BQ500412 Datasheet, PDF (19/28 Pages) Texas Instruments – Low System Cost, Wireless Power Controller for WPC TX A6

bq500412
www.ti.com
SLUSBO2A – NOVEMBER 2013 – REVISED DECEMBER 2013
Input Regulator
The bq500412 requires 3.3 VDC to operate. A buck regulator or a linear regulator can be used to step down from
the 12-V system input. Either choice is fully WPC compatible, the decision lies in the user's requirements with
respect to cost versus efficiency. A buck regulator will offer higher efficiency and although slightly higher cost,it is
typically the better choice.
Power Train
The bq500412 drives three half bridges and only one of these bridges is activated at a time.
PCB Layout
A good PCB layout is critical to proper system operation and due care should be taken. There are many
references on proper PCB layout techniques.
Generally speaking, the system layout will require a 4-layer PCB layout, although a 2-layer PCB layout can be
achieved. A proven and recommended approach to the layer stack-up has been:
• Layer 1, component placement and as much ground plane as possible.
• Layer 2, clean ground.
• Layer 3, finish routing.
• Layer 4, clean ground.
Thus, the circuitry is virtually sandwiched between grounds. This minimizes EMI noise emissions and also
provides a noise free voltage reference plane for device operation.
Keep as much copper as possible. Make sure the bq500412 GND pins and the power pad have a continuous
flood connection to the ground plane. The power pad should also be stitched to the ground plane, which also
acts as a heat sink for the bq500412. A good GND reference is necessary for proper bq500412 operation, such
as analog-digital conversion, clock stability and best overall EMI performance.
Separate the analog ground plane from the power ground plane and use only one tie point to connect grounds.
Having several tie points defeats the purpose of separating the grounds.
The COMM return signal from the resonant tank should be routed as a differential pair. This is intended to reduce
stray noise induction. The frequencies of concern warrant low-noise analog signaling techniques, such as
differential routing and shielding, but the COMM signal lines do not need to be impedance matched.
Typically a single chip controller solution with integrated power FET and synchronous rectifier will be used. To
create a tight loop, pull in the buck inductor and power loop as close as possible. Likewise, the power-train, full-
bridge components should be pulled together as tight as possible. See the bq500412EVM-550, bqTESLA
Wireless Power TX EVM User's Guide (Texas Instruments Literature Number SLVU536) for layout examples.
References
1. Building a Wireless Power Transmitter, Application Report, (Texas Instruments Literature Number, SLUA635)
2. Technology, Wireless Power Consortium, www.wirelesspowerconsortium.com
3. An Introduction to the Wireless Power Consortium Standard and TI’s Compliant Solutions, (Johns Bill, Texas
Instruments)
4. Integrated Wireless Power Supply Receiver, Qi (Wireless Power Consortium), BQ51013 Datasheet, (Texas
Instruments Literature Number, SLUSAY6)
Copyright © 2013, Texas Instruments Incorporated
Product Folder Links: bq500412
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