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參數(shù)資料
| 型號(hào)： | LX1974IBC |
| 廠商： | MICROSEMI CORP-ANALOG MIXED SIGNAL GROUP |
| 元件分類： | 光電元器件 |
| 英文描述： | Ambient Light Detector |
| 中文描述： | LOGIC OUTPUT PHOTO DETECTOR |
| 封裝： | ROHS COMPLIANT, PLASTIC, 1206, 2 PIN |
| 文件頁(yè)數(shù)： | 5/9頁(yè) |
| 文件大?。?/td> | 352K |
| 代理商： | LX1974IBC |
LX1974
P
RODUCTION
D
ATA
S
HEET
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
W
M
.
C
Ambient Light Detector
Copyright
2005
Rev. 1.0, 2006-05-09
TM
S I M P L I F I E D B L O C K D I A G R A M
Current
Amp
VDD
VSS
Figure 3 –
Simplified Block Diagram
A P P L I C A T I O N N O T E
L
IGHT UNITS
In converting from
μ
W/cm
2
to lux it is necessary to
define the light source. Lux is a unit for the measurement
of illuminance, which is the photometric flux density or
visible light flux density. Whereas
μ
W/cm
2
is a
measurement of irradiance or the measurement of
electromagnetic radiation, flux both visible and invisible.
The first step in the conversion process is to convert
irradiance to illuminance, which essentially involves
running the irradiant flux through a photopic filter. In
normal ambient, a photopic curve is used and in dark
ambient, a scotopic curve (dark adapted eye) is used. If
the light is composed of only one wavelength, a
conversion chart will tell the conversion factor to convert
μ
W/m2 to lux (lumens/m2). If more than one wavelength
is used, the light spectrum of the irradiance must be
applied to the photopic filter to determine the resultant
illuminance. The most sensitive wavelength for the
normal light adapted human eye is 555nm, which
corresponds to yellowish-green light. At 555nm, the
conversion factor is 683 Lux = 1W/m
2
= 100
μ
W/cm
2
.
Therefore 14.6
μ
W/cm
2
= 100 lux at 555nm.
If the photo sensor had a truly photopic response, it would
produce the same output current for the same number of lux,
regardless of the color of the light. However, because the
match is not perfect, there is still wavelength dependency
particularly at the ends of the visible spectrum.
In the case of the LX1974 the peak photo response is at
520nm, however depending on the light source, what the
human eye perceives as ‘white’ light may actually be
composed of peak wavelengths of light other than 520nm.
For instance, a typical fluorescent lamp includes dominant
light not only near 550nm but also at 404 and 435nm.
Incandescent light sources such as standard tungsten lights
generate substantial IR radiation out beyond 2000nm.
For ease of automatic testing of the LX1974 the ATE
(automatic test equipment) light source is configured with
white LED’s whose current is adjusted to output a calibrated
flux density at 550nm. This allows consistent and repeatable
testing of the sensor but corresponds to a light source unlike
that typically found in an office, home or sunlit environment.
In practice, the user needs to place the sensor in the target
environment and calibrate the sensors output current range to
match the application objective. This is easily accomplished
by adjusting the output resistor, which sets the sensor’s gain.
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