MICROSEMI LX1971

LX1971
I N T E G R A T E D
Wide Range Visible Light Sensor
P R O D U C T S
P RODUCTION D ATA S HEET
KEY FEATURES
DESCRIPTION
Photo current is first multiplied by an
integrated high gain amplifier then the
square root is taken of the product of the
amplifier and an internal reference current.
Finally this is further multiplied converted
to current and made available at two
output pins; one a current source and the
other a current sink.
These currents can easily be converted
to voltage by adding a single resistor at
either or both outputs. Voltage gain is
determined by the resistor value typically
in the 5KΩ to 50KΩ range.
With accurate internal gain amplifiers
and square root transfer function, design
complexity and cost are greatly reduced.
The LX1971 is available in the Clear 8pin MSOP package.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
ƒ Approximate Human Eye
Spectral Response
ƒ Low IR Sensitivity
ƒ Highly Accurate &
Repeatable Output Current
vs. Light
ƒ Square root transfer function
ƒ Temperature Stable
ƒ Integrated High Gain Photo
Current Amplifiers
ƒ Complementary Current
Outputs
ƒ No Optical Filters Needed
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The LX1971 is a new technology light
sensor with spectral response that
emulates the human eye; it is pin to pin
compatible to Microsemi’s LX1970
visible light sensor however with a wider
dynamic range.
This device is ideal for monitoring
ambient light for the control of artificial
lighting, operation of shades, LED
signage and display, street lighting,
automotive light sensors and control of
backlight dimming. It has a unique photo
diode arrangement (patents pending) with
a peak response at 520nm while sharply
attenuating both ultra violet and infrared
wavelengths.
The photo sensor is a PIN diode array
with an accurate and very repeatable
current output.
BENIFITS
• Requires no wavelength
filters
• Insensitive to UV and IR
• More than 4 decades usable
light range
• Enables accurate lighting
control systems
PRODUCT HIGHLIGHT
VDD
4.7uF
VDD
25K
SNK
SNK
LX1971
0.60V Typ
VOUT
SRC
4.7uF
25K
0.45V Typ
SRC
GND
Ambient
Light
LX1971
PACKAGE ORDER INFO
Plastic MSOP
TA (°C)
DU 8-Pin
-40 to 85
LX1971IDU
Note: Available in Tape & Reel.
Append the letter “T” to the part number. (i.e. LX1971IDUT)
Copyright  2003
Rev. 1.0,2003-11-25
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1971
I N T E G R A T E D
Wide Range Visible Light Sensor
P R O D U C T S
P RODUCTION D ATA S HEET
PACKAGE PIN OUT
VDD ................................................................................................................. -0.3 to 6 VDC
SNK/SRC (Output Compliance Voltage)........................................... -0.3 to VDD + 0.3VDC
SNK/SRC (Maximum Output Current)................................................... Internally Limited
Operating Temperature Range ........................................................................ -40 to +85°C
Storage Temperature Range.............................................................................-55 to 125°C
Solder Reflow Peak Temperature (Soldering 10 seconds) ......................................... 240°C
VDD
1
8
VSS
NC
2
7
NC
NC
3
6
NC
SRC
4
5
SNK
Notes: 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.
active area
DU PACKAGE
(Top View)
Solder reflow to follow: IPC/JEDEC J-STD-020B 7/02 Pb-SN Small Body Profile
1
8
DU
6
1971
THERMAL DATA
xxxx
7
5
Plastic MSOP 8-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
206°C/W
39°C/W
THERMAL RESISTANCE-JUNCTION TO CASE, θJC
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ABSOLUTE MAXIMUM RATINGS
2
3
4
DU PACKAGE
(Bottom View)
xxxx = Denotes Date Code / Lot Information
FUNCTIONAL PIN DESCRIPTION
NAME
DESCRIPTION
VDD
Input Supply Voltage
VSS
Ground Reference for Power and Signal Output
SNK
Output Current Sink
SRC
Output Current Source
SIMPLIFIED BLOCK DIAGRAM
PACKAGE PHOTO
V DD
PACKAGE DATA
SNK
SRC
V SS
Copyright  2003
Rev. 1.0,2003-11-25
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX1971
I N T E G R A T E D
Wide Range Visible Light Sensor
P R O D U C T S
P RODUCTION D ATA S HEET
Parameter
LX1971
Typ
Min
Supply Voltage (VDD )
Max
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RECOMMENDED OPERATING CONDITIONS
Units
3¹
5.5
V
SNK Compliance Voltage Range
VSS +0.6
VDD
V
SRC Compliance Voltage Range
VSS
VDD - 0.75
V
SNK/SRC Output Resistor Range
5
100
KΩ
¹Outputs are functional down to VDD=2.7V
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following specifications apply over the operating ambient temperature -40°C ≤ TA ≤ 85°C, VDD = 3V to
5.5V, RLOAD= 25Kohms, Direct Light Input² of 584µW/cm2 except where otherwise noted. Performance between -40°C and 0°C and
between 70°C and 85°C are assured by design and characterization.
Parameter
Symbol
Supply Voltage Range
VDD
Input Supply Current
IDD
ISRC
ISRC
Output Current
ISNK
ISRC
ISRC
Output SNK/SRC Current Matching
IMATCH
Test Conditions
Min
LX1971
Typ
3
VDD = 3.0V, ISRC = 62µA, ISNK = open
VDD = 3.0V, Direct Light Input of
2
584µW/cm @ 25°C
VDD = 3.0V, Direct Light Input of
2
584µW/cm
VDD = 3.0V, Direct Light Input of
2
584µW/cm
VDD = 3.0V, Direct Light Input of
2
292µW/cm
VDD = 3.0V, Direct Light Input of
2
9.34µW/cm
Max
Units
5.5
VDC
350
590
750
µA
55
61
67
µA
52
61
70
-70
-61
-52
µA
34
41
48
µA
5.5
7
8.5
µA
2
6
%
VSS +0.45
VSS +0.6
V
VDD – 0.6
VDD – 0.7
V
VDD = 3.0V
VDD = 3.0V, @ 95% of nominal output
current
VDD = 3.0V, @ 95% of nominal output
current
SNKVMIN
SRC Maximum Compliance Voltage
SRCVMAX
SNK/SRC Output Dark Current
IDARK3.0V
VDD = 3V, No Light, 25°C
150
400
nA
SNK/SRC Output Dark Current
IDARK3.0V
VDD = 3V, No Light, -40°C to 70°C
450
1000
nA
SNK/SRC Output Dark Current
IDARK3.0V
VDD = 3V, No Light, 85°C
550
1150
nA
SNK/SRC Output Dark Current
IDARK5.5V
VDD = 5.5V, No Light, 25°C
320
nA
Wavelength of Peak Sensitivity
λPS
520
nm
Half Reception Angle
θ½
±60
deg
Supply Voltage Coefficient of Output
Current
Resolution Limit Due To Random Noise
Sensitivity Change @ 910nm
Radiant Sensitive Area
PSRR
IMIN
ISRC∆ IR
A
VDD = 3V to 5.5V
2.9
Minimum usable resolution
146
Current responsivity change with
2
additional direct light input of 584µW/cm
at 910nm, TA = 25°C, VDD = 3V
Photodiode Area
-10
0
.369
3.5
%/V
nW/cm
10
2
% of peak
mm
2
2
²The input irradiance is supplied from a white light-emitting diode (LED) optical source adjusted to impose 584µW/cm at 555nm on the sensor’s surface.
Copyright  2003
Rev. 1.0,2003-11-25
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
ELECTRICALS
SNK Minimum Compliance Voltage
LX1971
I N T E G R A T E D
Wide Range Visible Light Sensor
P R O D U C T S
P RODUCTION D ATA S HEET
Whereas the LX1970 has a responsiveness that is
directly proportional to the intensity of light falling on the
photo receptors. There are two different response equations
for the LX1971 depending on the operating range (intensity
of the light). Below 2500 lux, the response resembles a
square root function. Above 2500 lux, the response fits a
straight line curve.
I OUT =
(
LX1971 Calculated SRC Full Range Response
250
SRC Current (µA)
The LX1971 is a light sensor with a spectral response
that resembles the human visual system. It is packaged in
clear MSOP package with the same pin out and same
supply voltage range as Microsemi’s LX1970 light sensor.
The LX1971 responsiveness however differs from that of
the LX1970. In general the LX1971 has lower sensitivity
and a wider dynamic range.
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APPLICATION INFORMATION
200
150
100
50
0
0
)
5000
10000
15000
20000
25000
Incandescent Light (lux)
L × .808 + 1.1µA for L < 2500 lux
<2500 Lux Formula
I OUT = (L × .0083µA) + 23µA for 2500 lux < L <
>2500 Lux Formula
LX1971 Calculated SRC Low Level Response
20000 lux
The following curves show the calculated responsiveness of
the LX1971 without load resistors based on the formulas
above. They can be used as baseline guidelines to calculate
gain setting resistors. The compliance of the current source
output may result in premature saturation of the output when
load resistors are added. The SRC compliance voltage is
specified typically at VDD-600mV @ about 4000 lux.
SRC Current (µA)
40
30
20
10
0
0
500
1000
1500
2000
2500
Incandescent Light (lux)
<2500 Lux Formula
LX1971 Calculated SRC High Level Response
250
APPLICATIONS
The LX1971 is best suited for applications where the
system must respond to external events that affect the
user’s ability to see clearly. For example, a sensor to turn
on headlights or a sensor to adjust the reflectivity of a rear
view mirrors. These systems require the sensor to have
dynamic range similar to sight. Like the human eye, the
square root function of the LX1971 makes it extra sensitive
to small changes at lower light levels. The wide dynamic
range allows the LX1971 to sense the difference between
twilight and daylight or sunshine and heavy cloud cover.
50
SRC Current (µA)
The LX1970 is best suited for applications where the
light sensor is an integral part of a continuous lighting
control system. For example, in an LCD backlighting
application, the level of brightness of the backlight should
be adjusted in proportion to the level of ambient lighting;
the LX1970 can provide closed loop brightness control for
this type of system. For most indoor applications, the 2500
lux saturation point of the LX1970 is usually not a limiting
affect.
200
150
100
50
0
0
5000
10000
15000
20000
25000
Incandescent Light (lux)
>2500 Lux Formula
Copyright  2003
Rev. 1.0,2003-11-25
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1971
I N T E G R A T E D
Wide Range Visible Light Sensor
P R O D U C T S
P RODUCTION D ATA S HEET
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 LX1971 can be used for the control of artificial
lighting, operation of shades, LED signage and display,
street lighting, automotive light sensors and control of
backlight dimming.
In each specific application it is important to recognize
the need to correlate the sink and source current of the
LX1971 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 LX1971 for a given
exposure of light.
We are assuming a high impedance input to the LED driver.
In Figure 2 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. The PWM input source could
of course be replaced with an equivalent DC voltage.
3.3V or 5V
VDD
N/C
SNK
VSS
SRC
LED driver
controller or
dimming controller
input
10µF
3.3V PWM
R1
40K
3.3V or 5V
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APPLICATION EXAMPLES
R2
25K
VDD
VSS
SNK
N/C
Figure 2
SRC
3V
R1
R2
C1
10µF
Figure 3 shows how a fully manual override can be quickly
added to the example in figure 2. In addition to the gate to turn
on and off the LX1971, a diode has been inserted to isolate the
LX1971 when it is shut down.
LED driver
controller or
dimming controller
input
Diable
control
Figure 1
CMOS
Gate
The example in figure one shows a fully automatic
lighting control solution with no user interaction. Choose
R1 and R2 values for any desired minimum brightness and
slope. Choose C1 to adjust response time. 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 represent the maximum. The first
step would be to determine the ratio of R1 and R2.
VDD
VSS
SNK
N/C
SRC
3.3V
60K
PWM
30K
10µF
30K
LED driver
controller or
dimming controller
input
R1 = R2 [ 3.0V/0.25V –1] = 11 * R2
R2 = [ 1.25V / 50uA ] = 25KΩ ∴ R1 = 11 * R2 = 275KΩ
The output node will actually reach 1.25V when the
source current from the LX1971 is only about 44uA since
about 6uA of current will be contributed from R1.
Copyright  2003
Rev. 1.0,2003-11-25
Figure 3
The preceding examples represent just a few of the many
ways the sensor can be used. For example since there is also a
complimentary sink output a resistor from VDD to SNK could
develop a voltage that could be compared (with some
hysteresis) to a fixed (or adjustable) reference voltage and
develop a logic signal. In the case of street lighting or
operation of shades such a signal would engage the function
when reaching the correct ambient light level.
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
APPLICATIONS
Next the value of R2 can be calculated based on the
maximum output source current coming from the LX1971
under the application’s maximum light exposure, lets say
this has been determined to be about 50uA . Thus R2 can
be calculated first order as follows:
LX1971
I N T E G R A T E D
Wide Range Visible Light Sensor
P R O D U C T S
P RODUCTION D ATA S HEET
ISRC STEP RESPONSE
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RESPONSE VS WAVELENGTH
Amplitude (µW/cm 2)
16
14
12
10
8
6
4
2
0
0
0.5
1
Tim e (Seconds)
1.5
2
VDD = 3.0V; RSRC = 25K & 4.7uF
LINE REGULATION
DARK CURRENT VS TEMP
22
1000
Dark Current (nA)
SRC Current (µA)
21.5
21
20.5
20
100
3V
5V
5.5V
10
19.5
1
-40
19
3
3.5
4
4.5
VDD (V)
5
5.5
-20
0
20
40
60
Temperature (ºC)
80
100
RSRC = 25K & 4.7uF
VDD = 3.5V; RSRC = 25K & 4.7uF
SNK OUTPUT PSRR
GAIN VS TEMP
70
1.15
y = 1.35E-03x + 9.64E-01
1.1
Gain/Gain(25ºC)
50
40
1.05
1
0.95
CHARTS
PSRR (db)
60
0.9
0.85
30
0.8
1
10
100
1000
10000
100000
Frequency (Hz)
0
50
Temperature (ºC)
100
VDD = 3.0V Direct Light Input of 13.14µW/cm2
VDD = 3.0V; RSNK = 25K & 4.7uF
Copyright  2003
Rev. 1.0,2003-11-25
-50
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
LX1971
I N T E G R A T E D
Wide Range Visible Light Sensor
P R O D U C T S
P RODUCTION D ATA S HEET
SNK COMPLIANCE VS CURRENT
SRC COMPLIANCE VS CURRENT
100
100
Output Current (µA)
Output Current (µA)
WWW . Microsemi .C OM
120
80
60
40
20
0
80
60
40
20
0
0.1
0.2
0.3
0.4
0.5
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Source Com pliance Voltage (VDD-SRC)
SNK com pliance Voltage (V)
VDD = 3.0V; RSNK = 25K & 4.7µF
VDD = 3.0V; RSRC = 25K & 4.7µF
SRC OUTPUT VS LUMINANCE(LUX)
SRC OUTPUT VS LUMINANCE(LUX)
160
50
Incandescent
Incandescent
40
SRC (uA)
SRC (uA)
120
80
30
20
40
10
0
0
0
3000
6000
9000 12000 15000
Luminance (lux)
18000
VDD = 4.0V; RSNK = 10K & 4.7µF
0
500
1000
1500
Luminance (lux)
2000
2500
VDD = 4.0V; RSNK = 10K & 4.7µ
CHARTS
Copyright  2003
Rev. 1.0,2003-11-25
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
LX1971
I N T E G R A T E D
Wide Range Visible Light Sensor
P R O D U C T S
P RODUCTION D ATA S HEET
PACKAGE DIMENSIONS
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DU
8-Pin Miniature Shrink Outline Package (MSOP)
A
MILLIMETERS
MIN
MAX
2.85
3.05
2.90
3.10
–
1.10
0.25
0.40
0.65 BSC
0.38
0.64
0.13
0.18
0.95 BSC
0.40
0.70
3°
0.05
0.15
4.75
5.05
INCHES
MIN
MAX
.112
.120
.114
.122
–
0.043
0.009
0.160
0.025 BSC
0.015
0.025
0.005
0.007
0.037 BSC
0.016
0.027
3°
0.002
0.006
0.187
0.198
MILLIMETERS
INCHES
A
a
B
C
1.22
0.85
0.60
0.60
0.048
0.033
0.024
0.024
P1
2.5
0.98
Dim
A
B
C
D
G
H
J
K
L
M
N
P
B
H
G
P
C
N
J
K
L
D
a
M
Active Area
Required Minimum Light footpri
Bonding / Wafer area
Dim
A
Active Area
C
B
C
L
Examination of
Active Area
Recommended light footprint pattern
Copyright  2003
Rev. 1.0,2003-11-25
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
MECHANICALS
P1
Note:
P1 represents a possible light footprint and its
dimensions are not subject to strict tolerances. Only
the active area of the device is required to be covered
with light. This larger footprint is designed to ensure
coverage of the device’s active area.
Page 8
LX1971
I N T E G R A T E D
Wide Range Visible Light Sensor
P R O D U C T S
P RODUCTION D ATA S HEET
WWW . Microsemi .C OM
NOTES
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.
Copyright  2003
Rev. 1.0,2003-11-25
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9