BQ50002 Datasheet, PDF (12/35 Pages) Texas Instruments – Low-Cost 5-V Wireless Power Transmitter Analog Front

bq50002
SLUSBW1A – OCTOBER 2015 – REVISED OCTOBER 2015
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7.4 Device Functional Modes
7.4.1 Power Transfer
Power transfer efficiency and robustness depends on coil coupling. Coupling depends on the distance between
coils, alignment, coil dimensions, coil materials, number of turns, magnetic shielding, impedance matching,
frequency. Most importantly, the receiver and transmitter coils must be aligned for best coupling and efficient
power transfer. The smaller the space between the coils is, the better the coupling. Shielding is added as a
backing to both the transmitter and receiver coils to direct the magnetic field to the coupled zone. Magnetic fields
outside the coupled zone do not transfer power. Thus, shielding also serves to contain the fields to avoid
coupling to other adjacent system components.
Regulation can be achieved by controlling any one of the coil coupling parameters. However, for WPC
compatibility, the transmitter-side coils and capacitance are specified and the resonant frequency point is fixed.
In the bq500511/bq50002 system power transfer is regulated by changing the operating frequency between 110
kHz to 205 kHz. The higher the frequency, the further from resonance and the lower the power. Duty cycle
remains constant at 50% throughout the power band and is reduced only once 205 kHz is reached.
7.4.1.1 Dynamic Power Limiting™
Dynamic Power Limiting™ (DPL) allows operation from a 5-V supply with limited current capability (such as a
USB port). When the input voltage is observed drooping, the output power is dynamically limited to reduce the
load and provides margin relative to the supply’s capability.
Anytime the DPL control loop is regulating the operating point of the transmitter, the LED will indicate that DPL is
active. The LED color and flashing pattern are determined by the LED Table. If the receiver sends a Control
Error Packet (CEP) with a negative value, (for example, to reduce power to the load), the bq500511 in DPL
mode will return to normal operation and respond to this CEP via the standard WPC control loop behavior.
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