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P9025AC Datasheet(PDF) 9 Page - Integrated Device Technology |
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P9025AC Datasheet(HTML) 9 Page - Integrated Device Technology |
9 / 20 page 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 connected to VRECT. Until the voltage across the 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 ADC monitors the voltage at VRECT and the load current. 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 The voltage at VRECT and the current through the rectifier are 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 conditions on VRECT indicate that a change in the operating point is required. If the load is heavy enough to bring the voltage at VRECT below its target, the transmitter is instructed to move its frequency lower, closer to resonance. If the voltage at VRECT is higher than its target, the transmitter is instructed to increase its frequency. To maximize efficiency, the voltage at VRECT is programmed to decrease and become closer to the LDO output voltage as the LDO's load current increases. When the load current is small, a higher VRECT is desirable so 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 storing it on a capacitor connected to VRECT. During the "ping" phase, the rectifier provides about 5V at the VRECT pin. An 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 15mA is connected to VRECT until the external load is large 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 VRECT initially reaches 7V. 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. |
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