designfeature
Sam DaviS, Editor-in-Chief, PET
Wireless Power Receiver IC
Complements Existing Transmitter
A wireless Power Receiver,
the bq51013, complements the bq500110 Power
Transmitter introduced about
six months ago. Both TI ICs
comply with Wireless Power
Consortium (WPC) Qi Standard
Version 1.0.2 (April 2011) for
wireless power transfer based
on near field magnetic induction between planar coils.
W
ireless power transfer employs a Power Transmitter with a
primary coil that creates a magnetic field on a charging pad.
When placed on the charging pad, a secondary coil that has
an associated wireless Power Receiver converts the induced
magnetic field into a dc output voltage. The bq51013 is a
wireless Power Receiver IC with full-bridge synchronous
rectification, voltage conditioning and wireless power control
(Fig. 1). The bq51013:
• Complies with the WPC Qi Standard, producing up to 5W (5V @1A)
• Enables powering or charging from TI’s bq500110 or any available Qi-compliant
transmitter.
• Has 93% peak rectification efficiency that reduces thermal rise inside the system
while allowing charge rates comparable to an AC adapter.
• Has built in protection against voltage, current and temperature fault conditions,
ensuring safe and reliable system operation.
• Integrates voltage conditioning and full wireless power control
• Is housed in a 1.9-mm x 3-mm WCSP package
The bq51013 allows designers to integrate wireless power technology into their
existing and new applications with minimal impact on solution size. It is intended
for portable consumer devices such as smart phones, gaming systems, digital cameras,
along with medical and industrial equipment.
The Power Receiver works with the Power Transmitter in a wireless power transfer system. The bq51013 Power Receiver controls the power transferred by sending
feedback (error signal) communication to the Power Transmitter’s primary coil (e.g.
to increase or decrease power). The Power Receiver communicates with the Power
Transmitter by changing the load seen by the
transmitter. This load variation results in a
Power
bq51013
change in the transmitter coil current, which
is measured and interpreted by the Power
Voltage
AC to DC
Drivers
Rectification Conditioning
Load
Transmitter’s processor. Communication
involves digital packets transferred from the
Communication
Power Receiver to the Power Transmitter.
Differential bi-phase encoding is used for the
V/I
Controller
Controller
packets. The bit rate is 2-kbps. The WPC
Sense
Standard defines various types of communibq500110
cation packets, including identification and
authentication packets, error packets, control
Transmitter
Receiver
packets, end power packets, and power usage
packets.
The Power Transmitter’s coil stays powered
Fig. 1. Wireless Power Consortium (WPC or Qi) inductive power system includes a
off most of the time. Occasionally, it wakes
Power Transmitter (bq50010) and a Power Receiver (bq51013).
up to see if a receiver is present by transmit-
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July 2011 | Power Electronics Technology
15
WIRELESSIC
ting a “ping” to the Power
Receiver. When a Receiver
authenticates itself to the
transmitter, the transmitter remains powered on.
The receiver maintains full
control over the power
transfer using communication packets.
System
Load
Q1
USB or
AC Adaptor
Input
Bq51013
AD-EN
AD
C5
OUT
COMM1
C1
BOOT1
AC1
WIRELESS APPLICATION
C4
D1
RECT
R4
VTSB
R2
C3
COIL
C2
Fig. 2 shows a system that
TS/CTRL
uses the bq51013 as a 5V
AC2
NTC R3
power supply while power
BOOT2
CBOOT2
HOST
multiplexing the wired
COMM2
CHG
CCOMM2
3-State
(adapter) port. When
Bi-State
CLAMP2
CCLAMP2
placed on the charging
Bi-State
CLAMP1
CCLAMP1
pad, the Power Receiver
PGND
ILIM
coil couples inductively to
R1
the magnetic flux generated by the coil in the
charging pad, inducing a
voltage in the receiver coil. Fig. 2. Either the bq51013 used as a wireless Power Receiver and power supply or the AC adapter can be used for charging a
An internal synchronous battery (the system load).
rectifier feeds this voltage
to the RECT pin which has filter capacitor C3.
process goes on until the input voltage settles at VIN-REG.
The bq51013 identifies and authenticates itself to the
During a load transient, the dynamic rectifier algorithm
Power Transmitter’s primary coil by switching COMM1 and
enhances the power supply’s transient response.
COMM2 in and out. If the authentication is successful, the
A voltage control loop maintains the output voltage at
Power Transmitter remains powered on. The bq51013 meaVOUT-REG (~5V for the bq51013) to power the system load
sures the voltage at the RECT pin, calculates the difference
(charge a battery). The bq51013 meanwhile continues to
between the actual voltage and the desired voltage, VRECTmonitor the input voltage, and maintains sending error packets to the primary every 250ms. If a large transient occurs,
,
(~7V
for
the
bq51013
at
no
load)
and
sends
back
error
REG
the feedback to the primary speeds up to every 32ms in
packets to the primary coil in the Power Transmitter. This
■ WPC WIRELESS POWER STANDARD
THE WIRELESS POWER CONSORTIUM (WPC)
refers to a Base Station as a provider of
wireless power and a Mobile Device as a
consumer of that wireless power. The Base
Station usually has a charging pad and
the Mobile Device is placed on the pad to
it can charge a battery. The Base Station
contains a Power Transmitter with a primary coil and the Mobile Device contains a
Power Receiver with a secondary coil. The
primary and secondary coils form the two
halves of a coreless resonant transformer
that transfers power from the Base Station
to the Mobile Device. The WPC Standard:
• Enables wireless transfer of about 5 W,
16
using an appropriate secondary coil with a
typical outer dimension of about 40 mm.
• This resonant power transfer system
operates between 110 and 205 kHz.
• There are two possible methods for placing the Mobile Device on the surface of the
Base Station:
• Guided Positioning helps a user properly
place the Mobile Device on the surface of
a Base Station that provides power through
a single or a few fixed locations of that
surface.
• Free Positioning enables arbitrary placement of the Mobile Device on the surface
of a Base Station that can provide power
Power Electronics Technology | July 2011
through any location on that surface.
• A simple communications protocol
enables the Power Receiver in the Mobile
Device to control the transfer of power.
• Exhibits very low standby power (implementation dependent).
Typically, power transfer from a Power
Transmitter to a Power Receiver consists
of four phases:
• In the selection phase, the Power
Transmitter monitors the interface surface
for the placement and removal of objects.
Initially, if it does not have sufficient
information for this, the Power Transmitter
repeatedly pings the Power Receiver. If
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order to converge on an operating point
BOOT2
in less time.
BOOT1
If the input voltage suddenly increases (e.g. a change in position of the
equipment on the charging pad), the
voltage-control loop inside the bq51013
becomes active, and prevents the outAC1
put from going beyond VOUT-REG. The
AC2
Sync
receiver then starts sending back error
Rectifier
Control
packets to the transmitter every 30ms
until the input voltage comes back to
the VRECT-REG target, and then maintains the error communication every
250ms.
Fig. 3. The bq51013 has an integrated, self-driven synchronous rectifier that enables high-efficiency AC to DC
If the input voltage increases beyond power conversion. Capacitors from BOOT1 to AC1 and BOOT2 to AC2 aid in driving the high-side power MOSFETs
VOVP (overvoltage protection setting), of the synchronous rectifier.
the IC tells the primary coil to bring the
of 7V to ensure the VGS of the external PMOSFET (Q1) is
voltage back to VRECT -REG. In addition, a proprietary voltage protection circuit is activated by means of CCLAMP1 and
protected.
The bq51013 includes a ratiometric external temperaCCLAMP2 that protect the IC from voltages beyond the ICís
ture sense function. The temperature sense function has two
maximum rating (e.g.20V).
ratiometric thresholds that represent a hot and cold condiFig. 2 is an example application that shows the bq51013
tion. An external temperature sensor is recommended to
used as a wireless power receiver that can multiplex between
provide safe operating conditions for the Power Receiver.
wired or wireless power for charging the selected battery. In
An integrated, self-driven synchronous rectifier in the
the default operating mode pins EN1 and EN2 are low,
bq51013 enables high-efficiency AC to DC power converwhich activates the adapter enable functionality. In this
sion. This rectifier consists of an all NMOS H-Bridge driver
mode, if an adapter is not present the AD pin will be low,
where the backgates of the diodes are configured to be the
and /AD-EN pin will be pulled to the higher of the OUT
rectifier when the synchronous rectifier is disabled (Fig. 3).
and AD pins so that the PMOSFET between OUT and AD
During the initial startup of the wireless system, the synwill be turned off. If an adapter is plugged in and the voltage
chronous rectifier is not enabled. At this operating point the
at the AD pin goes above 3.6V, wireless charging is disabled
DC rectifier voltage is provided by the diode rectifier. Once
and the /AD-EN pin goes to approximately 4 V below the
VRECT is greater than UVLO (undervoltage lockout), it
AD pin to connect AD to the secondary charger. The difference between AD and /AD-EN is regulated to a maximum
(continued on p 31)
the Power Transmitter does not select a
Power Receiver for power transfer and is
not actively providing power to a Power
Receiver for an extended amount of time,
the Power Transmitter goes to a standby
mode.
• In the ping phase, the Power Transmitter
executes a digital ping, and listens for a
response. If the Power Transmitter discovers a Power Receiver, the Power Transmitter
may extend the Digital Ping, i.e. maintain
the Power Signal at the level of the digital
ping. This causes the system to proceed to
the identification & configuration phase.
If the Power Transmitter does not extend
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the digital ping, the system reverts to the
selection phase.
• In the identification & configuration
phase, the Power Transmitter identifies
the selected Power Receiver, and obtains
configuration information such as the
maximum amount of power that the Power
Receiver intends to provide at its output.
The Power Transmitter uses this information to create a Power Transfer Contract
that contains limits for parameters that
characterize the power transfer. At any
time before proceeding to the power transfer phase, the Power Transmitter may
decide to terminate the extended digital
ping, which reverts the system to the selection phase.
• In the power transfer phase, the Power
Transmitter continues to provide power
to the Power Receiver, adjusting its primary coil current in response to control data that it receives from the Power
Receiver. Throughout this phase, the
Power Transmitter monitors the parameters that are contained in the Power
Transfer Contract. A violation of any of the
stated limits on any of those parameters
causes the Power Transmitter to abort the
power transfer - returning the system to the
selection phase.
July 2011| Power Electronics Technology
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