MAX44007(2010) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX44007
(Rev.:2010)

Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity

Maxim Integrated 

Low-Power Digital Ambient Light Sensor

with Enhanced Sensitivity

Detailed Description

The MAX44007 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 opti-

cally transparent (UTDFN-Opto) 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 0.025 lux to

104,444 lux—more than a 4,000,000 to 1 range. The on-

chip autoranging scheme requires no user intervention

for the gain-range setting.

As darkened glass or translucent materials can be trans-

parent to IR wavelengths while attenuating visible light

by 20–50 times or more, the IC dual-photodiode archi-

tecture can be utilized to compensate for the increased

IR component of incoming light. By allowing the user to

adjust the internal gain settings to compensate for the

dark glass’ profile, the IC excels in challenging low-light

level applications. contact the factory for more details.

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.

120

100

MAX44007 RESPONSE

80

60

40

CIE

20

0

300 400 500 600 700 800 900 1000

WAVELENGTH (nm)

Figure 1. Spectral Sensitivity of the MAX44007 and Human Eye

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