Wireless i c

7/31/2019 Wireless i c

1/3www.powerelectronics.com July 2011 | Power Electronics Technology 15

Sam DaviS, Editor-in-Chief, PET

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 synchronousrectification, 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 TIs 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 theirexisting 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 trans-

fer system. The bq51013 Power Receiver controls the power transferred by sending

feedback (error signal) communication to the Power Transmitters 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

change in the transmitter coil current, which

is measured and interpreted by the Power

Transmitters processor. Communication

involves digital packets transferred from the

Power Receiver to the Power Transmitter.

Differential bi-phase encoding is used for the

packets. The bit rate is 2-kbps. The WPC

Standard defines various types of communi-

cation packets, including identification and

authentication packets, error packets, control

packets, end power packets, and power usage

packets.

The Power Transmitters coil stays powered

off most of the time. Occasionally, it wakesup to see if a receiver is present by transmit-

A wireless Power Receiver,

the bq51013, comple-

ments 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 induc-

tion between planar coils.

Wireless Power Receiver ICComplements Existing Transmitter

designfeature

AC to DC Drivers

Power

Controller

bq500110

bq51013

Transmitter

V/I

Sense

LoadRectification

Communication

Controller

Receiver

VoltageConditioning

Fig. 1. Wireless Power Consortium (WPC or Qi) inductive power system includes a

Power Transmitter (bq50010) and a Power Receiver (bq51013).
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ting a ping to the Power

Receiver. When a Receiver

authenticates itself to the

transmitter, the transmit-

ter remains powered on.

The receiver maintains full

control over the power

transfer using communica-

tion packets.

WIRELESS APPLICATION

Fig. 2 shows a system that

uses the bq51013 as a 5V

power supply while power

multiplexing the wired

(adapter) port. When

placed on the chargingpad, the Power Receiver

coil couples inductively to

the magnetic flux gener-

ated by the coil in the

charging pad, inducing a

voltage in the receiver coil.

An internal synchronous

rectifier feeds this voltage

to the RECT pin which has filter capacitor C3.

The bq51013 identifies and authenticates itself to the

Power Transmitters primary coil by switching COMM1 and

COMM2 in and out. If the authentication is successful, thePower Transmitter remains powered on. The bq51013 mea-

sures the voltage at the RECT pin, calculates the differencebetween the actual voltage and the desired voltage, VRECT-

REG, (~7V for the bq51013 at no load) and sends back error

packets to the primary coil in the Power Transmitter. This

process goes on until the input voltage settles at VIN-REG.

During a load transient, the dynamic rectifier algorithm

enhances the power supplys transient response.

A voltage control loop maintains the output voltage atVOUT-REG (~5V for the bq51013) to power the system load

(charge a battery). The bq51013 meanwhile continues to

monitor the input voltage, and maintains sending error pack-

ets to the primary every 250ms. If a large transient occurs,

the feedback to the primary speeds up to every 32ms in

WIRELESSIC

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 pri-

mary 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,

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 plac-

ing 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 place-

ment of the Mobile Device on the surface

of a Base Station that can provide power

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 (imple-

mentation 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

USB orAC Adaptor

Input

Q1

Bq51013

AD-EN

AD

COMM1

BOOT1

AC1

AC2

BOOT2

COMM2

CLAMP2

CLAMP1

COIL

C1

R1

C2

CBOOT2

CCOMM2

CCLAMP2

CCLAMP1

ILIM PGND

OUT

RECT

VTSB

TS/CTRL

CHG

C4

D1

C3

SystemLoad

HOST

3-State

Bi-State

Bi-State

NTC R3

R2

R4

C5

Fig. 2. Either the bq51013 used as a wireless Power Receiver and power supply or the AC adapter can be used for charging a

battery (the system load).

WPC WIRELESS POWER STANDARD


3/3www.powerelectronics.com July 2011| Power Electronics Technology 17

order to converge on an operating point

in less time.

If the input voltage suddenly increas-

es (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 out-

put from going beyond VOUT-REG. The

receiver then starts sending back error

packets to the transmitter every 30ms

until the input voltage comes back to

the VRECT-REG target, and then main-

tains the error communication every

250ms.

If the input voltage increases beyond

VOVP (overvoltage protection setting),

the IC tells the primary coil to bring thevoltage back to VRECT -REG. In addition, a proprietary volt-

age protection circuit is activated by means of CCLAMP1 and

CCLAMP2 that protect the IC from voltages beyond the ICs

maximum rating (e.g.20V).

Fig. 2 is an example application that shows the bq51013used as a wireless power receiver that can multiplex between

wired or wireless power for charging the selected battery. In

the default operating mode pins EN1 and EN2 are low,

which activates the adapter enable functionality. In this

mode, if an adapter is not present the AD pin will be low,

and /AD-EN pin will be pulled to the higher of the OUT

and AD pins so that the PMOSFET between OUT and ADwill be turned off. If an adapter is plugged in and the voltage

at the AD pin goes above 3.6V, wireless charging is disabled

and the /AD-EN pin goes to approximately 4 V below the

AD pin to connect AD to the secondary charger. The differ-

ence between AD and /AD-EN is regulated to a maximum

of 7V to ensure the VGS of the external PMOSFET (Q1) is

protected.

The bq51013 includes a ratiometric external tempera-

ture sense function. The temperature sense function has two

ratiometric thresholds that represent a hot and cold condi-

tion. An external temperature sensor is recommended to

provide safe operating conditions for the Power Receiver.

An integrated, self-driven synchronous rectifier in the

bq51013 enables high-efficiency AC to DC power conver-

sion. This rectifier consists of an all NMOS H-Bridge driver

where the backgates of the diodes are configured to be the

rectifier when the synchronous rectifier is disabled (Fig. 3).During the initial startup of the wireless system, the syn-

chronous rectifier is not enabled. At this operating point the

DC rectifier voltage is provided by the diode rectifier. Once

VRECT is greater than UVLO (undervoltage lockout), it

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 discov-

ers 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

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 informa-

tion to create a Power Transfer Contract

that contains limits for parameters that

characterize the power transfer. At any

time before proceeding to the power trans-

fer phase, the Power Transmitter may

decide to terminate the extended digital

ping, which reverts the system to the selec-

tion phase.

In the power transfer phase, the Power

Transmitter continues to provide power

to the Power Receiver, adjusting its pri-

mary coil current in response to con-

trol data that it receives from the Power

Receiver. Throughout this phase, the

Power Transmitter monitors the param-

eters 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.

BOOT2

BOOT1

AC1

AC2 SyncRectifierControl

Fig. 3. The bq51013 has an integrated, self-driven synchronous rectifier that enables high-efficiency AC to DC

power conversion. Capacitors from BOOT1 to AC1 and BOOT2 to AC2 aid in driving the high-side power MOSFETs

of the synchronous rectifier.

(continued on p 31)

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