P9027LP-R Datasheet

© 2016 Integrated Device Technology, Inc

13

April 28, 2016

Description of the Wireless Power System

Inductive wireless power transfer involves transmission of energy by changing the magnetic field from a power source to an electrical load,

without any connector, across an air gap. The DC power applied to the transmitter (Tx) creates an AC magnetic field in the transmitter coil.

Once the receiver (Rx) coil is placed near the magnetic field, the field will induce an AC current through the receiving coil where it is converted

into a DC current.

The communication between receiver and the transmitter is accomplished by modulating the load seen by the receiver's inductor. To the

transmitter, this appears as an impedance change, which results in measurable variations of the transmitter’s output waveform. Modulation is

accomplished with AC Modulation, using internal switches from LX1 and LX2 to ground.

The amount of power transferred is controlled by the receiver. The receiver sends communication packets to the transmitter to increase

power, decrease power, maintain the power level, or terminate the power transfer. The bit rate for Rx-to-Tx communication link is 2 Kbps. 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.

Theory of Operation

The P9027LP-R wireless power receiver works according to the magnetic induction (MI) principle. The Tx and Rx coils are coupled with a

coupling factor between 0.1 and 0.9, and power is transferred through an AC magnetic field.

The P9027LP-R is a highly-integrated wireless power receiver with a maximum output power of 3 Watts. It is designed to convert an AC

power signal from a resonant tank into a regulated output voltage. The device includes a high-efficiency synchronous full-bridge rectifier with

programmable w from 4.5 to 6.0 V. Programming is accomplished with a single external resistor on the VSET pin to ground.

The receiver utilizes IDT’s proprietary voltage clamping scheme which limits the maximum voltage at the rectifier pin to 9 V, reducing the

voltage rating on the output capacitors while eliminating the need for OVP and communication capacitors. As a result, it provides an

extremely small application area, making it an industry-leading wireless power receiver for high power density applications. Together with

P9235A-R transmitter, the P9027LP-R is a complete wireless power system solution.

The end of charge (EOC) pin is a logic input, which can be used with application processor or charger IC in battery management applications.

When asserted, it sends an end of charge packet to the transmitter, terminating the power transfer and shutting down the device. The

electrical on/off of the device is controlled through

EN

̅̅̅̅ pin. When connected to logic high, the device shuts down and consumes minimum

current.

Communication Between the P9027LP-R and P9235A-R

When the P9027LP-R is placed on P9235A-R Tx coil, it responds to the transmitter's "ping" signal by rectifying the AC power from the

supply VDD, and thus, power up the internal control circuitry and logic inside the receiver. To increase the reliability of communication, an

internal load of approximately 20 mA is connected to VRECT until the external load is large enough to support communication.

During power up, the P9027LP-R communicates Signal Strength, Identification and Configuration packets to the transmitter, respectively.

Once the handshake between Rx and Tx has been established, the wireless power system is in the Power Transfer phase. The control loop

of the P9027LP-R then adjusts the rectifier voltage (based on load condition) by sending Control Error Packets instruction to the transmitter.

During power delivery to the load, the P9027LP-R control circuit continues to send Control Error Packets to the transmitter to adjust the

operating frequency, and thus rectifier voltage, to the level required to maximize the efficiency of the linear regulator.

Over-Voltage Protection

One of the common issues with wireless power receivers is the potential that the transmitter (TX) will transmit more power than the receiver

needs or can handle. This can happen when the coupling between the Tx and Rx increases due to a sudden move of the receiver. Because

of the slow communication, it may take up to a few seconds before the Tx can adapt its transmitting power, and this may be long enough for

the voltage on the LX and RECT pins to increase above the maximum ratings and damage the receiver.

For this reason, the P9027LP-R has over-voltage protection. In most wireless receiver chips, this is implemented by external clamping

capacitors. However, the P9027LP-R has implemented this feature internally to save board space and reduce the BOM cost. Furthermore,

since the clamping is activated around 8.5 V, the bulk capacitors can have a low voltage rating.