The OPT4001-Q1 has an automatic full-scale-range setting mode that eliminates the need to predict and set the best range for the device. Set the RANGE register to 0xC to enter this mode. The device determines the appropriate full-scale range to take the measurement based on a combination of current lighting conditions and the previous measurement.

If a measurement is towards the low side of full-scale, then the full-scale range is decreased by one or two settings for the next measurement. If a measurement is towards the upper side of full-scale, the full-scale range is increased by one setting for the next measurement.

If the measurement exceeds the full-scale range, resulting from a fast increasing optical transient event, then the current measurement is terminated. This invalid measurement is not reported. If the scale is not at the maximum, then the device increases the scale by one step and a new measurement is retaken with that scale. Therefore, during a fast increasing optical transient in this mode, a measurement can possibly take longer to complete and report than indicated by the CONVERSION_TIME configuration register.

Using this feature is highly recommended by Texas Instruments because the device selects the best range setting based on lighting conditions. However, there is an option to manually set the range. Setting the range manually turns off the automatic full-scale selection logic and the device operates for a particular range setting. Table 6-3 lists the range selection settings.