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LX1971
INTEGRATED PRODUCTS
Wide Range Visible Light Sensor
PRODUCTION DATA SHEET
DESCRIPTION
KEY FEATURES
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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.
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 5K to 50K 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.
Approximate Human Eye Spectral Response Low IR Sensitivity Highly Accurate & Repeatable Output Current vs. Light Square root transfer function Temperature Stable Integrated High Gain Photo Current Amplifiers Complementary Current Outputs No Optical Filters Needed BENIFITS * Requires no wavelength filters * Insensitive to UV and IR * More than 4 decades usable light range * Enables accurate lighting control systems
IMPORTANT: For the most current data, consult MICROSEMI's website: http://www.microsemi.com
PRODUCT HIGHLIGHT
VDD
4.7uF
VDD
25K
SNK
0.60V Typ
SNK
LX1971
SRC
4.7uF 25K
VOUT
0.45V Typ
SRC
GND
Ambient Light
LX1971 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
INTEGRATED PRODUCTS
Wide Range Visible Light Sensor
PRODUCTION DATA SHEET
ABSOLUTE MAXIMUM RATINGS 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 +85C Storage Temperature Range.............................................................................-55 to 125C Solder Reflow Peak Temperature (Soldering 10 seconds) ......................................... 240C
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. Solder reflow to follow: IPC/JEDEC J-STD-020B 7/02 Pb-SN Small Body Profile
PACKAGE PIN OUT
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VDD NC NC SRC
1 2 3 4
active area
8 7 6 5
VSS NC NC SNK
DU PACKAGE
(Top View)
8
1
1971
xxxx
7
2 3 4
THERMAL DATA
6 5
DU
Plastic MSOP 8-Pin 206C/W 39C/W
THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA THERMAL RESISTANCE-JUNCTION TO CASE, JC
DU PACKAGE
(Bottom View) xxxx = Denotes Date Code / Lot Information
FUNCTIONAL PIN DESCRIPTION NAME VDD VSS SNK SRC Input Supply Voltage Ground Reference for Power and Signal Output Output Current Sink Output Current Source DESCRIPTION
SIMPLIFIED BLOCK DIAGRAM
PACKAGE PHOTO
V DD SNK
PACKAGE DATA PACKAGE DATA
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
INTEGRATED PRODUCTS
Wide Range Visible Light Sensor
PRODUCTION DATA SHEET
RECOMMENDED OPERATING CONDITIONS Parameter
Supply Voltage (VDD ) SNK Compliance Voltage Range SRC Compliance Voltage Range SNK/SRC Output Resistor Range Outputs are functional down to VDD=2.7V
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Min
3 VSS +0.6 VSS 5
LX1971 Typ
Max
5.5 VDD VDD - 0.75 100
Units
V V V K
ELECTRICAL CHARACTERISTICS Unless otherwise specified, the following specifications apply over the operating ambient temperature -40C TA 85C, VDD = 3V to 5.5V, RLOAD= 25Kohms, Direct Light Input of 584W/cm2 except where otherwise noted. Performance between -40C and 0C and between 70C and 85C are assured by design and characterization. Parameter
Supply Voltage Range Input Supply Current
Symbol
VDD IDD ISRC ISRC
Test Conditions
Min
3
LX1971 Typ
Max
5.5
Units
VDC A A
VDD = 3.0V, ISRC = 62A, ISNK = open VDD = 3.0V, Direct Light Input of 2 584W/cm @ 25C VDD = 3.0V, Direct Light Input of 2 584W/cm VDD = 3.0V, Direct Light Input of 2 584W/cm VDD = 3.0V, Direct Light Input of 2 292W/cm VDD = 3.0V, Direct Light Input of 2 9.34W/cm VDD = 3.0V VDD = 3.0V, @ 95% of nominal output current VDD = 3.0V, @ 95% of nominal output current VDD = 3V, No Light, 25C VDD = 3V, No Light, -40C to 70C VDD = 3V, No Light, 85C VDD = 5.5V, No Light, 25C
350 55 52 -70 34 5.5
590 61 61 -61 41 7 2 VSS +0.45 VDD - 0.6 150 450 550 320 520 60
750 67 70 -52 48 8.5 6 VSS +0.6 VDD - 0.7 400 1000 1150
Output Current
ISNK ISRC ISRC
A A A % V V nA nA nA nA
Output SNK/SRC Current Matching SNK Minimum Compliance Voltage SRC Maximum Compliance Voltage SNK/SRC Output Dark Current SNK/SRC Output Dark Current SNK/SRC Output Dark Current SNK/SRC Output Dark Current Wavelength of Peak Sensitivity Half Reception Angle Supply Voltage Coefficient of Output Current Resolution Limit Due To Random Noise Sensitivity Change @ 910nm Radiant Sensitive Area
IMATCH SNKVMIN SRCVMAX IDARK3.0V IDARK3.0V IDARK3.0V IDARK5.5V PS 1/2 PSRR IMIN ISRC IR A
E ELECTRICALS
nm deg 3.5 %/V nW/cm 10
2
VDD = 3V to 5.5V Minimum usable resolution Current responsivity change with 2 additional direct light input of 584W/cm at 910nm, TA = 25C, VDD = 3V Photodiode Area -10
2.9 146 0 .369
2
% of peak mm
2
The input irradiance is supplied from a white light-emitting diode (LED) optical source adjusted to impose 584W/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
LX1971
INTEGRATED PRODUCTS
Wide Range Visible Light Sensor
PRODUCTION DATA SHEET
APPLICATION INFORMATION
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SRC Current (A)
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. 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.
LX1971 Calculated SRC Full Range Response
250 200 150 100 50 0 0 5000 10000 15000 20000 25000 Incandescent Light (lux)
I OUT =
20000 lux
(
L x .808 + 1.1A for L < 2500 lux
)
<2500 Lux Formula >2500 Lux Formula
I OUT = (L x .0083A) + 23A for 2500 lux < L <
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. 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. 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.
LX1971 Calculated SRC Low Level Response
50 SRC Current (A) 40 30 20 10 0 0 500 1000 1500 2000 2500 Incandescent Light (lux)
<2500 Lux Formula
LX1971 Calculated SRC High Level Response
250 SRC Current (A)
APPLICATIONS APPLICATIONS
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
INTEGRATED PRODUCTS
Wide Range Visible Light Sensor
PRODUCTION DATA SHEET
APPLICATION EXAMPLES
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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.
3.3V or 5V VDD VSS SNK N/C LED driver controller or dimming controller input SRC 3V
R1 R2 C1 10F
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 VSS SNK N/C LED driver controller or dimming controller input 10F SRC
3.3V PWM
R1 40K R2 25K
Figure 2
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.
Diable control CMOS Gate VDD VSS SNK N/C SRC 3.3V
60K
Figure 1
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.
R1 = R2 [ 3.0V/0.25V -1] = 11 * R2
PWM
30K 10F 30K
LED driver controller or dimming controller input
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:
R2 = [ 1.25V / 50uA ] = 25K R1 = 11 * R2 = 275K
Figure 3
APPLICATIONS APPLICATIONS
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.
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.
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 5
LX1971
INTEGRATED PRODUCTS
Wide Range Visible Light Sensor
PRODUCTION DATA SHEET
RESPONSE VS WAVELENGTH
16 Amplitude (W/cm 2) 14 12 10 8 6 4 2 0 0
ISRC STEP RESPONSE
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0.5
1 Tim e (Seconds)
1.5
2
VDD = 3.0V; RSRC = 25K & 4.7uF
LINE REGULATION
22 21.5 SRC Current (A) 21 20.5 20 19.5 19 3 3.5 4 4.5 VDD (V) 5 5.5
1000 Dark Current (nA)
DARK CURRENT VS TEMP
100 3V 5V 5.5V
10
1 -40
-20
0
20 40 60 Temperature (C)
80
100
VDD = 3.5V; RSRC = 25K & 4.7uF
RSRC = 25K & 4.7uF
SNK OUTPUT PSRR
70
GAIN VS TEMP
1.15 1.1 Gain/Gain(25C)
y = 1.35E-03x + 9.64E-01
60 PSRR (db)
1.05 1 0.95 0.9 0.85
50 40
CHARTS CHARTS
30 1 10 100 1000 10000 100000 Frequency (Hz)
VDD = 3.0V; RSNK = 25K & 4.7uF
0.8 -50 0 50 Temperature (C)
VDD = 3.0V Direct Light Input of 13.14W/cm2
100
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 6
LX1971
INTEGRATED PRODUCTS
Wide Range Visible Light Sensor
PRODUCTION DATA SHEET
SNK COMPLIANCE VS CURRENT
120 Output Current (A)
SRC COMPLIANCE VS CURRENT
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100 Output Current (A)
0.1 0.2 0.3 0.4 0.5
100 80 60 40 20 0 SNK com pliance Voltage (V)
VDD = 3.0V; RSNK = 25K & 4.7F
80 60 40 20 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Source Com pliance Voltage (VDD-SRC)
VDD = 3.0V; RSRC = 25K & 4.7F
SRC OUTPUT VS LUMINANCE(LUX)
160
Incandescent
SRC OUTPUT VS LUMINANCE(LUX)
50
Incandescent
120 SRC (uA) SRC (uA) 0 3000 6000 9000 12000 15000 Luminance (lux) 18000
40 30 20 10
80
40
0
0 0 500 1000 1500 Luminance (lux) 2000 2500
VDD = 4.0V; RSNK = 10K & 4.7F
VDD = 4.0V; RSNK = 10K & 4.7
C 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
INTEGRATED PRODUCTS
Wide Range Visible Light Sensor
PRODUCTION DATA SHEET
PACKAGE DIMENSIONS
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DU
8-Pin Miniature Shrink Outline Package (MSOP)
A
Dim A B C D G H J K L M N P 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
B
H
G P C N D L K J M
a
Active Area Required Minimum Light footpri Bonding / Wafer area
A C
Dim
Active Area
MILLIMETERS 1.22 0.85 0.60 0.60 2.5
INCHES 0.048 0.033 0.024 0.024 0.98
B
C L
Examination of Active Area
A a B C P1
Recommended light footprint pattern
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.
M MECHANICALS
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 8
LX1971
INTEGRATED PRODUCTS
Wide Range Visible Light Sensor
PRODUCTION DATA SHEET
NOTES
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N 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

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