BQ500414Q Datasheet, PDF (23/34 Pages) Texas Instruments – Qi Compliant Wireless Power Transmitter Manager

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bq500414Q
SLUSBE4B – JANUARY 2014 – REVISED JUNE 2014
Typical Application (continued)
bq500414Q EVM is tested per CISPR25 EMI specification with and without the EMI shield. The measurement
results show > 24-dB improvement with the EMI shield at 5-W output power.
Peak Class 3 Limit
Peak Class 4 Limit
Peak Class 3 Limit
Peak Class 4 Limit
Figure 12. CISPR25 EMI Testing Result Without the EMI
Shield at 5-W Output Power
Figure 13. CISPR25 EMI Testing Result With the EMI
Shield at 5-W Output Power
10 Power Supply Recommendations
The device is designed to operate from an input voltage supply range between 3.0-V to 3.6-V, nominal 3.3-V.
The A6 Tx type requires 12-V system voltage. TPS40210 SEPIC converter is recommend to work with 6-V to 16-
V input.
11 Layout
11.1 Layout Guidelines
Careful PCB layout practice is critical to proper system operation. There are many references on proper PCB
layout techniques. A few good tips are as follows:
The Tx layout requires a 4-layer PCB layout for best ground plane technique. A 2-layer PCB layout can be
achieved though not as easily. Ideally, the 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 bq500414Q GND pins and the EPAD GND 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 bq500414Q. A good GND reference is necessary for proper bq500414Q
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.
The DC-DC buck regulator used from the 12-V input supplies the bq500414Q with 3.3-V. Typically a single-chip
controller solution with integrated power FET and synchronous rectifier or outboard diode is used. Pull in the
buck inductor and power loop as close as possible to create a tight loop. Likewise, the power-train, full-bridge
components should be pulled together as tight as possible. See the bq500414Q EVM for an example of a good
layout technique.
Copyright © 2014, Texas Instruments Incorporated
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