bq51003
SLUSBC8 –DECEMBER 2013
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PRINCIPLE OF OPERATION
Power
bq51003
Voltage
Conditioning
AC to DC
Drivers
Rectification
Load
Communication
Controller
V/I
Sense
Controller
bq500210
Transmitter
Receiver
Figure 21. WPC Wireless Power System Indicating the Functional Integration of the bq51003
A Brief Description of the Wireless System:
A wireless system consists of a charging pad (transmitter or primary) and the secondary-side equipment
(receiver or secondary). There is a coil in the charging pad and in the secondary equipment which are
magnetically coupled to each other when the secondary is placed on the primary. Power is then transferred from
the transmitter to the receiver via coupled inductors (e.g. an air-core transformer). Controlling the amount of
power transferred is achieved by sending feedback (error signal) communication to the primary (that is, to
increase or decrease power).
The receiver communicates with the transmitter by changing the load seen by the transmitter. This load variation
results in a change in the transmitter coil current, which is measured and interpreted by a processor in the
charging pad. The communication is digital - packets are transferred from the receiver to the transmitter.
Differential Bi-phase encoding is used for the packets. The bit rate is 2-kbps.
Various types of communication packets have been defined. These include identification and authentication
packets, error packets, control packets, end power packets, and power usage packets.
The transmitter coil stays powered off most of the time. It occasionally wakes up to see if a receiver is present.
When a receiver authenticates itself to the transmitter, the transmiter will remain powered on. The receiver
maintains full control over the power transfer using communication packets.
Using the bq51003 as a Wireless Power Supply: (See Figure 2)
Figure 2 is the schematic of a system which uses the bq51003 as a power supply.
When the system shown in Figure 2 is placed on the charging pad, the receiver coil is inductively coupled to the
magnetic flux generated by the coil in the charging pad which consequently induces a voltage in the receiver coil.
The internal synchronous rectifier feeds this voltage to the RECT pin which has the filter capacitor C3.
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