Ambient light sensor produces digital output
Pacer
TSL2550
The first ambient light sensor that converts light intensity to a digital signal output capable of direct SMBus interface is now available from Pacer Components.
The first ambient light sensor that converts light intensity to adigital signal output capable of direct SMBus interface is nowavailable from Pacer Components.
The TSL2550, manufactured byTexas Advanced Optoelectronic Solutions (TAOS) is designed tohelp reduce overall system power by measuring the ambient oravailable light as a means of controlling display screenbacklighting in portable equipment such as laptop computers,mobile phones, PDAs, camcorders and GPS systems.
In addition toportable communications equipment the TSL2550 can also be used tomonitor lighting conditions for commercial and residentiallighting.
Display screen backlighting which can account for30-40% of total power can now be adjusted automatically with thehelp of this new single-chip light sensor.
This device will helpportable equipment users achieve significant power savings byadjusting display brightness to ambient conditions.
Research hasshown that portable equipment power consumption is directlyproportional to display luminance.
Dimming can reduce displaypower by as much as 70%.
The TSL2550 uses an all-silicontechnique that combines two photodetectors to measure ambientlight brightness as perceived by the human eye.
One of thephotodetectors is sensitive to both visible light and infra-redlight.
The second photodetector is sensitive to only infra-redlight.
The output of both detectors is converted to a digitalformat and stored in separate registers accessed through theSMBus.
The combined information compensates for the effect of theinfra-red content of ambient light, thereby approximating theresponse of the human eye.
This information can be used tocalculate light intensity in commonly used units of lux.
Thistechnique eliminates the need to use an expensive photopicfilter.
Additionally the ratio of infra-red light to visiblelight can be used to determine the type of ambient light source(incandescent, fluorescent or sunlight) thereby allowing moreintelligent control of display contrast and/or colour.
TheTSL2550 uses a companding analogue to digital convertor toprovide light measurements over an effective 12bit dynamic range.The integrating conversion technique used by the TSL2550effectively eliminates the effect of flicker from AC poweredlamps, thereby increasing the stability of the measurement.
Asingle supply operation (2.7 to 5.5V) makes this device wellsuited for use in 3V systems.
Moreover a power-down mode, whichshuts off the device on command when not in use, ensures that theTSL2550 consumes as little power as possible.
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