P9235A-R Datasheet

© 2016 Integrated Device Technology, Inc

10

May 17, 2016

Theory of Operation

General System Architecture

A wireless power transfer system has two sub-systems: the wireless power transmitter (Tx) and the wireless power receiver (Rx). The

transmitter makes power available through a full bridge/half bridge driven LC resonant tank. It transmits power through the generation of an

AC magnetic field. Once the receiver 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.

High Level Control Scheme

Wireless power systems adopt a set of pre-defined in-band communication commands as the close loop control strategy. The amount of

power transferred is controlled by the receiver. The receiver sends out Control Error Packets (CEP) to the transmitter to increase power,

decrease power, or maintain the power level. The transmitter responds by adjusting the switching frequency and/or duty ratio. The receiver

requests more power by sending out a CEP, which includes a positive numerical value. The communication is digital. The communication 1’s

and 0’s ride on top of the power link that exists between the two coils.

Wireless Power Communication

When the transmitter is not transferring power to the receiver, it is in the low power Standby Mode. While in this mode, in order to detect a

receiver, the transmitter sends out periodic analog and digital pings.

Analog pings are very short AC detection pulses. These short pulses do not transmit enough energy to wake up the receiver, only to detect its

presence. Digital pings, on the other hand, do transmit enough power to enable the receiver to wake up and begin communication. The

transmitter uses digital pings to listen for a response from a receiver. After the transmitter detects a receiver, it may extend the digital ping.

This causes the system to proceed to the Identification and Configuration phase.

Once the receiver is detected and powered up, it will send out communications packets to handshake with the transmitter. The first

communication packet the receiver sends out is the Signal Strength packet, followed by Identification packets and Configuration packets.

Once the handshake process is done, the receiver will send out periodic Control Error packets and Received Power packets to adjust the

power.

If the receiver needs to stop the power transfer, it will send out an End of Power Transfer (EPT) communication packet. The transmitter stops

transmitting power immediately, and starts pre-defined routines according to the information decoded from the EPT packet.

System Fault Protection

The wireless power transfer system implements system level protection. These include over voltage, under voltage, over current, and over

temperature protection. On the transmitter side, whenever a fault condition is detected, it shuts down the whole system immediately and

protects itself. If the receiver detects a fault condition, it will send the End of Power Transfer packets to shut down the system. The transmitter

will continue to transmit power from the time of the receiver fault detection to the reception of the End of Power Transfer packet.

action.

Over temperature protection: If the TS pin (pin 18) voltage falls below 600 mV (typical) then the transmitter will shut down. It will restart once

the TS voltage rises above 800 mV (200 mV hysteresis).