P9221-R Datasheet

© 2017 Integrated Device Technology, Inc.

20

April 4, 2017

9. Communication Interface

9.1

Modulation/Communication

The wireless medium power charging system uses two-way communication: receiver-to-transmitter and transmitter-to receiver.

Receiver-to-transmitter communication is accomplished by modulating the load seen by the receiver's inductor; the communication is purely

digital and symbols 1’s and 0’s ride on top of the power signal that exists between the two coils. Modulation is done with amplitude-shift keying

(ASK) modulation using internal switches to connect external capacitors from AC1 and AC2 to ground (see Figure 17) with a bit rate of 2Kbps.

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

power transmitter detects this as a modulation of coil current/voltage to receive the packets.

Transmitter-to-receiver communication is accomplished by frequency-shift keying (FSK) modulation over the power signal frequency. The power

receiver P9221-R has the means to demodulate FSK data from the power signal frequency and use it in order to establish the handshaking

protocol with the power transmitter.

The P9221-R implements FSK communication when used in conjunction with WPC-compliant transmitters, such as the P9242-R. The FSK

communication protocol allows the transmitter to send data to the receiver using the power transfer link in the form of modulating the power

frequency. The P9221-R will only implement positive FSK polarity adjustments; in other words, the modulated frequency will always be higher

than the operating frequency during FSK communication.

Communication packets are transmitted from transmitter to receiver with less than 1% positive frequency deviation following any receiver-to-

transmitter communication packet. The frequency deviation is calculated using Equation 2.

60000

60000

− 3

[KHz]

Equation 2

is the internal oscillator responsible for counting the period of the power transfer signal.

The FSK byte-encoding scheme and packet structure comply with the WPC specification revision 1.2.2. The FSK communication uses a

Figure 18. Example of Differential Bi-phase Decoding for FSK

ONE

ZERO

ONE

ZERO

ONE

ONE

ZERO

ZERO

512 cycles

256 cycles

Each byte will comply with the start, data, parity, and stop asynchronous serial format structure shown in Figure 19:

Figure 19. Example of Asynchronous Serial Byte Format for FSK

Start

Stop

Parity

b

0

1

2

3

4

5

6

7

b

b

b

b

b

b

b