ST VL53L4CX - Customer Factory Calibration Functions; Refspad Calibration; Refspad Calibration Function; Refspad Calibration Procedure

6 Customer factory calibration functions
In order to benefit of full performance of the device, VL53L4CX driver includes calibration functions to be run once
on the customer production line.
Calibration procedures have to be run to compensate part to part parameters that may affect the device
performances.
Calibration data stored in the host have to be loaded in VL53L4CX at each startup using a dedicated driver
function.
Three calibrations are needed: refSPAD, crosstalk and offset.
The calibration functions are called in the following order:
1. refSPAD
2. crosstalk
3. offset
The three calibration functions can be done consecutively or individually. When run individually, the previous
calibration function has to be loaded before running calibration.
6.1 RefSPAD calibration
The number of single photon avalanche diode (SPAD) is calibrated during final module test (FMT) at ST. This part
to part value is stored into the device's NVM and automatically loaded in the device during boot.
This calibration allows the number of SPADs used by the device to be optimized.
However, adding a cover glass on top of the module may affect this calibration. ST recommends that the
customer performs this calibration in the final product application.
The same algorithm running at FMT is applied when this function is called. The algorithm searches three
locations:
• 1 (1 x attenuated SPADs)
• 2 (5 x attenuated SPADs)
• 3 (10 x attenuated SPADs).
The number of SPADs choosen is done to avoid signal saturation.
6.1.1 RefSPAD calibration function
The following function is available for SPAD calibration: VL53LX_PerformRefSpadManagement(VL53LX_DEV
Dev)
Note: This function must be called first in the calibration procedure.
The function can output the following three warning messages :
• VL53LX_WARNING_REF_SPAD_CHAR_NOT_ENOUGH_SPADS
Fewer than five good SPADs available, output not valid
• VL53LX_WARNING_REF_SPAD_CHAR_RATE_TOO_HIGH
At end of search reference rate > 40.0 Mcps Offset stability may be degraded.
• VL53LX_WARNING_REF_SPAD_CHAR_RATE_TOO_LOW
At end of search reference rate < 10.0 Mcps. Offset stability may be degraded.
6.1.2 RefSPAD calibration procedure
No particular conditions have to be followed for this calibration, except that no target should be placed on top of
the device.
Time to perform this calibration is only few milliseconds.
This function has to be called after VL53LX_DataInit() function is called.
UM2923
Customer factory calibration functions
UM2923 - Rev 2
page 14/25