Feature Story
Introduction to RT1650, a Flexible
WPC Qi Compliant
7.5W Wireless Power Receiver Solution
Why wireless power transfer?
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.
How does wireless power transfer
work?
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:
Key features of wireless
power receiver RT1650
- 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.
A practical wireless power
transfer example – RT1650 receiver paired with Nokia DT601 transmitter
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.
Did you know … ?
- 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.
Read the full application
note on wireless power :
New Video:
Introduction to RT1650 video (Chinese spoken with English subtitles)
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