P9412 Datasheet

R35DS0011EU0120 Rev.1.2

Jul.6.21

Page 18

AC1

AC2

CMA

COM2

LDO VOUT

CMA

CM2

VRECT

COM1

CM1

CMB

CMB

Figure 6. Rx Modulation Components

Receiver-to-transmitter communication is accomplished by modulating the load applied to 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 done with AC modulation, using internal switches to connect

external capacitors from AC1 and AC2 to ground.

The P9412 communicates with the base via communication packets or decodes messages sent by WPC Rx’s.

Each communication packet has the following structure.

Preamble

Header

Message

Checksum

Figure 7

. Communication Packet Structure

According to the WPC specification, the power receiver communicates with the power transmitter using

backscatter modulation. The load seen by the power transmitter’s inductor is modulated on the receiver side to

send packets. The power transmitter demodulates these signals as a modulation of coil current/voltage to

decode and receive packets.

3.13.6.

Bit Encoding Scheme

As required by the WPC, the P9412 uses a differential bi-phase encoding scheme to modulate data bits onto the

power signal. A clock frequency of 2kHz is used for this purpose. A logic ONE bit is encoded using two narrow

transitions, whereas a logic ZERO bit is encoded using two wider transitions as displayed below.

tCLK

ONE

ZERO

ONE

ZERO

ONE

ONE

ZERO

ZERO

Figure 8. Bit Encoding Scheme

Each byte in the communication packet comprises 11 bits in an asynchronous serial format, as displayed below.

Start

Stop

Parity

b0

1

2

3

4

5

6

7

b

b

b

b

b

b

b

Figure 9. Byte Encoding Scheme