Power Management
`
`Texas Instruments Incorporated
`
`An introduction to the Wireless Power
`Consortium standard and TI’s
`compliant solutions
`
`By Bill Johns
`Senior Applications Engineer
`Introduction
`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 con-
`figuration) 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 trans-
`mitter and requests more or less power. Commu ni ca tion is
`unidirectional from the power receiver to the power trans-
`mitter via backscatter modulation. In backscatter modula-
`tion, 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 communi-
`cations protocol between the two devices. These three
`areas are explored next.
`
`Figure 1. Typical wireless-power functional diagram
`
`Transmitter
`
`Power
`
`Receiver
`
`AC to DC
`
`Drivers
`
`Rectification
`
`Voltage
`Conditioning
`
`Load
`(Phone or
`Battery)
`
`Communication
`
`Controller
`
`V/I
`Sense
`
`Controller
`
`10
`
`High-Performance Analog Products
`
`www.ti.com/aaj
`
`1Q 2011
`
`Analog Applications Journal
`
`Apple v. GUI Global Products
`IPR2021-00471, 472, 473
`GUI Ex. 2032
`
`

`

`Texas Instruments Incorporated
`
`Power Management
`
`Power transmitter
`The direction of power transfer is always from the power
`transmitter to the power receiver. The key circuits of the
`power transmitter are the primary coil, used to transfer
`power to the power-receiver coil; the control unit for
`driving the primary coil; and the communications circuit
`for demodulating the voltage or current from the primary
`coil. Flexibility of the power-transmitter design is limited
`to provide consistent power and voltage levels to the
`power receiver.
`The power receiver identifies itself to the power trans-
`mitter as a compliant device and also provides configura-
`tion information. Once the transmitter initiates power
`transfer, the power receiver sends error packets to the
`power transmitter requesting more or less power. The
`power transmitter stops supplying power upon receiving
`an “End Power” message, or if no packets are received
`for more than 1.25 seconds. While no power is being
`transmitted, the power transmitter enters a low-power
`standby mode.
`The WPC specification allows for both fixed- and moving-
`coil configurations. A single fixed coil, referred to as type
`A1, is the solution that Texas Instruments (TI) supports.
`The power transmitter, typically a flat surface upon
`which the user places the power receiver, is connected to
`the power source. The coils of a WPC-compliant device
`operate as a resonant half bridge on a 50% duty cycle,
`with a 19-VDC input (±1 V). If more or less power is
`needed at the power receiver, the frequency in the coil
`changes but stays between 110 and 205 kHz, depending
`on power demands.
`Power receiver
`The power receiver is typically a portable device. The key
`circuits of the power receiver are the secondary coil, used
`to receive power from the power-transmitter coil; the rec-
`tification circuit, used to convert AC to DC; the power-
`conditioning circuit, which buffers the unregulated DC
`into regulated DC; and the communications circuit, which
`modulates the signal to the secondary coil. The power
`receiver is responsible for all communications of its
`authentication and power requirements, as the power
`transmitter is only a “listener.”
`While design of the power transmitter is restricted to
`keep it WPC-compliant, much more freedom is permitted
`for designing the power receiver. The coil dimension of the
`power receiver can be adjusted to meet the device’s form
`factor. The coil voltage at the power receiver is full-wave
`rectified, with a typical efficiency of 70% for a 5-V, 500-mA
`output. Because communication between the two devices
`is unidirectional, the WPC selected the power receiver to be
`the “talker.” Inductive power transfer works by coupling a
`magnetic field from primary to secondary coils. Uncoupled
`field lines rotate around the primary coil and do not repre-
`sent loss as long as the field lines don’t couple a parasitic
`load (for example, eddy-current loss in metal).
`
`Communications protocol
`The communications protocol includes analog and digital
`pinging; identification and configuration; and power trans-
`fer. A typical start-up sequence that occurs when a power
`receiver is placed on a power transmitter proceeds as
`follows:
`1. An analog ping from the power transmitter detects the
`presence of an object.
`2. A digital ping from the power transmitter is a longer
`version of the analog ping and gives the power receiver
`time to reply with a signal-strength packet. If the signal-
`strength packet is valid, the power transmitter keeps
`power on the coil and proceeds to the next phase.
`3. During the identification and configuration phase, the
`power receiver sends packets that identify it and that
`provide configuration and setup information to the
`power transmitter.
`4. In the power-transfer phase, the power receiver sends
`control error packets to the power transmitter to
`increase or decrease the power supply. These packets
`are sent approximately every 250 ms during normal
`operation or every 32 ms during large signal changes.
`Also during normal operation, the power transmitter
`sends power packets every 5 seconds.
`5. To end the power transfer, the power receiver sends an
`“End Power” message or sends no communications for
`1.25 seconds. Either of these events places the power
`transmitter in a low-power state.
`TI’s WPC-compliant solutions
`TI is a founding member of the WPC and has taken an
`active role in developing a robust wireless-power specifica-
`tion. TI has developed reliable solutions for both a power
`receiver and a power transmitter in the form of three newly
`developed ICs. The power receiver uses the MSP430bq1010
`and bq25046 devices. The power transmitter is based on
`the bq500110, which supports type A1 (single-coil) config-
`urations. Both receiver and transmitter ICs are designed
`to be interoperable with other WPC-compliant solutions.
`The MSP430bq1010 in the power receiver handles all
`of the logic functions and communications. The onboard
`analog-to-digital converters monitor the levels of voltage
`into and current out of the bq25046. The bq25046 provides
`load-current information to the MSP430bq1010, which then
`uses this information to control the power transmitter’s
`operating point. The bq25046 provides a low-current, 3.3-V
`low-dropout regulator (LDO) to power the MSP430bq1010
`and logic circuit, while a larger 5.0-V LDO is capable of
`providing up to 1 A of current to the main output.
`The power-transmitter solution is provided with the
`bq500110. This device demodulates and decodes serial
`data from the power receiver. The control circuits first
`
`Analog Applications Journal
`
`1Q 2011
`
`www.ti.com/aaj
`
`High-Performance Analog Products
`
`11
`
`Apple v. GUI Global Products
`IPR2021-00471, 472, 473
`GUI Ex. 2032
`
`

`

`Power Management
`
`Texas Instruments Incorporated
`
`TI Lit. #
`
`Document Title
`2. “Wireless Power Transmitter Manager,”
`bq500110 Data Sheet. . . . . . . . . . . . . . . . . . . . . . slusae0
`3. “1.1A, Single-Input 5-V Power Supply IC
`for Wireless Power Applications,” bq25046
`Data Sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . slusa83
`4. “Wireless Receiver-Side Communication and
`Power Monitoring IC for Wireless Power,”
`MSP430bq1010 Data Sheet. . . . . . . . . . . . . . . . . slas696
`5. “bq500110EVM-688 Evaluation Module,”
`User’s Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . slvu429a
`6. “bq25046EVM-687 Evaluation Module,”
`User’s Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . slvu420
`Related Web sites
`www.ti.com/wirelesspower
`www.ti.com/sc/device/partnumber
`Replace partnumber with bq25046, bq500110, or
`MSP430bq1010
`
`certify that the power receiver is indeed a WPC-compliant
`device, then configure the power transmitter accordingly.
`TI’s BQTESLA100LP EVM kit combines separate trans-
`mitter and receiver designs into a single kit that includes
`mechanical packaging. This kit can be used for evaluation
`of the ICs or as a design example. The WPC has certified
`that both the power-transmitter and the power-receiver
`solutions meet the Version 1.0 specification. No software
`is required to operate the EVM, which needs only a 19-V
`input. The EVM kit’s output will be 5 V at up to 1 A. The
`transmitter EVM includes multiple LED options for visual
`indication of power-transmission status. Also, two buzzer
`options provide audio indication of the start of power
`transfer.
`Conclusion
`The WPC standard is a set of guidelines that allows manu-
`facturers to develop solutions with the confidence that
`their components will mesh with a variety of other WPC-
`certified components designed for inductive power transfer.
`References
`For more information related to this article, you can down-
`load an Acrobat® Reader® file at www.ti.com/lit/litnumber
`and replace “litnumber” with the TI Lit. # for the
`materials listed below.
`
`Document Title
`1. Wireless Power Consortium. “System
`Description Wireless Power Transfer, Vol. 1,
`Part 1,” Version 1.0 [Online]. Available:
`http://www.wirelesspowerconsortium.com/
`downloads/wireless-power-specification-
`part-1.html
`
`TI Lit. #
`
`—
`
`12
`
`High-Performance Analog Products
`
`www.ti.com/aaj
`
`1Q 2011
`
`Analog Applications Journal
`
`Apple v. GUI Global Products
`IPR2021-00471, 472, 473
`GUI Ex. 2032
`
`

`

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