09/01/15

9

5W, QI WIRELESS POWER RECEIVER WITH INTEGRATED RECTIFIER AND LDO OUTPUT

P9025AC DATASHEET

Description of the Wireless Power Charging System

A wireless power charging system has a base station with one

or more transmitters that make power available via DC-to-AC

inverter(s) and transmit the power over a strongly-coupled

inductor pair to a receiver in a mobile device. The transmitter

may be a free-positioning or magnetically-guided type. A

free-positioning

type of transmitter has one coil or an array of

coils that offers limited spatial freedom to the end-user,

whereas a magnetically-guided type of transmitter helps the

end-user align the receiver to the transmitter with a magnetic

attraction.

The amount of power transferred to the mobile device is

controlled by the receiver. The receiver sends communication

packets to the transmitter to increase power, decrease power,

maintain the power level, or terminate power transfer. The bit

rate for Rx-to-Tx communication link is 2kbps. The

communication is digital and communication of 1's and 0's is

achieved by the Rx modulating the amount of load on the

receiver coil.

To conserve power, the transmitter places itself in a

very-low-power sleep mode unless it detects the presence of

a receiver. Once a receiver is detected, the transmitter exits

sleep mode and begins the power transfer per the WPC

specification.

Theory of Operation

The P9025AC is a highly-integrated WPC (Wireless Power

Consortium)-compliant wireless power receiver IC for mobile

devices. It can transfer 5W of power from a wireless

transmitter to a load (ex. a battery charger) in WPC "Qi" mode

using near-field magnetic induction. For complete details of

the WPC wireless power systems, refer to the WPC

specifications and other materials at

http://www.wirelesspowerconsortium.com.

Overview

The simplified internal block diagram of the P9025AC is

shown on page 8. An external inductor and capacitor transfers

energy from the transmitter's coil through the P9025AC's AC1

and AC2 pins to be full-wave-rectified and stored on a

capacitor exceeds the threshold of the VIN_UVLO block, the

rectification is performed by the body diodes of the

Synchronous Full Bridge Rectifier FETs. After the internal

biasing circuit is enabled, the Driver and Control block

operates the MOSFET switches in the rectifier synchronously

with the applied AC signal for increased efficiency. An internal

Using this information, the P9025AC sends instructions to the

wireless power transmitter to increase, maintain, or decrease

the amount of power transferred. The P9025AC may also

instruct the transmitter to terminate power transmission based

on various conditions and other inputs.

Power Control

sampled periodically and digitized by the ADC. The digital

equivalents of the voltage and current are supplied to the

internal control logic, which decides whether the loading

point is required. If the load is heavy enough to bring the

to move its frequency lower, closer to resonance. If the voltage

to increase its frequency. To maximize efficiency, the voltage

the LDO output voltage as the LDO's load current increases.

that the system can better handle a sudden load increase.

WPC Characteristics

Startup and Power Transfer

When a mobile device containing the P9025AC is placed on a

WPC "Qi" charging pad, it responds to the transmitter's "ping"

signal by rectifying the AC power from the transmitter and

internal linear voltage regulator provides the supply voltage for

the digital section to enable WPC communication. To increase

the reliability of the communication, an internal load of about

enough to support communication.

The P9025AC then communicates its Identification and

Configuration information to the transmitter. After this, the

system is in the Power Transfer state. The control loop of the

P9025AC then adjusts the rectifier voltage to 7V by sending

Control Error Packets instruction to the transmitter. The LDO

output is enabled and power is delivered to the load after

During power delivery to the load, the P9025AC control circuit

continues to send Control Error Packets to the transmitter to

adjust the rectifier voltage to the level required to maximize

the efficiency of the linear regulator.