TSL27711 datasheet(16/51 Pages) OSRAM

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TSL2771 − Principles Of Operation

Photodiodes

Conventional silicon 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) due to the

difference between the silicon detector response and the

brightness perceived by the human eye.

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) for the Channel

0 and Channel 1 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 18:

ALS Operation

CH1

ADC

ALS Control

CH1

Data

CH0

ALS

CH0

Data

AGAIN(r 0x0F, b1:0)

y, 8y, 16y, 120y Gain

CH0

CH1

C0DATAH(r 0x15), C0DATA(r 0x14)

C1DATAH(r 0x17), C1DATA(r 0x16)

ATIME(r 1)

2.72 ms to 696 ms

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