User's Manual

UMXXX
whenever a new measurement is available. The inter-measurement period must be longer
than the selected timing budget plus 4ms.
The measurement timing budget can be set from 20 to 1000ms: increasing the timing
budget does increase the maximum distance and also reduce the repeatability error
(standard deviation of measurements), however power consumption increase accordingly:
• 20ms is the minimum timing budget, can be used only in short distance mode
• 33ms is the timing budget that can be used for all distance modes
• 140ms is the minimum timing budget which allows maximum distance of 4m in long
distance mode (dark ambient light and a 54% gray target).
The minimum ranging distance is 40mm; under this distance the sensor will detect a target
but the measurement will not be accurate. The maximum ranging distance depends on the
ambient light (the lower the better), on the reflectance of the target (the higher the better),
on the timing budget (the higher the better), on the selected ROI (the larger the better) and
on the selected ranging mode:
• short distance mode: ranging distance up to 1.3m, independent of ambient light and
target reflectance
• medium distance mode: ranging distance up to 2.9m in the dark, limited to 0.7m in
strong ambient light (200kcps/SPAD, direct illumination on the sensor in a sunny
day, infrared component removed by glass)
• long distance mode: ranging distance up to 1.7-3.6m in the dark for targets with 17-
88% reflectance, limited to ~0.7m in strong ambient light (specified as above);
longest ranging distance is 4m when timing budget is at least 140ms
The ranging error is typically between +/-20mm in the dark, and +/-25mm in strong ambient
light; the ranging error is the sum of the accuracy and the repeatability error:
• Accuracy is defined as the difference between the mean distance computed on 32
measurements and the actual distance; it can be affected by an offset error, a
temperature drift, and a voltage drift.
• The repeatability error is the standard deviation of the 32 measurements;
repeatability errors is reduced by increasing the timing budget; typical error is from
+/-1% down to +/-0.15%, depending on timing budget and ambient light.
The software driver provided by ST uses two parameters to qualify the ranging
measurement. The user application can disable the checks but ranging measurements may
be incorrect. The parameters are: