User's Manual

UMXXX
8. Time-of-Flight sensor features
The VL53L1X is a state-of-the-art laser-ranging sensor in a miniaturized package. It
integrates a 940nm Class 1 vertical-cavity surface-emitting laser (VCSEL), a receiving
16x16 array of single-photon-avalanche-detectors (SPAD), physical infrared filters and
optics to achieve the best ranging performance. Unlike conventional ranging sensor,
VL53L1X measures the time-of-flight of photons emitted by the laser and reflected back by
the target. This allows an absolute distance measurement, which is independent of target
color or reflectance.
The field-of-view (FoV) is programmable from 15 to 27 degrees. When the full array of
SPAD is used the FoV is 27 deg; the FoV is reduced by selecting a subset, known as region-
of-interest (ROI), in the SPAD array: 4x4 to 16x16 ROI size can be selected; the position of
the ROI in the array can also be set, in order to orient the FoV cone in a specific direction.
Reported values from the sensor are the ranging distance in mm, the return signal rate and
the ambient signal rate (kilo-count-per-second per SPAD, kcps), and the range status.
CALIBRATION FOR BEST PERFORMANCE
To get the best performance, it is advised to run calibration functions at least once after
assembly is completed. Calibration data must be stored in the host microcontroller and
loaded in VL53L1X at each startup.
• RefSPAD calibration (if used must be first called) should be used to optimize device
dynamic and accuracy: SPAD cells are classified as non-attenuated, attenuated by
5 or attenuated by 10; then SPAD are selected to avoid internal signal saturation.
This part-to-part value is computed during the final test at ST and stored in the non-
volatile memory (NVM), it is automatically loaded after boot. If a protective glass
cover is used on top of the device, it is recommended to perform this calibration.
• Offset calibration (call after RefSPAD and before Crosstalk) is to be performed
always after assembly is completed, to compensate for part-to-part variations,
reflow effects, and cover glass effects (if present).
• Crosstalk calibration (if used must be last called) is to be performed whenever there
is a protective cover glass on top of the device: crosstalk is the amount of light
reflected by the cover glass (not by the target); depending on glass quality the
crosstalk can be significant; when measured, the crosstalk can be compensated
internally by VL53L1X. Crosstalk compensation can be disabled.
RANGING MODE CONFIGURATION, DISTANCE AND ACCURACY
The sensor performs ranging continuously and autonomously with a programmable inter-
measurement period. If the interrupt pin is connected, the host will receive an interrupt