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AS7225

Optical Characteristics

Datasheet

• PUBLIC

DS000496

• v2-00 • 2019-Jun-28

│ 11

Optical Characteristics

The AS7225 contains an integrated tristimulus sensing element designed to meet the XYZ standard

observer response compliant with the CIE 1931 standard. The device contains a 16-bit integrating

analog-to-digital converter, which integrates current from the photodiodes. To ensure the integrity of

the data, upon completion of an integration cycle, results are transferred to double-buffered registers.

Standard observer tristimulus (XYZ) interference filters are applied to the Calibrated XYZ Chromatic

Smart Lighting Director optical channels as part of the CMOS process. This unique process enables

filter responses that mimic the human eye and is extremely stable over both operating temperature

and time. This in turn allows lifetime correlated color temperature (CCT) calibration to be performed as

part of the manufacturing process. Calibration is accomplished using standard white LEDs at a variety

of CCTs to deliver high accuracy and typically eliminate the need for light-by-light calibration in most

designs. Note, that any change of the pre-calibrated measurement conditions have an impact on the

accuracy of the measurement results. In such cases a design-level diffuser or color brightness

calibration is recommended to achieve highest accuracies. The AS7225 provides 2 calibration

matrices, a factory calibration and a second application specific matrix to optimize the measurement

performance. The additional calibration values will be set using the Smart Lighting Command Set

directives ATNORMGAIN and ATNORMINTT. These settings will be saved in the external flash and

reloaded automatically by the sensor firmware. See Section 12 for description of the complete Smart

Lighting Command Set.

The AS7225 LGA package contains an internal aperture that provides a package field of view (PFOV)

of ± 20.5°. External optics can be used as needed to expand or reduce this built in PFOV.

Sensor data readout to the maximum count value range is limited by the ADC. The maximum count

range value of 65535 is only reached with an integration time tINT of approximately 177.92ms. Below

that value, the FSR will be less than the maximum 16-bit /65536 count maximum as described in the

chart below.

Figure 7:

Overview Signal Resolution

Bit Resolution

tINT in ms

Maximum Counts

2.78

1024

5.56

2048

11.12

4096

22.24

8192

44.48

16384

88.96

32768

177.92

65536

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