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LX1972A
TM (R)
Ambient Light Detector
PRODUCTION DATA SHEET
DESCRIPTION
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
The LX1972A is a low cost silicon light sensor with a spectral response that closely emulates the human eye. Patented circuitry produces peak spectral response at 580nm, with an IR response less than 5% of the peak response, above 900nm. The photo sensor is a PIN diode array with Microsemi's Best EyeTM processing that provides a nearly perfect photopic light wavelength response curve. LX1972A provides 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 5K to 100K) and the power supply values. Typically the LX1972A needs only 2.7V 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 (-40C to +85C), providing high accuracy at low light levels. Usable ambient light conditions range is from 1 to more than 5000 Lux. The LX1972A is optimized for controlling back lighting systems in low cost consumer products such as LCD TV, portable computers, and digital cameras.
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Portable Electronic Displays LCD TV Backlight Systems Digital Still Cameras (DSC) Desk Top Monitors Notebook Computers
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
1.7V Typical @ 100 Lux
LX1972A VSS VSS
Ambient Light
PACKAGE ORDER INFO
LX1972A
LX1972A LX1972A
TA (C) -40 to 85
BC
Plastic 1206 2-Pin LX1972AIBC
RoHS Compliant / Pb-free
Note: Available in Tape & Reel. Append the letters "TR" to the part number. (i.e. LX1972AIBC-TR)
Copyright (c) 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
LX1972A
TM (R)
Ambient Light Detector
PRODUCTION DATA SHEET
ABSOLUTE MAXIMUM RATINGS
PACKAGE PIN OUT
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Supply Input Voltage ...........................................................................-0.3V to 6V Ground Current ..........................................................................Internally Limited Operating Temperature Range .........................................................-40C to 85C Maximum Operating Junction Temperature ................................................ 150C Storage Temperature Range.........................................................-40C to +100C Peak Package Solder Reflow Temp. (40 second max. exposure) ... 260C (+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.
VDD
1 2
VSS
BC PACKAGE
(Top View)
RoHS / Pb-free Gold Lead Finish
THERMAL DATA
BC
Plastic 1206 2-Pin 850C/W
THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA
Junction Temperature Calculation: TJ = TA + (PD x JA). The JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow.
FUNCTIONAL PIN DESCRIPTION Name Description Positive Terminal Negative Terminal
VDD VSS
P D PACKAGE DATA
Copyright (c) 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 2
LX1972A
TM (R)
Ambient Light Detector
PRODUCTION DATA SHEET
CHARACTERISTIC CURVES
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1.2 Normalized Diode Response 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 400 600 800 Wavelength (nm) 1000
Minimum VDD Voltage
LX1972A Human Eye
4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 -40 @ 1000 Lux & 5k Load Resistor @ 100 Lux & 5k Load Resistor -20 0 20 40 Temperature (C) 60 80
Chart 1 - Response vs. Wavelength
IOUT vs Temperature @ 10, 100 Lux
25.00
400 350
Chart 2 -Minimum VDD Voltage vs. Temperature
20.00 IOUT @ 100 Lux
ID (nA)
300 250 200 150 100
IOUT (A)
15.00
IOUT @ 10 Lux
10.00
5.00
50 0 -40
0.00 -40
-20
0
20
40
60
80
-20
0
20
40
60
80
100
Temperature (C)
Temperature (C)
Chart 3 - IOUT vs. Temperature
Chart 4 - Dark Current vs. Temperature
C CHARTS
Copyright (c) 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 3
LX1972A
TM (R)
Ambient Light Detector
PRODUCTION DATA SHEET
The following specifications apply over the operating ambient temperature -40C TA the following test conditions: See Note 1, VDD =5V, Rload = 5K Parameter
RESPONSE
ELECTRICAL CHARACTERISTICS
85C except where otherwise noted and with
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Symbol PR
Test Conditions
Min
LX1972A Typ Max 580
Units nm
Peak Spectral Response Infrared Response Minimum Operational Voltage
IDD ( ) IDD ( PR )
VDD-VSS
EV(white) = 1000 Lux, EV(810nm) = 146W/cm, Note 3 EV = 100 Lux EV = 1000 Lux EV = 2000 Lux EV = 10 Lux, Note 2 EV = 100 Lux, Note 2 EV = 1000 Lux, Note 2 EV = 2000 Lux, Note 2; 10 Lux EV 1000 Lux EV = 0 Lux, TA = 25C EV = 0 Lux VRIPPLE = 10mVP-P, f = 10kHz
-5
1 1.4 2.2 2.8 2.4 24 235 470 2 -25 0.04
5 2 2.7 3 3 30 294 587 15 50 200
% V
Light Current Gain Linearity Dark Current Power Supply Rejection Ratio Radiant Sensitive Area
ISS
1.8 18 176 353 -15
A % nA dB mm2
IDD(DARK) PSRR
Notes: 1. The input irradiance (EV) is supplied from a white light-emitting diode (LED) optical source. 2. See Figure 1. 3. See Figure 2.
TEST CIRCUITS
VDD
VDD
LX1972A Part
White LED
LX1972A Part
White LED 810nm
VSS
5K
VSS 5K
Figure 1 - Operational Voltage Measurement Circuit
Figure 2 - IR Sensitivity Measurement Circuit
ELECTRICALS ELECTRICALS
Copyright (c) 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 4
LX1972A
TM (R)
Ambient Light Detector
PRODUCTION DATA SHEET
SIMPLIFIED BLOCK DIAGRAM
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LX1972A
VDD
Current Amp
VSS
Figure 3 - Simplified Block Diagram
APPLICATION NOTE
LIGHT UNITS In converting from W/cm 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 W/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 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/m2 = 100W/cm2. Therefore 14.6W/cm2 = 100 lux at 555nm.
2
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.
APPLICATIONS APPLICATIONS
Copyright (c) 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
LX1972A
TM (R)
Ambient Light Detector
PRODUCTION DATA SHEET
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 LX1972A can be used to control the brightness input of CCFL inverters (like Microsemi's PanelMatchTM 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 LX1972A 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 LX1972A for a given exposure of light.
3.3V or 5V VDD Part VSS 3.3V
R1 R2
The output node will actually reach 1.25V when the source current from the LX1972A is only about 43A, since about 7A 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.
3.3V or 5V VDD Part VSS
3.3V PWM
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R1 40K
R2 25K
To inverter brightness input or LED driver 10F controller input.
Figure 5
To inverter brightness input or LED driver controller.
C1 10F
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 LX1972A, a diode has been inserted to isolate the sensor when it is disabled.
Disable control CMOS Gate VDD Part VSS
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.
R2 x 3.3 = 0.25 R1+ R2 R1= R2
3.3V 0.25V
3.3V
PWM
30K
60K
10F
30K
To inverter brightness input or LED driver controller.
A APPLICATIONS
-1 = 12.2xR2
Next, the value of R2 can be calculated based on the maximum output source current coming from the LX1972A under the application's maximum light exposure, lets say this has been determined to be about 50A . Thus R2 can be calculated first order as follows:
R2 =
1.25V = 25k 50A
Figure 6
R1 = 12.2 x R2 = 305k
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 www.microsemi.com. Although this application note is written around Microsemi's LX1970 visible light sensor, the circuits can be easily adapted for use with the LX1972A.
Copyright (c) 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 6
LX1972A
TM (R)
Ambient Light Detector
PRODUCTION DATA SHEET
APPLICATION CIRCUITS
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L1 10H
D1 UPS5817
VIN
R1 100K
LX1995
IN
C1 4.7F
BACKLIGHT
GND
SW FB
C2 1F
SHDN GND
SHDN
R4 10K MMBT2907 R8 60.4K C3 10F R10 49.9K
R5 5.76K R6 15
R7 24.9K
3.3V
LX1972A
VSS VDD
C4 0.1F
Figure 7 - Typical Application with Microsemi's LX1995 LED Driver IC
22H VIN = 2.0V to 5.5V FDN337 PWM Dimming Input
UPS5819
1M
1F
VIN
4.99K
DRV SRC OVP FB CMP
0.1F 41.2K 15
S/P BRT LS GND
3.3V
LX1972A
VDD VSS
MMBT2907
15K
22F 100K 178K
1F
LX1994
APPLICATIONS APPLICATIONS
Figure 8 - Typical Application with Microsemi's LX1994 LED driver IC
Copyright (c) 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 7
LX1972A
TM (R)
Ambient Light Detector
PRODUCTION DATA SHEET
PACKAGE DIMENSIONS
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BC
2-Pin 1206 Standard Carrier
D
CL
Sensor Active Area: 0.2 x 0.2mm
2
P
C
0.03
CL C
R
1
2
Top E
0.19 - 0.25mm
Sensor Active Area
A Side
B
1
Dim A B D E H M P R X
MILLIMETERS MIN MAX 0.95 1.25 0.40 0.70 3.05 3.35 1.85 2.15 0.40 0.60 3 nom 1.45 1.75 0.25 nom 0.02 0.05
INCHES MIN MAX 0.037 0.049 0.016 0.028 0.120 0.132 0.073 0.085 0.016 0.024 3 nom 0.057 0.069 0.010 nom
0.0008 0.002
Bottom H X
Pin 1 Indicator (top side) / Alignment Indicator (Bottom side)
Note: Dimensions do not include protrusions; these shall not exceed 0.155mm (.006") on any side.
1.50mm
0.06in.
Recommended Soldering Pattern for reflow soldering of the BC (1206) package.
1.50mm 2.0mm
0.06in.
1.50mm
0.06in.
0.08in.
Super Imposed 1206 Package
Basic specification is < 5 seconds @ 260C when applying solder.
4.00 1.75
Lead In: 10 min empty Loaded: 3000 pcs Lead Out: 40 min empty
5.25 8.00 2.00
MECHANICALS MECHANICALS
0.20
4.00
1.30
Copyright (c) 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 8
LX1972A
TM (R)
Ambient Light Detector
PRODUCTION DATA SHEET
NOTES
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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 (c) 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
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