DocID026571 Rev 1 15/27
AN4545 Cover glass
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5 Cover glass
The VL6180X can be used with a cover glass. The cover glass can cause internal reflection
and this can be detected by VL6180X as unwanted signals. This is known as the cross talk.
The cross talk can affect the range output, hence we recommend the user perform the cross
talk calibration procedure when using the VL6180X with cover glass (see Section 5.1.1).
The range ignore function should also be enabled to remove false detections from the cover
glass, see Section 5.1.2.
5.1 Range output
Figure 8 shows the impact of the cover glass on the range output of VL6180X. The internal
reflection between the glass and the VL6180X causes the ranging output to decrease at
longer distances.
This error in range is a ratio of the target signal rate and magnitude of the cross talk, hence
the range output from a darker target are more susceptible to the effect of cross talk.
Figure 9 shows the range output from VL6180X with the cross talk calibration procedure
implemented. The range error caused by the cover glass is corrected.
Note: The offset might need to be re-calibrated when ranging though cover glass.
The cross talk rate depends on the glass type and its placement relative to VL6180X. If the
glass type or its position changes, then cross talk calibration might need to be re-done.
Figure 8. Graph of range output vs. target distance without cross talk calibration. The
test was performed in the dark and with cover glass
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