LX1974 p roduction d ata s heet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 1 www. microsemi . com ambient light detector copyright ? 2005 rev. 1.0, 2006-05-09 tm ? description the LX1974 is a low cost silicon light sensor with spectral response that closely emulates the human eye. patented circuitry produces peak spectral response at 520nm, with ir response less than 5%, of the peak response, above 900nm. the photo sensor is a pin diode array with 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 10k to 100k) and power supply values. typically the LX1974 needs only 1.8v 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 (-40 to +85c), providing high accuracy at low light levels. usable ambient light conditions range is from 1 to more than 5000 lux. the LX1974 is optimized for controlling back lighting systems in low cost consumer products such as lcd tv, portable computers, and digital cameras. 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 ? 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 ? portable electronic displays ? lcd tv backlight systems ? digital still cameras (dsc) ? desktop monitors ? notebook computers product highlight LX1974 light package order info bc plastic 1206 2-pin t a ( c) rohs compliant / pb-free -40 to 85 LX1974ibc note: available in tape & reel. append the letters ?tr? to the part number. (i.e. LX1974ibc-tr) l l x x 1 1 9 9 7 7 4 4
LX1974 p roduction d ata s heet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 2 www. microsemi . com ambient light detector copyright ? 2005 rev. 1.0, 2006-05-09 tm ? absolute maximum ratings supply input volta ge ...........................................................................-0.3v to 6v ground current ..........................................................................in ternally limited operating temperat ure range .........................................................-40 c to 85 c maximum operating junc tion temperat ure ................................................ 150 c storage temperat ure range.........................................................-40 c to +100 c rohs / pb-free peak package solder reflow temperature (40 second maximum 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 . thermal data bc plastic 1206 2-pin thermal resistance - junction to a mbient , ja 850c/w junction temperature calculation: t j = t a + (p d x ja ). the ja numbers are guidelines for the thermal performan ce of the device/pc-board system. all of the above assume no ambient airflow. package pin out vdd vss 1 2 bc p ackage (top view) rohs / pb-free gold lead finish functional pin description name description vdd positive terminal vss negative terminal characteristic curves chart 1 & 2 ? step response graphs vdd = 4v, 200 to 20 lux step 30.3k load resistance p p a a c c k k a a g g e e d d a a t t a a
LX1974 p roduction d ata s heet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 3 www. microsemi . com ambient light detector copyright ? 2005 rev. 1.0, 2006-05-09 tm ? characteristic curves chart 3 ? response vs. wavelenght 0.0 0.5 1.0 1.5 2.0 2.5 -40-20 0 20406080 temperature (c) operating voltage 10a 100a 200a chart 4 ? typical operating voltage vs vss current 0 50 100 150 200 250 300 -40-20020406080100 temperature (c) dark current (na) chart 5 ? dark leakages vs. temperature iout @ 1000 lux, vdd=5.0v, 10k load 60 70 80 90 100 110 120 130 140 150 -60 -40 -20 0 20 40 60 80 100 temperature ua chart 6 ? typical temperature response c c h h a a r r t t s s
LX1974 p roduction d ata s heet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 4 www. microsemi . com ambient light detector copyright ? 2005 rev. 1.0, 2006-05-09 tm ? electrical characteristics unless otherwise specified, the following specifications apply over the operating ambient temperature -40 c t a 85 c except where otherwise noted and the following test conditions: see note 1, v dd =5v, r ss = 10k LX1974 parameter symbol test conditions min typ max units ` response peak spectral response pr 520 nm infrared response ) ( i ) ( i pr dd dd e v(550nm) = 292 w/cm 2 , current responsivity change with additional direct light input of 292 w/cm 2 at 910nm, note 3 -5 1 5 % e v = 14.6 w/cm 2 , i ss = 10 a 1.2 1.4 e v = 146 w/cm 2 , i ss = 100 a 1.8 2.1 minimum operational voltage v dd -v ss e v = 292 w/cm 2 , i ss = 200 a 2.2 2.6 v e v = 14.6 w/cm 2 (100 lux), note 2 7.5 10 12.5 e v = 146 w/cm 2 (1k lux), note 2 75 100 125 light current i ss e v = 292 w/cm 2 (2k lux), note 2 150 200 250 a gain linearity 14.6 w/cm 2 e v 146 w/cm 2 @ 25c -15 15 % e v = 0 w/cm 2 , t a = 25 c 0.010 50 dark current i dd(dark) e v = 0 w/cm 2 200 na power supply rejection ratio psrr v ripple = 10mv p-p , f = 10khz -25 db radiant sensitive area 0.04 mm 2 notes: 1. the input irradiance (e v ) is supplied from a white light-e mitting diode (led) optical source adjusted to impose the specified e v at a peak = 550nm. 2. see figure 1. 3. see figure 2. test circuits LX1974 v ss v dd white led 10k figure 1 ? operational voltage measurement circuit LX1974 v ss v dd white led 910nm 10k figure 2 ? ir sensitivity measurement circuit e e l l e e c c t t r r i i c c a a l l s s
LX1974 p roduction d ata s heet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 5 www. microsemi . com ambient light detector copyright ? 2005 rev. 1.0, 2006-05-09 tm ? simplified block diagram current amp vdd vss figure 3 ? simplified block diagram application note l ight units in converting from w/cm 2 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/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 (dar k adapted eye) is used. if the light is composed of only one wavelength, a conversion chart will tell the co nversion 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/m 2 = 100 w/cm 2 . therefore 14.6 w/cm 2 = 100 lux at 555nm. 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 LX1974 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 fluore scent 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 LX1974 the ate (automatic test equipment) light source is configured with white led?s whose current is adjusted to output a calibrated flux density at 550nm. 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. a a p p p p l l i i c c a a t t i i o o n n s s
LX1974 p roduction d ata s heet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 6 www. microsemi . com ambient light detector copyright ? 2005 rev. 1.0, 2006-05-09 tm ? 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 LX1974 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, lx1993, lx1994, and lx1995. in each specific application, it is important to recognize the need to correlate the out put current of the LX1974 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 LX1974 for a given exposure of light. r1 r2 c1 10f 3v to inverter brightness input or led driver controller. 3.3v or 5v vss vdd figure 4 ? fully automatic dimming 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 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 LX1974 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 r each 1.25v when the source current from the LX1974 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 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. r1 40k r2 25k 10f to inverter brightness input or led driver controller input. 3.3v or 5v vss vdd 3.3v pwm figure 5 ? semi-manual controlled dimming 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 LX1974, a diode has been inserted to isolate the sensor when it is disabled. 30k 30k 10f to inverter brightness input or led driver controller. vss vdd pwm cmos gate 60k 3.3v disable control figure 6 ? fully manual controlled dimming 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 microsemi?s website: www.microsemi.com . although this application note is written around the lx1970 visible light sensor the circuits can be easily adapted for use with the LX1974. a a p p p p l l i i c c a a t t i i o o n n s s
LX1974 p roduction d ata s heet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 7 www. microsemi . com ambient light detector copyright ? 2005 rev. 1.0, 2006-05-09 tm ? application circuits vss vdd LX1974 lx1995 in shdn gnd sw fb shdn c1 4.7f r1 100k gnd vin l1 10h d1 ups5817 c2 1f r6 15 r5 5.76k r4 10k c3 10f c4 0.1f r10 49.9k r8 60.4k 3.3v r7 24.9k b a c k l i g h t mmbt2907 figure 7 ? typical application with microsemi?s lx1995 led driver ic vin s/p brt ls gnd drv src ovp fb cmp 22h fdn337 ups5819 1m 41.2k 0.1f 4.99k 1f 15k 22f 178k 100k vdd vss 3.3v 1f 15 v in = 2.0v to 5.5v pwm dimming input LX1974 lx1994 mmbt2907 figure 8 ? typical application with microsemi?s lx1994 led driver ic a a p p p p l l i i c c a a t t i i o o n n s s
LX1974 p roduction d ata s heet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 8 www. microsemi . com ambient light detector copyright ? 2005 rev. 1.0, 2006-05-09 tm ? package dimensions bc 2-pin 1206 standard carrier d p h e side top bottom 1 2 1 a x r pin 1 indicator (top side) / alignment indicator (bottom side) b c l c l 0.03 0.19 - 0.25mm sensor active area: 0.2 x 0.2mm sensor active area c 2 c m illimeters i nches dim min max min max a 0.95 1.25 0.037 0.049 b 0.40 0.70 0.016 0.028 c 0.90 1.10 0.035 0.043 d 3.05 3.35 0.120 0.132 e 1.90 2.10 0.075 0.083 h 0.40 0.60 0.016 0.024 3 nom 3 nom p 1.45 1.75 0.057 0.069 r 0.25 nom 0.010 nom x 0.02 0.05 0.001 0.002 note: dimensions do not include protru sions; these shall not excee 0.155mm (.006?) on any side. 1.50mm 0.06in. 2.0mm 0.08in. 1.50mm 0.06in. 1.50mm 0.06in. super imposed 1206 package recommended soldering pattern for reflow soldering of the bc (1206) package. basic specification is < 5 seconds @ 260c when applying solder. 8.00 5.25 1.75 4.00 2.00 4.00 lead in: 10 min empty loaded: 3000 pcs lead out: 40 min empty 1.30 0.20 note: LX1974 parts are loaded bottom side up m m e e c c h h a a n n i i c c a a l l s s
LX1974 p roduction d ata s heet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 9 www. microsemi . com ambient light detector copyright ? 2005 rev. 1.0, 2006-05-09 tm ? 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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