChip TEA1720 SMPS controller complements this low-power reference design to achieve overall low-power standby operation.

Two other reference designs in the NXP wireless charger transmitter devices family include the NXQ1TXA6, designed to meet the Qi A6 standard for 12V, as well as the NXQ1TXA1 which is designed to meet Qi A1/A10 standard for 19V charging transmitters. Both the NXQ1TXA1 and NXQ1TXA6 come in a small package of 7-mm square with only 32 pins spaced 0.5-mm apart for easy PCB design. NXP provides a complete low component count reference design based on NXQ1TXA1 and NXQ1TXA6, with other high-performing components of its portfolio