TSL2561 datasheet(24/37 Pages) OSRAM

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ams Datasheet

Page 23

[v1-01] 2018-Apr-23

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TSL2561 − Device Operation

prevent transient changes in light intensity from generating an

unwanted interrupt. With a value of 1, an interrupt occurs

immediately whenever either threshold is exceeded. With

values of N, where N can range from 2 to 15, N consecutive

conversions must result in values outside the interrupt window

for an interrupt to be generated. For example, if N is equal to

10 and the integration time is 402ms, then an interrupt will not

be generated unless the light level persists for more than 4

seconds outside the threshold.

An interrupt is cleared by setting the CLEAR bit (bit 6) in the

Command Register.

To configure the interrupt as an end-of-conversion signal, the

interrupt PERSIST field is set to 0. An interrupt will be generated

upon completion of each conversion. The interrupt threshold

registers are ignored.

In order to generate an interrupt on demand during system test

or debug, a test mode (INTR = 11) can be used.

Calculating Lux

The TSL2561 is intended for use in ambient light detection

applications such as display backlight control, where

adjustments are made to display brightness or contrast based

on the brightness of the ambient light, as perceived by the

human eye. 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 in the TSL2561 through the use of

two photodiodes. One of the photodiodes (channel 0) is

sensitive to both visible and infrared light, while the second

photodiode (channel 1) is sensitive primarily to infrared light.

An integrating ADC converts the photodiode currents to digital

outputs. Channel 1 digital output is used to compensate for the

effect of the infrared component of light on the channel 0

digital output. The ADC digital outputs from the two channels

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

human eye response in the commonly used Illuminance unit of

Lux:

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