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PDF LX1972A Data sheet ( Hoja de datos )
| Número de pieza | LX1972A | |
| Descripción | Ambient Light Detector | |
| Fabricantes | Microsemi Corporation | |
| Logotipo |  |
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LX1972A
www.DataSheet4U.com
TM ® Ambient Light Detector
PRODUCTION DATA SHEET
DESCRIPTION
The LX1972A is a low cost silicon by placing it in series with a single
light sensor with a spectral response resistor at either of its two pins.
that closely emulates the human eye.
Dynamic range is determined by the
Patented circuitry produces peak resistors (typically in the range of 5K to
spectral response at 580nm, with an IR 100K) and the power supply values.
response less than ±5% of the peak Typically the LX1972A needs only
response, above 900nm.
2.7V of headroom to operate at 1000
The photo sensor is a PIN diode Lux illumination.
array with Microsemi’s Best Eye™ Internal temperature compensation
processing that provides a nearly allows dark current to be kept below
perfect photopic light wavelength 200nA over the full specification
response curve. LX1972A provides a temperature range (-40°C to +85°C),
linear, accurate, and very repeatable providing high accuracy at low light
current transfer function. High gain levels. Usable ambient light conditions
current mirrors on the chip multiply range is from 1 to more than 5000 Lux.
the PIN diode photo-current to a The LX1972A is optimized for
sensitivity level that can be voltage controlling back lighting systems in low
scaled with a standard value external cost consumer products such as LCD
resistor. Output current from this TV, portable computers, and digital
simple to use two-pin device can be cameras.
used directly or converted to a voltage
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
Protected By U.S. Patents: 6,787,757; Patents Pending
PRODUCT HIGHLIGHT
VDD
VDD
LX1972A
VSS
1.7V Typical
@ 100 Lux
VSS
KEY FEATURES
Near Human Eye Spectral
Response
Very Low IR Sensitivity
Highly Accurate & Repeatable
Output Current vs. Light
Scalable Output Voltage
Temperature Stable
Integrated High Gain Photo
Current Amplifiers
No Optical Filters Needed
APPLICATIONS
Portable Electronic Displays
LCD TV Backlight Systems
Digital Still Cameras (DSC)
Desk Top Monitors
Notebook Computers
Ambient Light
PACKAGE ORDER INFO
TA (°C)
Plastic 1206
BC 2-Pin
RoHS Compliant / Pb-free
-40 to 85
LX1972AIBC
Note: Available in Tape & Reel. Append the letters “TR” to
the part number. (i.e. LX1972AIBC-TR)
LX1972A
Copyright © 2005
Rev. 1.0, 2006-09-18
Microsemi
Integrated Products Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
1 page  
LX1972A
www.DataSheet4U.com
TM ® Ambient Light Detector
PRODUCTION DATA SHEET
SIMPLIFIED BLOCK DIAGRAM
LX1972A
VDD
Current
Amp
Figure 3 – Simplified Block Diagram
VSS
APPLICATION NOTE
LIGHT UNITS
In converting from µW/cm2 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 µW/cm2 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
µW/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/m2 = 100µW/cm2.
Therefore 14.6µW/cm2 = 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 LX1972A the peak photo response is at
580nm, 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 LX1972A the ATE
(Automatic Test Equipment) light source is configured with
white LEDs whose current is adjusted to output a calibrated
flux density. 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.
Copyright © 2005
Rev. 1.0, 2006-09-18
Microsemi
Integrated Products Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
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Hoja de datos destacado
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