BQ50002 Datasheet, PDF (17/35 Pages) Texas Instruments – Low-Cost 5-V Wireless Power Transmitter Analog Front

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Typical Application (continued)
8.2.1 Design Requirements
bq50002
SLUSBW1A – OCTOBER 2015 – REVISED OCTOBER 2015
DESIGN PARAMETER
WPC coil type
8.2.2 Detailed Design Procedure
VALUE
A11
8.2.2.1 Capacitor Selection
Capacitor selection is critical to proper system operation. The total capacitance value of 4 nF × 100 nF is
required in the resonant tank. This is the WPC system compatibility requirement, not a guideline.
NOTE
A total capacitance value of 4 nF × 100 nF (C0G dielectric type, 50-V rating) is required in
the resonant tank to achieve the correct resonance frequency. The capacitors chosen
must be rated for at least 50 V and must be of a high-quality C0G dielectric (sometimes
also called NP0). These are typically available in a 5% tolerance, which is adequate. TI
does not recommend the use of X7R types or below if WPC compliance is required
because critical WPC Certification Testing, such as the minimum modulation or
guaranteed power test, might fail. The designer can combine capacitors to achieve the
desired capacitance value. Various combinations can work depending on market
availability. All capacitors must be of C0G types (not mixed with any other dielectric
types).
8.2.2.2 Current Monitoring Requirements
The bq50002 is WPC v1.2 ready. To enable the FOD feature, current monitoring is provided in the bq50002
Analog Front End. For proper scaling of the current monitor signal, the current sense resistor should be 20 mΩ.
For FOD accuracy, the current sense resistor must be a quality component with 0.5% tolerance, at least 1/4-W
rating, and a temperature stability of ±200 PPM.
8.2.2.3 Input Regulation
The bq500511 requires 3 VDC to operate. The regulator in the bq50002 provides this voltage rail eliminating the
need for any external regulation.
8.2.2.4 System Input Power Requirements
The design works with 5-V input voltage to the bq50002. The WPC defined A11 TX type requires 5-V system
voltage in order to deliver 5 W of output power from the receiver.
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