LX1972
PRODUCTION SPECIFICATION
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
WWW.Microsemi .COM
Ambient Light Detector
Copyright © 2004
Rev. 1.1b, 2005-10-31
TM ®
DESCRIPTION
The LX1972 is a low cost silicon
light sensor with spectral response that
closely emulates the human eye.
Patented circuitry produces peak
spectral response at 520nm, with IR
response less than ±5%, of the peak
response, above 900nm.
The photo sensor is a PIN diode array
with a linear, accurate, and very
repeatable current transfer function.
High gain current mirrors on the chip
multiply the PIN diode photo-current
to a sensitivity level that can be
voltage scaled with a standard value
external resistor. Output current from
this simple to use two-pin device can
be used directly or converted to a
voltage by placing it in series with a
single resistor at either of its two pins.
Dynamic range is determined by the
resistors (typically in the range of 10K
to 100K) and power supply values.
Typically the LX1972 needs only 1.8V
of headroom to operate at 1000 Lux
illumination.
Internal temperature compensation
allows dark current to be kept below
200nA over the full specification
temperature range (-40 to +85°C),
providing high accuracy at low light
levels. Usable ambient light conditions
range is from 1 to more than 5000 Lux.
The LX1972 is optimized for
controlling back lighting systems in low
cost consumer products such as LCD
TV, portable computers, and digital
cameras.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
Protected By U.S.Patents: 6,787,757; Patents Pending
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
PRODUCT HIGHLIGHT
LX1972
VDD
VSS
1.2V Typical
@ 100 Lux
VDD
VSS
Ambient Light LX1972 Top View
PACKAGE ORDER INFO
BC Plastic 1206
2-Pin
TA (°C)
RoHS Compliant / Pb-free
-40 to 85 LX1972IBC
Note: Available in Tape & Reel. Append the letters “TR” to
the part number. (i.e. LX1972IBC-TR)
L
LX
X1
19
97
72
2
LX1972
PRODUCTION SPECIFICATION
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
WWW.Microsemi .COM
Ambient Light Detector
Copyright © 2004
Rev. 1.1b, 2005-10-31
TM ®
ABSOLUTE MAXIMUM RATINGS
Supply Input Voltage ...........................................................................-0.3V to 6V
Ground Current..........................................................................Internally Limited
Operating Temperature Range.........................................................-40°C to 85°C
Maximum Operating Junction Temperature ................................................ 150°C
Storage Temperature Range.........................................................-40°C to +100°C
RoHS / Pb-free Peak Package Solder Reflow Temperature
(40 second maximum exposure) ..................................................... 260°C (+0, -5)
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to
Ground. Currents are positive into, negative out of specified terminal.
THERMAL DATA
BC Plastic 1206 2-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 850°C/W
Junction Temperature Calculation: TJ = TA + (PD x θJA).
The θJA numbers are guidelines for the thermal performance of the device/pc-board system. All of the
above assume no ambient airflow.
PACKAGE PIN OUT
1
2
VSS
VDD
BC PACKAGE
(Top View)
RoHS / Pb-free Gold Lead Finish
FUNCTIONAL PIN DESCRIPTION
Name Description
VDD Positive Terminal
VSS Negative Terminal
P
PA
AC
CK
KA
AG
GE
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D
DA
AT
TA
A
LX1972
PRODUCTION SPECIFICATION
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
WWW.Microsemi .COM
Ambient Light Detector
Copyright © 2004
Rev. 1.1b, 2005-10-31
TM ®
CHARACTERISTIC CURVES
Chart 1 – Response vs. wa velenght
0.0
0.5
1.0
1.5
2.0
2.5
-40-20 0 20406080
Temper atu r e (°C )
Op er ati n g V ol tag e
10µA
100µA
200µA
Chart 2 – Typical Operating Voltage Vs VSS Current
0
50
100
150
200
250
300
-40-20020406080100
Temp er atu re (° C )
Dark C urrent (nA)
Chart 3 – Dark Leakages Vs. Temperature
C
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LX1972
PRODUCTION SPECIFICATION
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
WWW.Microsemi .COM
Ambient Light Detector
Copyright © 2004
Rev. 1.1b, 2005-10-31
TM ®
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following specifications apply over the operating ambient temperature -40°C≤ TA ≤ 85°C except where
otherwise noted and the following test conditions: See Note 1, VDD =5V, RSS = 10K
LX1972
Parameter Symbol Test Conditions Min Typ Max
Units
` RESPONSE
Peak Spectral Response λPR 520 nm
Infrared Response )(I
)(I
PRDD
DD
λ
λ EV(550nm) = 292μW/cm2, Current responsivity
change with additional direct light input of
292μW/cm2 at 910nm, Note 3
5 1 5 %
EV = 14.6μW/cm2, ISS = 10μA 1.2 1.4
EV = 146μW/cm2, ISS = 100μA 1.8 2.1
Minimum Operational Voltage VDD-VSS
EV = 292μW/cm2, ISS = 200μA 2.2 2.6
V
EV = 14.6μW/cm2, Note 2 7.5 10 12.5
EV = 146μW/cm2, Note 2 75 100 125
Light Current ISS
EV = 292μW/cm2, Note 2; 150 200 250
μA
Gain Linearity 14.6μW/cm2 ≤ EV ≤ 146μW/cm2 @ 25°C -15 15 %
EV = 0μW/cm2, TA = 25°C 0.010 50
Dark Current IDD(DARK) EV = 0μW/cm2 200
nA
Power Supply Rejection Ratio PSRR VRIPPLE = 10mVP-P, f = 10kHz -25 dB
Radiant Sensitive Area 0.04 mm2
Notes:
1. The input irradiance (EV) is supplied from a white light-emitting diode (LED) optical source adjusted to impose the specified EV at a
peak λ = 550nm.
2. See Figure 1.
3. See Figure 2.
TEST CIRCUITS
LX1972
VSS
VDD
White
LED
10kΩ
Figure 1 – Operational Voltage Measurement Circuit
LX1972
VSS
VDD
White
LED 910nm
10kΩ
Figure 2 – IR Sensitivity Measurement Circuit
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LX1972
PRODUCTION SPECIFICATION
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
WWW.Microsemi .COM
Ambient Light Detector
Copyright © 2004
Rev. 1.1b, 2005-10-31
TM ®
SIMPLIFIED BLOCK DIAGRAM
Current
Amp
VDD
VSS
Figure 3 – Simplified Block Diagram
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 LX1972 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 LX1972 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 a 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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LX1972
PRODUCTION SPECIFICATION
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
WWW.Microsemi .COM
Ambient Light Detector
Copyright © 2004
Rev. 1.1b, 2005-10-31
TM ®
APPLICATION EXAMPLES
The following examples present both fully automatic
(no user input) and semi-automatic to fully manual
override implementations. These general guidelines are
applicable to a wide variety of potential light control
applications. The LX1972 can be used to control the
brightness input of CCFL inverters (like Microsemi’s
PanelMatch™ inverter family, or line of controller IC’s).
Likewise, it can interface well with LED drivers like the
LX1990 and LX1991 sink LED drivers, or boost drivers
like the LX1992, LX1993, LX1994, and LX1995.
In each specific application, it is important to recognize
the need to correlate the output current of the LX1972 for
the target environment and its ambient light conditions.
The mechanical mounting of the sensor, light aperture
hole size, use of a light pipe or bezel are critical in
determining the response of the LX1972 for a given
exposure of light.
R1
R2 C1
10µF
3V
To inverter brightness
input or LED driver
controller.
3.3V or 5V
VSS
VDD
Figure 4
The example in figure 4 shows a fully automatic
dimming solution with no user interaction. Choose R1
and R2 values for any desired minimum brightness and
slope. Choose C1 to adjust response time to filter 50/60
Hz room lighting. As an example, let’s say you wish to
generate an output voltage from 0.25V to 1.25V to drive
the input of an LED driver controller. The 0.25V
represents the minimum LED brightness and 1.25V
represents the maximum. The first step would be to
determine the ratio of R1 and R2.
R2111
0.25V
3.0V
R2R1 ×=−= ⎥
⎦
⎤
⎢
⎣
⎡
Next the value of R2 can be calculated based on the
maximum output source current coming from the
LX1972 under the application’s maximum light exposure,
lets say this has been determined to be about 50µA .
Thus R2 can be calculated first order as follows:
275KΩR211R125KΩ
50µA
1.25V
R2 =×=∴== ⎥
⎦
⎤
⎢
⎣
⎡
The output node will actually reach 1.25V when the source
current from the LX1972 is only about 44µA since about
6µA of current will be contributed from R1. This assumes a
high impedance input to the LED driver. In Figure 5 user
adjustable bias control has been added to allow control over
the minimum and maximum output voltage. This allows the
user to adjust the output brightness to personal preference
over a limited range. In addition, an equivalent DC voltage
may replace the PWM input source.
R1
40K R2
25K
10µF
To inverter
brightness input or
LED driver
controller input.
3.3V or 5V
VSS
VDD
3.3V PWM
Figure 5
Figure 6 shows how a fully manual override can be quickly
added to the example in figure 5. In addition to the gate to
turn on and off the LX1972, a diode has been inserted to
isolate the sensor when it is disabled.
30K 30K
10µF
To inverter
brightness input or
LED driver
controller.
VSS
VDD
PWM
CMOS
Gate
60K
3.3V
Disable
control
Figure 6
The preceding examples represent just a few of the
potential sensor applications. Further details and additional
circuits can be found in the application note (AN-28) LX1970
Visible Light Sensor located in the application section of our
website www.microsemi.com. Although this application note
is written around our LX1970 visible light sensor the circuits
can be easily adapted for use with the LX1972.
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LX1972
PRODUCTION SPECIFICATION
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
WWW.Microsemi .COM
Ambient Light Detector
Copyright © 2004
Rev. 1.1b, 2005-10-31
TM ®
APPLICATION CIRCUITS
VSS VDD
LX1972
LX1995
IN
SHDN
GND
SW
FB
SHDN
C1
4.7µF
R1
100K
GND
VIN
L1 10µH D1
UPS5817
C2
1µF
R6
15
R5
5.76K
R4
10K
C3
10µF
C4
0.1µF
R10
49.9K
R8
60.4K
3.3V
R7
24.9K
BACKLIGHT
MMBT2907
Figure 7 – Typical Application with Microsemi’s LX1995 LED Driver IC
VIN
S/P
BRT
LS
GND
DRV
SRC
OVP
FB
CMP
22µH
FDN337
UPS5819
1M
41.2K
0.1µF
4.99K
1µF
15K
22µF
178K
100K
VDD VSS
3.3V
1µF
15
VIN = 2.0V to 5.5V
PWM Dimming Input
LX1972
LX1994
MMBT2907
Figure 8 – Typical Application with Microsemi’s LX1994 LED driver IC
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LX1972
PRODUCTION SPECIFICATION
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
WWW.Microsemi .COM
Ambient Light Detector
Copyright © 2004
Rev. 1.1b, 2005-10-31
TM ®
PACKAGE DIMENSIONS
BC 2-Pin 1206 Standard Carrier
D
P
H
E
Side
Top
Bottom
1
2
1
A
X
R
Pin 1 Indicator
2
M
B
CL
CL
0.03
0.19 - 0.25mm
Sensor Active
Area: 0.2 x 0.2mm
Sensor Active Area
MILLIMETERS INCHES
Dim MIN MAX MIN MAX
A 0.95 1.25 0.037 0.049
B 0.40 0.70 0.016 0.028
D 3.05 3.35 0.120 0.132
E 1.85 2.15 0.073 0.085
H 0.40 0.60 0.016 0.024
M 3° nom 3° nom
P 1.45 1.75 0.057 0.069
R 0.25 nom 0.010 nom
X 0.02 0.05
0.0008 0.002
Note:
Dimensions do not include protrusions; these shall not excee
0.155mm (.006”) on any side.
1.50mm
0.06in.
2.0mm
0.08in.
1.50mm
0.06in.
1.50mm
0.06in.
Super Imposed
1206 Package
Recommended Soldering Pattern for reflow soldering of the
BC (1206) package.
Basic specification is < 5 seconds @ 260°C when applying
solder.
8.00
5.25
1.75
4.00
2.00
4.00
Lead In: 10 min empty
Loaded: 3000 pcs
Lead Out: 40 min empty
1.30
0.20
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LX1972
PRODUCTION SPECIFICATION
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
WWW.Microsemi .COM
Ambient Light Detector
Copyright © 2004
Rev. 1.1b, 2005-10-31
TM ®
NOTES
PRODUCTION DATA – Information contained in this document is proprietary to
Microsemi and is current as of publication date. This document may not be modified in
any way without the express written consent of Microsemi. Product processing does not
necessarily include testing of all parameters. Microsemi reserves the right to change the
configuration and performance of the product and to discontinue product at any time.
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