BQ50002 Datasheet, PDF (13/35 Pages) Texas Instruments – Low-Cost 5-V Wireless Power Transmitter Analog Front

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bq50002
SLUSBW1A – OCTOBER 2015 – REVISED OCTOBER 2015
Device Functional Modes (continued)
7.4.2 Communication
Communication within the WPC v1.2 specification is from the receiver to the transmitter. For example, in order to
regulate the output of the transmitter, the receiver sends messages requesting the transmitter to increase or
decrease power. The receiver communicates by modulating the rectifier voltage and using amplitude modulation
(AM) sends packets of information to the transmitter. A packet is comprised of a preamble, a header, the actual
message, and a checksum, as defined by the WPC standard.
The receiver sends a packet by modulating an impedance network. This AM signal reflects back as a change in
the voltage amplitude on the transmitter coil. In the bq500511/bq50002 system, the bq50002 performs the
demodulation function and passes a digitized version of the message to the bq500511 where the message is
decoded and processed. For example in response to a Control Error Packet, the bq500511 calculates the
required change in output power and in turn controls the bq50002 through the CLK_OUT, UP_DOWN, and
MODE pins to adjust the operating point and thus its output power.
The modulation impedance network on the receiver can either be resistive or capacitive. Figure 4 shows the
resistive modulation approach, where a resistor is periodically added to the load, resulting in an amplitude
change in the transmitter voltage. Figure 5 shows the corresponding capacitive modulation approach.
Rectifier
Receiver Coil
Receiver
Capacitor
Modulation
Resitor
Amax
A(0)
Operating state at logic “0”
Comm
A(1)
Operating state at logic “1”
Fsw
F, kHz
a)
b)
Figure 4. Receiver Resistive Modulation Circuit
Rectifier
Receiver Coil
Receiver
Capacitor
Modulation
Capacitors
Amax
A(0)
Operating state at logic “ 0”
Comm
A(1)
Operating state at logic “ 1”
Fsw
Fo(1) < Fo(0)
F, kHz
a)
b)
Figure 5. Receiver Capacitive Modulation Circuit
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