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MAX9635 Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX9635 Datasheet(HTML) 6 Page - Maxim Integrated Products |
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6 / 20 page  Industry’s Lowest-Power Ambient Light Sensor with ADC 6 Detailed Description The MAX9635 is an ambient light sensor with integrated photodiode and ADC with an I2C digital interface. To measure ambient light, the die is placed inside an optically transparent (OTDFN) package. A photodi- ode inside the IC converts the light to a current that is then processed by low-power circuitry into a digital bit stream. This is digitally processed and stored in an out- put register that is read by an I2C interface. An on-chip programmable interrupt function eliminates the need for continually polling the device for data and results in sig- nificant power saving. A package-level optical filter prevents ultraviolet and infrared from reaching the photodiode. Its opti- cal response is also designed to match the spectral response of the human eye. A second photodiode array, sensitive primarily to the infrared spectrum, is then used to match flourescent and incandescent light response from the part. Two key features of the IC analog design are its ultra-low current consumption (typically 0.65µA) and an extremely wide dynamic light range that extends from 0.045 lux to 188,000 lux—more than a 4,000,000 to 1 range. The on- chip autoranging scheme requires no user intervention for the gain-range setting. The IC can be customized to operate at enhanced sen- sitivity in applications where it needs to operate behind a dark glass. The default integration time of the ADC is 100ms, giving it inherent rejection of 50Hz and 60Hz ripple common in certain line-powered light sources. Human Eye CIE Curve and Different Light Sources The IC is designed to detect brightness in the same way as human eyes do. To achieve this, the sensor needs to have a spectral sensitivity that is similar to that of human eyes. Figure 1 shows the spectral sensitivity of the IC and the human eye (CIE curve). As can be seen, the human eye has its peak sensitivity at 555nm (green), while that of blue (~470nm) and red (~630nm) is much lower. The human eye also is blind to infrared (> 700nm) and ultraviolet (< 400nm) radiation. Light sources can have similar visible brightness (lux), but different IR radiation content (because the human eye is blind to it). The differences in the light spectra affect bright- ness measurement because some of this infrared radiation is picked up by silicon photodiodes. For example, light sources with high IR content, such as an incandescent bulb or sunlight, would suggest a much brighter environ- ment than our eyes would perceive them to be. Other light sources, such as fluorescent and LED-based systems, have very little infrared content. The IC exhibits good IR rejection and internal IR compensation scheme to minimize these effects and give an accurate lux response. Figure 1. Spectral Sensitivity of the MAX9635 and Human Eye WAVELENGTH (nm) CIE 900 800 700 600 500 400 20 40 60 80 100 120 0 300 1000 MAX9635 RESPONSE |
Similar Part No. - MAX9635_11 |
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Similar Description - MAX9635_11 |
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