ST STEVAL-WBC2TX70 - Efficiency and Spatial Freedom in the Z-Axis; Figure 45. Y-Axis Offset Impact on Efficiency; Figure 46. Z-Axis Offset Impact on Efficiency

Figure 45. Y-axis offset impact on efficiency
6.6.5 Efficiency and spatial freedom in the Z-axis
Z-axis distance between the coils, also known as charging gap, is an additional parameter that significantly affects
charging performance. The STEVAL-WBC2TX70 was therefore also tested at various charging gap distances.
The same setup was used as for the previous test. Efficiency curves for various misalignments in the Z-axis are
shown in the figure below:
Figure 46. Z-axis offset impact on efficiency
Z-distance of 4 mm is a typical value for most applications.
Clearly, the transmitter can deliver sufficient power even with a 15 mm charging gap.
However, efficiency is decreasing rapidly with the increasing charging gap. Board temperature and ring node
voltage also usually increase with the charging distance. Therefore, minimizing Z-distance whenever possible is
recommended.
UM3286
STEVAL-WBC2TX70 description
UM3286 - Rev 1
page 62/84