LX1970 I N T E G R A T E D Visible Light Sensor P R O D U C T S P RODUCTION D ATA S HEET KEY FEATURES DESCRIPTION Photo current is multiplied by integrated high gain amplifiers and is 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 10KΩ to 50KΩ range. With accurate internal gain amplifiers, design complexity and cost are greatly reduced. The LX1970 is available in the 8-pin MSOP. IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com Protected By U.S. Patents: 6,787,757; Patents Pending Approximate Human Eye Spectral Response Low IR Sensitivity Highly Accurate & Repeatable Output Current vs. Light Voltage Scalable Temperature Stable Integrated High Gain Photo Current Amplifiers Complementary Current Outputs No Optical Filters Needed WWW . Microsemi .C OM The LX1970 is a new technology light sensor with spectral response that emulates the human eye. This device is ideal for monitoring ambient light for brightness control systems in flat panel displays. It has a unique photo diode arrangement (patents pending) with a peak response at 520 nm while sharply attenuating both ultra violet and infrared wavelengths. The photo sensor is a PIN diode array with an accurate, linear, and very repeatable current transfer function. APPLICATIONS PDA Notebook PC LCD TV Tablet PC Cell phones PRODUCT HIGHLIGHT V DD 4.7uF V DD 50K I SNK LX1970 SNK 0.3V T yp V OUT SRC 4.7uF I 50K G ND 0.3V T YP SRC LX1970 Am bient Light PACKAGE ORDER INFO Plastic MSOP DU 8-Pin TA (°C) RoHS Compliant / Pb-free -40 to 85 LX1970IDU Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1970IDU-TR) Copyright © 2007 Rev. 1.5b, 2008-01-25 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1970 I N T E G R A T E D 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.......................................................................... -40 to +100°C Solder Reflow Peak Temperature (40 seconds maximum exposure) ............260°C (+0, -5) 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. DU PACKAGE (Top View) 1 8 5 THERMAL DATA DU 1970 6 xxxx 7 WWW . Microsemi .C OM ABSOLUTE MAXIMUM RATINGS 2 3 4 DU PACKAGE Plastic MSOP 8-Pin (Bottom View) THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 206°C/W 39°C/W THERMAL RESISTANCE-JUNCTION TO CASE, θJC xxxx = Denotes Date Code / Lot Information RoHS / Pb-free NiPdAu Pin Finish MSL 2 / 260°C / 1 Year 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 © 2007 Rev. 1.5b, 2008-01-25 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 LX1970 I N T E G R A T E D Visible Light Sensor P R O D U C T S P RODUCTION D ATA S HEET RECOMMENDED OPERATING CONDITIONS LX1970 Typ Min Supply Voltage (VDD ) Max WWW . Microsemi .C OM Parameter Units 2¹ 5.5 V SNK Compliance Voltage Range VSS +0.5 VDD V SRC Compliance Voltage Range VSS VDD - 0.5 V SNK/SRC Output Resistor Range 10 1000 KΩ Note 1: SRC output will work down to VDD=1.8V ELECTRICAL CHARACTERISTICS Unless otherwise specified, the following specifications apply over the operating ambient temperature -40°C ≤ TA ≤ 85°C, VDD = 2V to 5.5V, RLOAD= 50Kohms, Direct Light Input² of 14.6µW/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 Test Conditions Min Supply Voltage Range VDD Input Supply Current IDD VDD = 3.0V, ISRC = 38µA, ISNK= open 60 ISRC VDD = 3.0V ISNK VDD = 3.0V Output SNK/SRC Current Matching IMATCH VDD = 3.0V SNK Minimum Compliance Voltage SNKVMIN SRC Maximum Compliance Voltage SRCVMAX Output Current LX1970 Typ 2 Max Units 5.5 VDC 85 110 µA 30 38 46 µA -30 -38 -46 µA 0.5 2 % VDD = 3.0V, @ 95% of nominal output current VSS +0.3 VSS +0.5 V VDD = 3.0V, @ 95% of nominal output current VDD – 0.3 VDD – 0.5 V 10 300 nA 3 SNK/SRC Output Dark Current IDARK Wavelength of Peak Sensitivity λPS 520 nm Half Reception Angle θ½ ±60 deg Sensitivity @ 540nm (peak) Sensitivity Change @ 910nm Radiant Sensitive Area 4 PSRR VDD = 2V to 5.5V 2.2 Irradiance current responsivity 2.6 Current responsivity change with 2 additional direct light input of 14.6µW/cm at 910nm Photodiode area -5 5 %/V 2 A/(W/cm ) 0 5 0.369 % of peak mm 2 2 Note 2: The input irradiance is supplied from a white light-emitting diode (LED) optical source adjusted to impose 14.6µW/cm at 555nm on the sensor’s surface. Note 3: See Figure 1 Note 4: See Figure 2 Copyright © 2007 Rev. 1.5b, 2008-01-25 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 ELECTRICALS Supply Voltage Coefficient of Output Current VDD = 5.5V, No Light LX1970 I N T E G R A T E D Visible Light Sensor P R O D U C T S P RODUCTION D ATA S HEET VS VDD VDD Current Sources A Current Source ISNK LX1970 LX1970 White LED ISRC % IR LED 910nm White LED SRC A A Figure 1 – Light Current Measurement Circuit WWW . Microsemi .C OM MEASUREMENT CIRCUIT CONFIGURATIONS Figure 2 – IR sensitivity Measurement Circuit APPLICATION NOTES LIGHT UNITS 2 Copyright © 2007 Rev. 1.5b, 2008-01-25 If the photo sensor had a truly photopic response, it would produce the same output current for the same number of nits or 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 LX1970 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. Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4 APPLICATIONS In converting from µW/cm to Nits it is necessary to define the light source. Nits are units for a measurement of luminance, which is the apparent brightness of an illuminated flat surface. 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. At 555nm, the conversion factor is 683 Lux = 1W/m2 = 100µW/cm2. Therefore 14.6µW/cm² = 100 lux at 555nm. The next step in the conversion process is to convert illuminance to luminance. The units for illuminance are lux or lumens/m2. The units for luminance are Nits or lumens/m2/steradian. Assuming the illuminance falls on a Lambertian surface which has perfect dispersion and total reflection, the conversion from lux to nits is 3.14 lux falling on a Lambertian reflector produces 1 Nit. Therefore 100 Lux will produce 31.4 Nits. LX1970 I N T E G R A T E D Visible Light Sensor P R O D U C T S P RODUCTION D ATA S HEET APPLICATION INFORMATION 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 1200 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. SRC Current (µA) I OUT = L × 0.76µA for L < 1200 lux LX1970 Calculated SRC Full Range Response 700 600 500 400 300 200 100 0 0 200 400 600 800 1000 1200 Light (lux) LX1970 SRC Actual SRC with 10K Resistor 450 400 350 300 250 200 150 100 50 0 0 200 400 600 800 1000 1200 Light (lux) Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 APPLICATIONS The first curve shows the calculated responsiveness of the LX1970 without load resistors based on the formula above. It 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-350mV @ about 100 lux. The second curve shows saturation of the output with VIN = 5V and a 10K resistor SRC to ground, above about 300uA the output becomes non-linear as it begins to saturate. Copyright © 2007 Rev. 1.5b, 2008-01-25 1000 900 800 SRC Current (µA) The LX1970 has a responsiveness that is directly proportional to the intensity of light falling on the photo receptors. Although the gain varies depending on the wavelength of the light and the direction of light, in general for a 555nm wavelength (yellow-green), the sensitivity is: WWW . Microsemi .C OM The LX1970 is a light sensor with a spectral response that resembles the human visual system. It is packaged in clear MSOP package. Microsemi also offers the LX1971 with the same pin out and similar supply voltage range as 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. Page 5 LX1970 I N T E G R A T E D Visible Light Sensor P R O D U C T S P RODUCTION D ATA S HEET APPLICATION EXAMPLES The output node will actually reach 1.25V when the source current from the LX1970 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 3 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 WWW . Microsemi .C OM 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 LX1970 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 and LX1993. In each specific application it is important to recognize the need to correlate the sink and source current of the LX1970 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 LX1970 for a given exposure of light. VDD VSS N/C SNK SRC To inverter brightness input or LED driver 10µF controller input. 3.3V PW M R1 40K 3.3V or 5V R2 25K VDD VSS SNK N/C Figure 3 Figure 4 shows how a fully manual override can be quickly added to the example in figure 3. In addition to the gate to turn on and off the LX1970, a diode has been inserted to isolate the LX1970 when it is shut down. SRC To inverter brightness input or LED driver controller. C1 3V R1 R2 10µF Diable control Figure 2 The example in figure 2 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 and 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. Copyright © 2007 Rev. 1.5b, 2008-01-25 VDD VSS SNK N/C SRC 3.3V 60K PW M 30K 10µF 30K To inverter brightness input or LED driver controller. Figure 4 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 reference voltage and develop a logic shutdown signal. If the application is utilizing a transflective or reflective LCD display such a signal could disable the backlight or front light to the display when reaching sufficient ambient light. Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 APPLICATIONS ⎤ ⎡ 3.0V − 1⎥ = 11 × R2 ⎣ 0.25V ⎦ Next the value of R2 can be calculated based on the maximum output source current coming from the LX1970 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: ⎡1.25V ⎤ R2 = ⎢ = 25KΩ ∴ R1 = 11 × R2 = 275KΩ ⎣ 50µA ⎥⎦ R1 = R2 ⎢ CMO S Gate LX1970 I N T E G R A T E D Visible Light Sensor P R O D U C T S P RODUCTION D ATA S HEET RESPONSE VS WAVELENGTH ISNK STEP RESPONSE WWW . Microsemi .C OM 16 Amplitude (µW/cm2) 14 12 10 8 6 4 2 0 0 0.5 1 T im e ( S e c o nds ) Load = 10kΩ and 1µF Photo Step = Direct Light Input of 14.6µW/cm2 SMALL SIGNAL FREQUENCY RESPONSE 0.73µW/cm2 2.63µW/cm2 13.14µW/cm2 0 Dark Current (nA) -5 -10 Amplitude (dB) DARK CURRENT VS TEMP -15 -20 -25 -30 -35 -40 1000 VDD=5.5V 100 VDD=1.8V 10 1 0.1 -45 0.01 10 100 1000 10000 100000 25 Frequency (Hz) 40 55 70 85 Temperature (ºC) VDD = 3.0V, SNK , Three Light Levels, No Filtering GAIN VS TEMP 1.15 0.00 1.1 -20.00 1.05 Gain/Gain(25ºC) 20.00 -40.00 -60.00 2.63µW/cm2 -80.00 y = 1.35E-03x + 9.64E-01 1 0.95 CHARTS Amplitude (dB) SNK OUTPUT PSRR 0.9 13.14µW/cm2 -100.00 0.85 -120.00 1 10 100 1000 10000 100000 Frequency (Hz) 0 50 100 Temperature (ºC) VDD = 3.0V Load = 10kΩ and 1µF to Ground Copyright © 2007 Rev. 1.5b, 2008-01-25 0.8 -50 VDD = 3.0V Direct Light Input of 13.14µW/cm2 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 LX1970 I N T E G R A T E D Visible Light Sensor P R O D U C T S P RODUCTION D ATA S HEET VERTICAL DIRECTION RESPONSE HORIZONTAL DIRECTION RESPONSE WWW . Microsemi .C OM 1 1 SRC COMPLIANCE VS CURRENT 140 140 120 120 Output Current (µA) Output Current (µA) SNK COMPLIANCE VS CURRENT 100 80 60 40 20 100 80 60 40 20 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.1 SNK compliance Voltage (V) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Source Compliance Voltage (VDD-SRC) VDD = 3.0V VDD = 3.0V SRC CURRENT VS LIGHT (LUX) TYPICAL LOW AMBIENT RESPONSE 1.200 Output Current (µA) cool w hite Incandescent 200 100 1.000 0.800 0.600 0.400 0.200 0.000 0 0 100 200 300 0 0.2 0.6 0.8 1 Am bient Light (lux) Light Input (LUX) 8 5 °C VDD = 5.0V; SRC = 10K & 4.7µF to GND Copyright © 2007 Rev. 1.5b, 2008-01-25 0.4 7 5 °C 5 5 °C <2 5 °C 5V Input Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8 CHARTS SRC Current (µA) 300 LX1970 I N T E G R A T E D Visible Light Sensor P R O D U C T S P RODUCTION D ATA S HEET DU WWW . Microsemi .C OM PACKAGE DIMENSIONS 8-Pin Miniature Shrink Outline Package (MSOP) D Top View Dim E1 S e E A A1 c L1 L b Θ A A1 b c D e E E1 L L1 S Θ MILLIMETERS MIN MAX – 1.10 0.05 0.15 0.26 0.41 0.13 0.23 2.90 3.10 0.65 BSC 4.75 5.05 2.90 3.10 0.41 0.71 0.95 BSC 0.525 BSC 3° INCHES MIN MAX – 0.043 0.002 0.006 0.010 0.016 0.005 0.009 0.114 0.122 0.025 BSC 0.187 0.198 0.114 0.122 0.016 0.028 0.037 BSC 0.021 BSC 3° Side Views MILLIMETERS INCHES A B C D 0.225 0.145 0.600 0.612 0.0088 0.0057 0.0236 0.0241 P1 2.5 0.98 Dim Active Area Required Minimum Light footprint Bonding / Wafer area B Active Area A CL C D CL Note: CL is the center of the package 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. Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 MECHANICALS Copyright © 2007 Rev. 1.5b, 2008-01-25 P1 Examination of Active Area Page 9 LX1970 I N T E G R A T E D 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 © 2007 Rev. 1.5b, 2008-01-25 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 10