BQ500110_11 Datasheet, PDF (8/25 Pages) Texas Instruments – Qi Compliant Wireless Power Transmitter Manager

bq500110
SLUSAE0A – NOVEMBER 2010 – REVISED APRIL 2011
FUNCTIONAL OVERVIEW
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The typical Wireless Power Transfer System consists of the primary and the secondary coils that are positioned
against each other in the way to maximize mutual coupling of their electromagnetic fields. Both coils have ferrite
shields as parts of their structure to even further maximize field coupling. The primary coil is exited with the
switching waveform of the transmitter power driver that gets its power from AC-DC wall adapter. The secondary
coil is connected to the rectifier that can either directly interface the battery or can have an electronic charger or
post-regulator connected to its output. The capacitors in series with the coils are tuned to create resonance in the
system. The system being in resonance facilitates better energy transfer compared to the inductive transfer.
Power transfer in the resonant system can also be easier controlled with the variable frequency control approach.
The rectifier output voltage is monitored by the secondary side microcontroller that generates signals to control
modulation circuit to pass coded information from the secondary side to the primary side. The coded information
is organized into information packets that have Preamble bytes, Header bytes, message bytes and the
Checksum bytes. Per WPC standard information packets can be related to Identification, Configuration, Control
Error, Rectified Power, Charge Status and End of Power Transfer. For detailed information on WPC standard
visit Wireless Power Consortium web site at http://www.wirelesspowerconsortium.com/.
There are two ways the coupled electromagnetic field can be manipulated to achieve information transfer from
the secondary side to the primary side. With resistive modulation approach shown in Figure 3, the
communication resistor periodically loads the rectifier output changing system Q factor and as a result value of
the voltage on the primary side coil. With capacitive modulation approach shown in Figure 4 a pair of
communication capacitors are periodically connected to the receiver coil network. These extra capacitance
application changes slightly the resonance frequency of the system and its response on the current operating
frequency, which in turn leads to coil voltage variation on the primary side.
With both modulation techniques primary side coil voltage variations are detected with demodulation circuit and
further interpreted in bq500110 to restore the content of the information packets and adjust controls to the
transmitter schematic.
Rectifier
Receiver Coil
Receiver
Capacitor
Modulation
Resitor
Modulation
a)
Figure 3. Resistive Modulation Circuit
Amax
A(0)
Operating state at logic “0”
A(1)
Operating state at logic “1”
Fsw
F, kHz
b)
8
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