LX1970

LX1970 INTEGRATED PRODUCTS Visible Light Sensor P RODUCTION D ATA S HEET DESCRIPTION KEY FEATURES W WW . 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. 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. 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 APPLICATIONS PDA Notebook PC LCD TV Tablet PC Cell phones 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 V DD 4.7uF V DD 50K SNK I V OUT S NK 0.3V T yp LX1970 SRC 4.7uF 50K I G ND 0.3V T YP S RC Am bient Light LX1970 LX1970 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 © 2002 Rev. 1.4b, 2005-08-10 Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1970 INTEGRATED PRODUCTS Visible Light Sensor P RODUCTION D ATA S HEET 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 +85°C Storage Temperature Range.......................................................................... -40 to +100°C Solder Reflow Peak Temperature (Soldering 10 seconds) ......................................... 240°C 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 Sn-Pb Small Body Profile VDD NC NC SRC PACKAGE PIN OUT 1 2 3 4 8 7 6 5 VSS NC NC SNK W WW . Microsemi . C OM DU PACKAGE (Top View) 8 1 1970 xxxx 7 6 2 3 4 THERMAL DATA 5 DU Plastic MSOP 8-Pin 206°C/W 39°C/W DU PACKAGE (Bottom View) xxxx = Denotes Date Code / Lot Information RoHS / Pb-free Gold Lead Finish MSL 2 / 260°C / 1 Year THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA THERMAL RESISTANCE-JUNCTION TO CASE, θJC 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 PACKAGE DATA PACKAGE DATA SNK SRC V SS Copyright © 2002 Rev. 1.4b, 2005-08-10 Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 LX1970 INTEGRATED PRODUCTS Visible Light Sensor P RODUCTION D ATA S HEET RECOMMENDED OPERATING CONDITIONS W WW . Microsemi . C OM Parameter Supply Voltage (VDD ) SNK Compliance Voltage Range SRC Compliance Voltage Range SNK/SRC Output Resistor Range Note 1: SRC output will work down to VDD=1.8V Min 2¹ VSS +0.5 VSS 10 LX1970 Typ Max 5.5 VDD VDD - 0.5 1000 Units V V V KΩ 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 Supply Voltage Range Input Supply Current Symbol VDD IDD ISRC Test Conditions Min 2 LX1970 Typ Max 5.5 Units VDC µA µA µA % V V nA nm deg VDD = 3.0V, ISRC = 38µA, ISNK= open VDD = 3.0V VDD = 3.0V VDD = 3.0V VDD = 3.0V, @ 95% of nominal output current VDD = 3.0V, @ 95% of nominal output current VDD = 5.5V, No Light 60 30 -30 85 38 -38 0.5 VSS +0.3 VDD – 0.3 10 520 ±60 110 46 -46 2 VSS +0.5 VDD – 0.5 300 Output Current 3 ISNK Output SNK/SRC Current Matching SNK Minimum Compliance Voltage SRC Maximum Compliance Voltage SNK/SRC Output Dark Current Wavelength of Peak Sensitivity Half Reception Angle Supply Voltage Coefficient of Output Current Sensitivity @ 540nm (peak) Sensitivity Change @ 910nm Radiant Sensitive Area 4 IMATCH SNKVMIN SRCVMAX IDARK λPS θ½ PSRR VDD = 2V to 5.5V Irradiance current responsivity Current responsivity change with 2 additional direct light input of 14.6µW/cm at 910nm Photodiode area -5 2.2 2.6 0 0.369 2 5 %/V ELECTRICALS ELECTRICALS A/(W/cm ) 5 % 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 © 2002 Rev. 1.4b, 2005-08-10 Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX1970 INTEGRATED PRODUCTS Visible Light Sensor P RODUCTION D ATA S HEET MEASUREMENT CIRCUIT CONFIGURATIONS VS VDD Current Source LX1970 White LED A ISRC A ISNK LX1970 White LED IR LED 910nm A % SRC Current Sources VDD W WW . Microsemi . C OM Figure 1 – Light Current Measurement Circuit Figure 2 – IR sensitivity Measurement Circuit APPLICATION NOTES LIGHT UNITS 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. 2 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. 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. APPLICATIONS APPLICATIONS Copyright © 2002 Rev. 1.4b, 2005-08-10 Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4 LX1970 INTEGRATED PRODUCTS Visible Light Sensor P RODUCTION D ATA S HEET APPLICATION INFORMATION W WW . 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. 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: LX1970 Calculated SRC Full Range Response 1000 900 800 700 600 500 400 300 200 100 0 0 200 400 600 800 1000 1200 I OUT = L × 0.76µA for L < 1200 lux 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. 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. SRC Current (µA) Light (lux) LX1970 SRC Actual SRC with 10K Resistor 450 400 SRC Current (µA) 350 300 250 200 150 100 50 0 0 200 400 600 800 1000 1200 Light (lux) APPLICATIONS APPLICATIONS Copyright © 2002 Rev. 1.4b, 2005-08-10 Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX1970 INTEGRATED PRODUCTS Visible Light Sensor P RODUCTION D ATA S HEET APPLICATION EXAMPLES W WW . 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. 3.3V or 5V VDD VSS SNK N/C SRC 3V R1 R2 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 VDD VSS SNK N/C To inverter brightness input or LED driver 10µF controller input. SRC 3.3V PW M R1 40K R2 25K To inverter brightness input or LED driver controller. C1 10µF 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. Diable control CMO S Gate VDD VSS SNK N/C SRC 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. ⎤ ⎡ 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 ⎢ 3.3V 60K PW M 3 0K 10µF 30K To inverter brightness input or LED driver controller. A APPLICATIONS 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. Page 6 Copyright © 2002 Rev. 1.4b, 2005-08-10 Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 LX1970 INTEGRATED PRODUCTS Visible Light Sensor P RODUCTION D ATA S HEET RESPONSE VS WAVELENGTH 16 14 2 Amplitude (µW/cm ) ISNK STEP RESPONSE W WW . Microsemi . C OM 12 10 8 6 4 2 0 0 0.5 T im e ( S e c o nds ) 1 Load = 10kΩ and 1µF Photo Step = Direct Light Input of 14.6µW/cm2 SMALL SIGNAL FREQUENCY RESPONSE 0 -5 -10 Amplitude (dB) 0.73µW/cm2 2.63µW/cm2 13.14µW/cm2 Dark Current (nA) DARK CURRENT VS TEMP 1000 100 10 1 0.1 0.01 VDD=5.5V VDD=1.8V -15 -20 -25 -30 -35 -40 - 45 10 100 1000 Frequency (Hz) 10000 100000 25 40 55 Temperature (ºC) 70 85 VDD = 3.0V, SNK , Three Light Levels, No Filtering SNK OUTPUT PSRR 20.00 0.00 Amplitude (dB) Gain/Gain(25ºC) GAIN VS TEMP 1.15 1.1 1.05 1 0.95 y = 1.35E-03x + 9.64E-01 -20.00 -40.00 -60.00 -80.00 -100.00 - 120.00 1 10 100 1000 10000 100000 Frequency (Hz) VDD = 3.0V Load = 10kΩ and 1µF to Ground 2.63µW/cm2 13.14µW/cm2 CHARTS CHARTS 0.9 0.85 0.8 -50 0 50 Temperature (ºC) 100 VDD = 3.0V Direct Light Input of 13.14µW/cm2 Copyright © 2002 Rev. 1.4b, 2005-08-10 Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 LX1970 INTEGRATED PRODUCTS Visible Light Sensor P RODUCTION D ATA S HEET VERTICAL DIRECTION RESPONSE HORIZONTAL DIRECTION RESPONSE W WW . Microsemi . C OM 1 1 SNK COMPLIANCE VS CURRENT 140 120 Output Current (µA) Output Current (µA) SRC COMPLIANCE VS CURRENT 140 120 100 80 60 40 20 0 100 80 60 40 20 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 SNK compliance Voltage (V) 0.1 0.2 0.3 0.4 VDD = 3.0V 0.5 0.6 0.7 0.8 Source Compliance Voltage (VDD-SRC) VDD = 3.0V SRC CURRENT VS LIGHT (LUX) 300 Output Current (µA) SRC Current (µA) TYPICAL LOW AMBIENT RESPONSE 1.200 cool w hite Incandescent 1.000 0.800 0.600 0.400 200 100 CHARTS CHARTS 0.200 0.000 0 0 100 200 300 Light Input (LUX) 0 0.2 0.4 0.6 0.8 1 Am bient Light (lux) 8 5 °C 7 5 °C 5 5 °C