microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 1 copyright ? 2007 rev. 1.5b, 2008-01-25 www. microsemi . com lx1970 v isible li g ht sensor p roduction d ata s heet integrated products description 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 10k to 50k 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 key features ? 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 product highlight i snk i src ambient light v out v dd gnd 0.3v typ 0.3v typ 50k 4.7uf lx1970 v dd 50k 4.7uf snk src package order info du plastic msop 8-pin t a ( 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) l l x x 1 1 9 9 7 7 0 0
microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 2 copyright ? 2007 rev. 1.5b, 2008-01-25 www. microsemi . com lx1970 v isible li g ht sensor p roduction d ata s heet integrated products absolute maximum ratings v dd ................................................................................................................. -0.3 to 6 v dc snk/src (output complianc e voltage)........................................... -0.3 to v dd + 0.3v dc snk/src (maximum output cu rrent)................................................... intern ally limited operating temperature range ........................................................................ - 40 to +85c storage temperature ra nge.......................................................................... -40 to +100c solder reflow peak temperature (40 se conds maximum exposur e) ............260c (+0, -5) notes: exceeding these ratings could cause damage to th e device. all voltages are with respect to ground. currents are positive into, ne gative out of specified terminal. thermal data du plastic msop 8-pin thermal resistance - junction to a mbient , ja 206 c/w thermal resistance - junction to c ase , jc 39 c/w package pin out vss nc nc snk vdd nc nc src 1 2 3 5 4 6 7 8 du p ackage (top view) 1 2 3 4 5 6 7 8 1970 xxxx du p ackage (bottom view) xxxx = denotes date code / lot information rohs / pb-free nipdau pin finish msl 2 / 260c / 1 year functional pin description n ame d escription v dd input supply voltage v ss ground reference for power and signal output snk output current sink src output current source simplified block diagram package photo v dd v ss snk src p p a a c c k k a a g g e e d d a a t t a a
microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 3 copyright ? 2007 rev. 1.5b, 2008-01-25 www. microsemi . com lx1970 v isible li g ht sensor p roduction d ata s heet integrated products recommended operating conditions lx1970 parameter min typ max units supply voltage (v dd ) 21 5.5 v snk compliance voltage range v ss +0.5 v dd v src compliance voltage range v ss v dd - 0.5 v snk/src output resistor range 10 1000 k ? note 1: src output will work down to v dd =1.8v electrical characteristics unless otherwise specified, the following specifications apply over the operating ambient temperature -40 c t a 85 c, v dd = 2v to 5.5v, r load = 50kohms, direct light input2 of 14.6w/cm 2 except where otherwise noted. performance between -40c and 0c and between 70c and 85c are assured by design and characterization. lx1970 parameter symbol test conditions min typ max units supply voltage range v dd 2 5.5 v dc input supply current i dd v dd = 3.0v, i src = 38a, i snk = open 60 85 110 a i src v dd = 3.0v 30 38 46 a output current 3 i snk v dd = 3.0v -30 -38 -46 a output snk/src current matching i match v dd = 3.0v 0.5 2 % snk minimum compliance voltage snk vmin v dd = 3.0v, @ 95% of nominal output current v ss +0.3 v ss +0.5 v src maximum compliance voltage src vmax v dd = 3.0v, @ 95% of nominal output current v dd ? 0.3 v dd ? 0.5 v snk/src output dark current i dark v dd = 5.5v, no light 10 300 na wavelength of peak sensitivity ps 520 nm half reception angle ? 60 deg supply voltage coefficient of output current psrr v dd = 2v to 5.5v 2.2 5 %/v sensitivity @ 540nm (peak) irradiance cu rrent responsivity 2.6 a/(w/cm 2 ) sensitivity change @ 910nm 4 current responsivity change with additional direct light input of 14.6w/cm 2 at 910nm -5 0 5 % of peak radiant sensitive area photodiode area 0.369 mm 2 note 2: the input irradiance is supplied from a white li ght-emitting diode (led) optical source adjusted to impose 14.6w/cm 2 at 555nm on the sensor?s surface. note 3: see figure 1 note 4: see figure 2 e e l l e e c c t t r r i i c c a a l l s s
microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 4 copyright ? 2007 rev. 1.5b, 2008-01-25 www. microsemi . com lx1970 v isible li g ht sensor p roduction d ata s heet integrated products measurement circuit configurations a a vdd vs isnk isrc white led current source lx1970 a vdd src ir led 910nm lx1970 white led current sources % figure 1 ? light current measurement circuit figure 2 ? ir sensitivity measurement circuit application notes l ight units in converting from w/cm 2 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. w/cm 2 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 us ed. 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. at 555nm, the conversion factor is 683 lux = 1w/m 2 = 100 w/cm 2 . therefore 14.6 w/cm2 = 100 lux at 555nm. the next step in the conv ersion process is to convert illuminance to luminance. the units for illuminance are lux or lumens/m 2 . the units for luminance are nits or lumens/m 2 /steradian. assuming the illuminance falls on a lambertian surface which has pe rfect 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? li ght 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. a a p p p p l l i i c c a a t t i i o o n n s s
microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 5 copyright ? 2007 rev. 1.5b, 2008-01-25 www. microsemi . com lx1970 v isible li g ht sensor p roduction d ata s heet integrated products application information the lx1970 is a light sensor with a spectral response that resembles the human visual system. it is packaged in clear msop package. microsem i 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: a l i out 76 . 0 = 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 prov ide 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 ca lculated 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 v in = 5v and a 10k resistor src to ground, above about 300ua the output becomes non-linear as it begins to saturate. lx1970 calculated src full range response 0 100 200 300 400 500 600 700 800 900 1000 0 200 400 600 800 1000 1200 light (lux) src current (a) lx1970 src actual src with 10k resistor 0 50 100 150 200 250 300 350 400 450 0 200 400 600 800 1000 1200 light (lux) src current (a) a a p p p p l l i i c c a a t t i i o o n n s s
microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 6 copyright ? 2007 rev. 1.5b, 2008-01-25 www. microsemi . com lx1970 v isible li g ht sensor p roduction d ata s heet integrated products application examples the following examples pres ent 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 we ll 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 si nk and source current of the lx1970 for the target environment and its ambient light conditions. the mechanical m ounting 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. r1 r2 c1 10f 3v to inverter brightness input or led driver controller. n/c 3.3v or 5v vss vdd src snk 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. r2 11 1 0.25v 3.0v r2 r1 = ? = ? ? ? ? ? ? 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 50a . thus r2 can be calculated first order as follows: 275k ? r2 11 r1 25k ? 50a 1.25v r2 = = = = ? ? ? ? ? ? the output node will actually reach 1.25v when the source current from the lx1970 is only about 44a since about 6a 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. r1 40k r2 25k 10f to inverter brightness input or led driver controller input. n/c 3.3v or 5v vss vdd src snk 3.3v pw m 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. 30k 30k 10f to inverter brightness input or led driver controller. n/c vss vdd src snk pwm cmos gate 60k 3.3v diable control 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 applica tion 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. a a p p p p l l i i c c a a t t i i o o n n s s
microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 7 copyright ? 2007 rev. 1.5b, 2008-01-25 www. microsemi . com lx1970 v isible li g ht sensor p roduction d ata s heet integrated products response vs wavelength i snk step response 0 2 4 6 8 10 12 14 16 00.51 time (seconds) amplitude (w/cm 2 ) load = 10k ? and 1f photo step = direct light input of 14.6w/cm 2 small signal frequency response dark current vs temp -45 -40 -35 -30 -25 -20 -15 -10 -5 0 10 100 1000 10000 100000 frequency (hz) amplitude (db) 0.73w/cm2 2.63w/cm2 13.14w/cm2 v dd = 3.0v, snk , three light levels, no filtering 0.01 0.1 1 10 100 1000 25 40 55 70 85 temperature (oc) dark current (na) vdd=5.5v vdd=1.8v snk output psrr gain vs temp -120.00 -100.00 -80.00 -60.00 -40.00 -20.00 0.00 20.00 1 10 100 1000 10000 100000 frequency (hz) amplitude (db) 2.63w/cm2 13.14w/cm2 v dd = 3.0v load = 10k ? and 1f to ground 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 -50 0 50 100 temperature (oc) gain/gain(25oc) y = 1.35e-03x + 9.64e-01 v dd = 3.0v direct light input of 13.14w/cm 2 c c h h a a r r t t s s
microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 8 copyright ? 2007 rev. 1.5b, 2008-01-25 www. microsemi . com lx1970 v isible li g ht sensor p roduction d ata s heet integrated products vertical direction response horizontal dire ction response 1 1 snk compliance vs current src compliance vs current 0 20 40 60 80 100 120 140 0.1 0.2 0.3 0.4 0.5 0.6 0.7 snk compliance voltage (v) output current (a) v dd = 3.0v 0 20 40 60 80 100 120 140 0.10.20.30.40.50.60.70.8 source compliance voltage (vdd-src) output current (a) v dd = 3.0v src current vs light (lux) typical low ambient response 0 100 200 300 0 100 200 300 light input (lux) src current (a) cool w hite incandescent v dd = 5.0v; src = 10k & 4.7f to gnd 0.000 0.200 0.400 0.600 0.800 1.000 1.200 0 0.2 0.4 0.6 0.8 1 ambient light (lux) output current (a) 85c 75c 55c <25c 5v input c c h h a a r r t t s s
microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 9 copyright ? 2007 rev. 1.5b, 2008-01-25 www. microsemi . com lx1970 v isible li g ht sensor p roduction d ata s heet integrated products package dimensions du 8-pin miniature shrink outline package (msop) a1 l e l1 e1 b e s a d c top view side views m illimeters i nches dim min max min max a ? 1.10 ? 0.043 a1 0.05 0.15 0.002 0.006 b 0.26 0.41 0.010 0.016 c 0.13 0.23 0.005 0.009 d 2.90 3.10 0.114 0.122 e 0.65 bsc 0.025 bsc e 4.75 5.05 0.187 0.198 e1 2.90 3.10 0.114 0.122 l 0.41 0.71 0.016 0.028 l1 0.95 bsc 0.037 bsc s 0.525 bsc 0.021 bsc 3 3 active area required minimum light footprint bonding / wafer area examination of active area active area d c c l c l a b p1 m illimeters i nches dim a 0.225 0.0088 b 0.145 0.0057 c 0.600 0.0236 d 0.612 0.0241 p1 2.5 0.98 note: c l 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. m m e e c c h h a a n n i i c c a a l l s s
microsemi analog mixed signal group 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 10 copyright ? 2007 rev. 1.5b, 2008-01-25 www. microsemi . com lx1970 v isible li g ht sensor p roduction d ata s heet integrated products 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. n n o o t t e e s s
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