TSL25721 datasheet(15/41 Pages) OSRAM

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TSL2572 − Principles O f Operation

Photodiodes

Conventional ALS detectors respond strongly to infrared light,

which the human eye does not see. This can lead to significant

error when the infrared content of the ambient light is high

(such as with incandescent lighting).

This problem is overcome through the use of two photodiodes.

The Channel 0 photodiode, referred to as the CH0 channel, is

sensitive to both visible and infrared light, while the Channel 1

photodiode, referred to as CH1, is sensitive primarily to infrared

light. Two integrating ADCs convert the photodiode currents to

digital outputs.The ADC digital outputs from the two channels

are used in a formula to obtain a value that approximates the

human eye response in units of lux.

ALS Operation

The ALS engine contains ALS gain control (AGAIN) and two

integrating analog-to-digital converters (ADC), one for the CH0

and one for the CH1 photodiodes. The ALS integration time

(ATIME) impacts both the resolution and the sensitivity of the

ALS reading. Integration of both channels occurs

simultaneously and upon completion of the conversion cycle,

the results are transferred to the data registers (C0DATA and

C1DATA). This data is also referred to as channel count. The

transfers are double-buffered to ensure data integrity.

Figure 17:

ALS Operation

CH1

ADC

ALS Control

CH1

Data

CH0

ALS

CH0

Data

AGAIN(r0x0F, b1:0)

y, 8y, 16y, 120y Gain

CH0

CH1

C0DATAH(r0x15), C0DATA(r0x14)

C1DATAH(r0x17), C1DATA(r0x16)

ATIME(r 1)

2.73 ms to 699 ms

AGL(r0x0D, b2)

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