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AS7225

Functional Description

Datasheet

• PUBLIC

DS000496

• v2-00 • 2019-Jun-28

│ 15

The AS7225 initial setup and ongoing parameter storage is automatically done by software within the

required external serial Flash memory, via SPI bus. Only ams-verified models of Flash devices can be

supported. A subset of supported devices is noted in the UART Command Interface section of this

document, which also provides a reference to the current list of supported Flash memory devices. For

the Flash memory, overview please refer to Figure 83. A SPI Flash device is a required operating

companion to the AS7225. Using other devices can cause communication issues and may not be

compatible. Flash timing is provided in Figure 81 and Figure 82.

A binary image software configuration tool is available from ams to allow the luminaire, lamp or driver

manufacturer to create their own “factory default” conditions that will be integrated with the ams–

supplied initial binary image to create a ready-to-program default Flash image. The configuration tool

is available from https://download.ams.com (see Smart Lighting Command Interface section).

XYZ white color point measurement is accomplished via nano-optic interference filters, which deliver a

CIE standard-observer type spectral response. As an extension of the CMOS processing of the

device, the filters are extremely stable over time and temperature. To minimize off-angle light

exposure and ensure accuracy, the AS7225 LGA package contains an internal aperture that limits the

sensor field of view (PFOV) of ± 20.5°, as shown in the Figure 1 above. External optics can be used

as needed to expand or reduce this built in PFOV.

For daylight operation, the AS7225 can be used two ways. As a standalone device pointing out of the

luminaire, or if pointing inward for white color, it can support daylighting operation by using an I²C

master connected (ams TSL25721 or TSL45315) for ambient light sensing. In either case, the AS7225

is the daylighting engine and directs the external MCU.

TSL25721 device combines a channel 0 (CH0) which is responsive to both visible and infrared light,

and channel 1 (CH1) which is responsive primarily to infrared light. Therefore, to get the LUX, a

calibration is necessary. In this calibration, both channels has to be considered. First counts per lux

(CPL) needs to be calculated in this calibration method.

Counts per LUX (CPL):

�� =

��0 − (1.87 ∗ ��1)

��

Calibration scalar:

�� = ��0 ∗ ��0 − ��1 ∗ ��1

Default setting K0 is 0.2178 (normal sunlight conditions in Europe in May, 1m distance to a window). If

K0=0, the result for K1 will be inverted to prevent negative LUX values. At different light conditions,

this value has to adjust.

Example:

Spectrometer value = 9764 Lux,

CH0 = 22870,

CH1 = 2734

→ CPL = 1.8186

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