NXP finds a new use for near-field: wireless device charging

March 12, 2014

Bernard Cole-March 12, 2014

Before the end of this year, expect to see a variety of new mobile phones and other wirelessly connected consumer device incorporating NXP Semiconductor's new Qi wireless charging transmitter circuit building block.

The company expects to have reference designs by the beginning of summer and in mass production by fall with the Qi, which integrates all the circuits for a 5V mobile phone charger in an extremely small package measuring only 5-mm square.

Quite remarkable when compared with current approraches, in addition to a Qi coil and resonant capacitor, the circut requires fewer than 10 external components build a complete low-power 5V A5/A11 wireless charging transmitter..

According to Rick Dumont, marketing director, wireless charging solutions, the tiny footprint of NXP's NXQ1TXA5 system-on-chip means that the whole transmitter sits on a PCB of less than 1.5 cm-square with components on a single side. This opens up interesting possibilities for innovative wireless charging pad designs, including fitting the transmitter within the center of the Qi coil. (A video demonstration of the new chip is available on You Tube)

"By adding NFC, wireless chargers can offer a wide range of additional functionality," he said. "Consumers can configure wireless charging pad settings via any NFC-enabled phone or tablet, and NFC could be used to trigger “wake up” of the wireless charger, thus enabling zero standby current when not in use."

Other Qi smart features include automatic Bluetooth pairing, or launching applications and web sites when an NFC-enabled phone is put on the charging pad.

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. The device is extremely 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. An NXP TEA1720 SMPS controller complements this low-power reference design to achieve overall low-power standby operation.

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