An introduction to the Wireless Power Consortium standard and TI’s solutions

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Wireless power is beginning to show great potential in the
consumer market. The ability to power an electronic
device without the use of wires provides a convenient
solution for the users of portable devices and also gives
designers the ability to develop more creative answers to
problems. This technology’s benefits can be seen in the
many portable devices, from cell phones to electric cars,
that normally operate on battery power.
Inductive coupling is the method by which efficient and
versatile wireless power can be achieved. For ease of use
and the benefit of both designers and consumers, the
Wireless Power Consortium (WPC) has developed a
standard (see Reference 1) that creates interoperability
between the device providing power (power transmitter,
charging station) and the device receiving power (power
receiver, portable device). Established in 2008, the WPC is
a group of Asian, European, and American companies in
diverse industries, including electronics manufacturers
and original equipment manufacturers (OEMs). The WPC
standard defines the type of inductive coupling (coil configuration)
and the communications protocol to be used
for low-power wireless devices. Any device operating
under this standard will be able to pair with any other
WPC-compliant device. One key benefit to this approach is
that it makes use of the coils for communications between
the power transmitter and the power receiver. See Figure 1
for a typical application diagram.
WPC standard for wireless power
Under the WPC standard, “low power” for wireless transfer
means a draw of 0 to 5 W. Systems that fall within the
scope of this standard are those that use inductive coupling
between two planar coils to transfer power from the power
transmitter to the power receiver. The distance between
the two coils is typically 5 mm. Regulation of the output
voltage is provided by a global digital control loop where
the power receiver communicates with the power transmitter
and requests more or less power. Communication
is
unidirectional from the power receiver to the power transmitter
via backscatter modulation. In backscatter modulation,
the power-receiver coil is loaded, changing the current
draw at the power transmitter. These current changes are
monitored and demodulated into the information required
for the two devices to work together.
The WPC standard defines the three key areas of the
system—the power transmitter that will supply power, the
power receiver that will use the power, and the communications
protocol between the two devices. These three
areas are explored next.
By Bill Johns
Senior Applications Engineer
Power Management
AC to DC Rectification
Load
(Phone or
Battery)
Drivers
Transmitter Receiver
Voltage
Conditioning
Controller Controller
Communication
Power
V/I