It’s convenient! No plugging in of tiny connectors, no mechanical wear, just place your device on the power transmitter and go!

Extra safety! Wireless power transfer allows fully enclosed devices with high isolation barrier. Great for devices that need to be waterproof or are used in wet environments.

Wireless charging of mobile phones is one of the most common applications nowadays, but there are many more situations where wireless power can be used, like power tools, shavers, toothbrushes and smart-watches.

Richtek now introduces RT1650, a robust and flexible wireless power receiver solution, fully compliant with WPC1.1 Qi standard and can be used for power transfer up to 7.5W.

The most common method of wireless electrical energy transfer is magnetic induction, which is the basic principle used by the Wireless Power Consortium (WPC) standard. The receiver inductor coil shares the transmitter inductor’s changing magnetic field and a voltage is induced in the receiver coil, which is then rectified and regulated. WPC Qi systems allow efficient power transfer over distances up to around 5mm between the two coils. A smart backscatter communication from receiver to transmitter keeps the system regulated and safe. Qi certified receivers are tested to work with Qi certified transmitters, providing good compatibility between many devices.

For more details of the Qi power transfer system and other wireless power standards:

• Highly integrated solution with on-board 32-bit ARM-Cortex-M0 MCU for all WPC communication, system monitoring and fault detections.
• Very flexible with a user configurable MTP memory. With default firmware, it is compliant with the WPC1.1 low power standard, providing output power up to 5W. With some firmware change it can meet WPC1.2.0 medium power standard for power up to 7.5W. RT1650 can also be configured to support the PMA standard.
• RT1650 includes a high efficiency fully synchronous rectifier stage, and a low drop 1.5A linear post regulator stage. A special headroom control system regulates the LDO headroom for optimal balance between transient response and system efficiency.
• Supports both adapter input and wireless power transfer input. Two MODE pins can be used to disable or enable specific inputs. Other features include NTC temperature sensing, programmable IC temperature control and operation mode signaling.

We took Nokia’s new generation wireless power transmitter at did a full application design and test with the RT1650 receiver. Here are some highlights:

• It is important to select the correct receiver coil and resonance capacitor values as they need to be tuned to the same 100kHz series resonance as Nokia DT601 transmitter according WPC1.1 standard. The resulting resonance curve of the transmitter – receiver coil combination is used to control the receiver output voltage by controlling the transmitter switching frequency between 110kHz and 205kHz range: As you can see from the graph, lowering transmitter frequency will result in higher receiver rectifier voltage.

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• The RT1650 application hardly requires any external components, and the configurable MTP memory makes it possible to fine-tune several parameters.
• The critical design components are the receiver coil and correct value of the resonance capacitors. For best efficiency, high quality receiver coil and resonance capacitors are recommended.
• If the receiver load exhibits load transients, it is important to examine the power stage aspects of the total system, and dynamic rectifier settings may need to be changed based on the open-loop transient behavior.
• Be sure to check the LDO power loss after changing rectifier voltage settings and IC layout should be optimized for IC cooling via PCB inner layers.
• The receiver application needs to be checked on the effects of metal shields and PCB ground planes nearby the receiver coil, and FOD settings may require some adjustment to compensate for the extra loss in PCB and shields.