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microsemi integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 1 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink tm ? description the lx1990 is a dual output current sink optimized for driving light emitting diodes. this low cost bipolar ic enables precise current regulation in led display lighting applications, yet requires far fewer parts than discrete solutions. the lx1990 is supplied in a micro-miniature 6 lead mlp package featuring a 3 x 3 mm footprint, a profile of less than 1mm, and much improved thermal performance. its two output sink currents are accurately matched and require only one resistor to program. program current is only 1% of the output currents, and quiescent current is low, providing a very high efficiency driver for battery-powered displays. the lx1990 is based on a current- mirror architecture that transfers a reference current produced at the i set pin to each of two open-collector current sinking outputs. the output stages multiply this reference current by 100 to sink independently regulated currents up to 30 ma. light output from led?s is proportional to average current through them; they can easily produce a brightness range of 500:1. however, color of emitted light is shifted by current amplitude. color shift at low ligh t levels can be reduced by driving the led?s with a constant peak current while dimming with duty cycle control. this is achieved by driving the i set resistor with a pwm signal. a 500:1 b rightness range can be achieved by choosing 270 hz as the pwm frequency (to avoid optical beating with 50/60 hz roo m lights) and pulse width from 3.7 milliseconds to 7.4 microseconds. the lx1990 features a shutdown mode via the enable pin. in this mode the lx1990 consumes less than 1 a and holds the two open collector output stages off. this pin may also be used to pulse width modulate output current. see applications section for dimming details. important: for the most current data, consult microsemi ?s website: http://www.microsemi.com key features ? programmable sink current 0.1 to 30ma x 2 channels ? replaces discrete transistor circuitry with a single package ? 300mv maximum current sink dropout voltage at 20ma ? 2.7 to 5.5v power supply input ? i out compliance voltage from 0.1 to 10v dc ? enable input with <1a sleep current ? amplitude and pwm dimming ? current rise and fall time may be controlled to reduce emi applications ? cell phone display illumination ? pda white led display lighting ? automotive disp lay illumination ? digital still camera ? camcorders ? consumer electronics front panels product highlight 5v lx1990 vdd i outb gnd i outa iset r set ena v load on/off package order info lm plastic mlp 6-pin t a ( c) rohs compliant / pb-free transition dc: 0452 -40 to 85 lx1990ilm note: available in tape & reel. append the letters ?tr? to the part number. (i.e. LX1990ILM-TR) l l x x 1 1 9 9 9 9 0 0
microsemi integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 2 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink tm ? absolute maximum ratings supply voltage (v dd ) ....................................................................................... 6v ena voltage..................................................................................................... 6v i set maximum current.............................................................. internally limited i set maximum voltage .................................................................................. v dd i out maximum compliance voltage ...............................................................12v current source outputs.............................................................................. 100ma operating temperature ra nge .........................................................-40c to 85c maximum junction temperature ................................................................. 125c storage temperature......................................................................-65c to 150c peak package solder reflow temperature (40 seconds 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 lm plastic mlp 6-pin thermal resistance - junction to a mbient , ja 41 c/w junction temperature calculation: t j = t a + (p d x ja ). the ja numbers are guidelines for the ther mal performance of the device/pc-board system. all of the above assume no ambient airflow. package pin out vdd ena gnd i outb i outa iset 1 2 3 4 5 6 lm p ackage (top view) 1990 xxxx lmi lm p ackage m arkings xxxx ? denotes date code / lot identification rohs / pb-free 100% matte tin lead finish functional pin description n ame d escription v dd input supply gnd common ground reference ena chip enable input. if logic high, current source outputs ar e enabled. if logic low, internal power is disconnected from the vdd pin, disabling all f unctions. logic threshold is 1.2 v. i outa & i outb output current source. two separate constant current outputs. outputs may be loaded in any combination without affecting regulation of the loaded output. if only one output is needed i outa & i outb must be shorted together. in this case the value of iset resistor mu st be doubled. compliance voltage range is 0.1v to 10v. i set output current programming pin. p p a a c c k k a a g g e e d d a a t t a a
microsemi integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 3 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink tm ? recommended operating conditions lx1990 parameter min typ max units supply voltage (v dd ) 2.7 5.5 v ena (enable) input voltage 0 v dd v i set voltage 0 1.25 v i set current 0 300 a i outa / i outb compliance voltage range 0.1 10 v i outa / i outb output current range 0.1 30 ma electrical characteristics unless otherwise specified, the following specifications apply over the operating ambient temperature -40 c t a 85 c and the following test conditions: v dd = 2.7 to 5.5 v dc , i set = 200a , v out 5.5v, vload 10v. typical values are at t a = 25c lx1990 parameter symbol test conditions min typ max units power characteristics quiescent current i _qui vdd = 2.7v; iset = 0ua 1.4 2 ma quiescent current i _qui vdd = 5.5v; iset = 300ua 3.0 4 ma sleep current 1 i _sleep vdd = 5.5v, ena 0.4v 0.08 1 a enable input enable logic threshold v th_en 0.8 1.55 2.4 v enable input current i in_en ena = v dd = 5.5v 4 10 a i set to out pulse response t d(on) 1.2 2 s i set to out pulse response t d(off) 1.4 2 s iset input i set current range i iset r set terminated to gnd 0 300 a i set voltage v iset i set = 200ua 1.225 1.25 1.275 v dc output characteristics output current amplitude i out 0.5 < v out < 5.5v, i set = 200a 18.5 20 21.5 ma dc outa to outb current matching i out_match i out = 20ma ; (i outa ? i outb ) / i outa * 100 0.4 5 % iset to iout current ratio i out_ratio i out /i set ; i set = 200a ; v dd = 5.5v 102 iset to iout current ratio i out_ratio i out /i set ; i set = 200a ; v dd = 2.7v 99 output current i set = 0a i out_zero 0.5 < v out < v load , i set = 0a 10 100 a dc dropout voltage 2 v dropout i out = 20ma 150 300 mv dropout voltage 2 v dropout i out = 30ma 200 400 mv maximum output current, i set shorted to gnd. each output i sc v iset = zero volts; vdd=5v 100 ma dc output off state current i outoff ena 0.4v 20 a dc 1 at enable voltages greater than 0.4v but less than 0.8v the outputs will remain off but the sleep current may be greater than 1a. 2 dropout is defined as the outa/b to gnd voltage at which the output current sink drops 10% from the nominal value. e e l l e e c c t t r r i i c c a a l l s s
microsemi integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 4 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink tm ? simplified block diagram vdd enable + - iset 1:1 current mirror 100x 100x gnd i outa i outb 1.25v ref bias figure 1 ? simplified block diagram b b l l o o c c k k d d i i a a g g r r a a m m
microsemi integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 5 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink tm ? applications f unctional d escription the lx1990 is designed to drive led?s used in display illumination and signaling applications such as cellular telephones and pda?s. with a 5v supply, the two independently regulated constant current outputs can drive 2 white led?s (v f < 4.5v) in parallel, or 4 green or amber led?s (v f < 2.25v each) arranged as 2 parallel x 2 in series. with dropout voltage of only 300 mv at 20 ma, the lx1990 provides regulated current for 2 green / amber led?s in a cell phone all the way down to the minimum nicd cutoff of 2.7 volts for three cells. the lx1990 features resistor settable output current. connecting a resistor between i set and a voltage of zero to 1.25 volts generates a current that is mirrored into each of the output with a gain of about 100. output current can be varied in an analog fashion by varying i set resistance or termination voltage (see application schematics). duty cycle dimming with a fixed current amplitude is accomplished by switching the i set current on and off with an open collector or open drain pulse width modulated logic signal. sw itching frequency can exceed 20 khz, making it practical to use a pwm output channel from popular micro controllers. the upper limit on frequency is minimum switching response from i set to output. as frequency increases, these fixed delays will cause an error in expected output current duty cycle. all inputs and outputs are esd and short circuit protected making the lx1990 an exceptionally robust component. however it is not recommended to indefinitely short the i set input to ground while shorting the outputs to 10v as the power dissipation under these conditions is the greatest. a pplication n otes each output has an independent current sink, however both must be held above about 0.5 volts to maintain specified current regulation accuracy. if only one output is needed, the two outputs should be connected together and the programming resistor value doubled so each output supplies ? the desired current. in this case, more than 60 ma total current can be delivered from the combined output. package power dissipation can be calculated from the following equation: ()( ) ed load l out d v v i n p ? ? ? = n = number of outputs used i out = current from each output v load = output supply voltage v led = minimum led forward voltage p d = power dissipated in mw when the ena input is at zero volts, less than 20a current flows into or out of the outputs. if the disable function is used , ena must be driven below 0.4 volts to insure minimum current from v dd . the i set pin may be driven with a digital open collector or open drain logic pwm signal to dim the led?s. recommended pwm frequency for dimming is between 100 hz and 20 khz. below 100 hz flicker may be observed. above 20 khz duty cycle accuracy is reduced due to switching delays from i set to outputs. totem pole output drive may also be used as long as the maximum driver voltage never exceeds the v dd supply. since the totem pole drive will exceed the 1.25v i set voltage it can introduce delays that may limit the useful frequency and maximum dim range. if pwm dimming is used, use separate power and ground lines directly from the power source point to prevent noise generated from the led current transients from entering video or audio subsystems on the same supply rails. additional power supply filtering may be needed in pwm dimming applications. care should be exercised in the pcb layout to prevent coupling from the outputs to the i set pin, as this may cause the part to oscillate. current out of the i set pin may be varied for current amplitude dimming. there are two ways to do this: if a mechanical input is needed, a rheostat in series with a resistor connected from gnd to i set can be used. the second method is to connect a fixed resistor from i set to the output of a voltage dac or other low impedance voltage source. varying the voltage between zero and 1.25 volts will cause a corresponding output current change from i out max to zero: set out i ratio current i = the ena pin may be used to duty cycle dim the output in applications where only one control line is available for dimming and shutdown. a narrow current spike that may be as high as 100 ma is produced when the ena signal has very fast rise times. this is not harmful to the led, but will cause dimming linearity errors when operating at very low duty cycles. 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 integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 6 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink tm ? typical characteristics vdd = 5v, ena = 5v, i set = 200a, t a = 25c. unless otherwise noted. i out vs. temperature @ i set = 200a 19 . 6 19 . 8 20 20.2 20.4 20.6 20.8 -45-205305580105130 temp (c) i out current (ma) iout a @ 2.7v ioutb @ 2.7v iouta @ 5v ioutb @ 5v output off leakage current vs.v out ena=0.4v 0 2 4 6 8 10 12 14 02 4681012 v out (v) i out leakage (a) 2.7v 5v 5.5v i out vs i set 0 5 10 15 20 25 30 35 40 45 0 50 100 150 200 250 300 350 400 i set (a) i out (ma) 2.7v 5.5v 5v v dropout vs. current 0 5 10 15 20 25 30 35 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 dropout (v) i out (ma) 5ma 10ma 15ma 20ma 25ma 30ma output current vs. vdd 19 . 9 20 20.1 20.2 20.3 20.4 20.5 20.6 20.7 2.73.74.75.7 vdd (v) output current (ma) bout aout enable to output response ena 2v / div iout 1 0ma / div 10 s / div c c h h a a r r t t s s
microsemi integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 7 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink tm ? applications 4k 3.3v v load vdd ena iset gnd i outa i outb on/off open collector or open drain drive .1f 100k +5v vdd ena iset gnd i outa i outb on/off 4k load up to 10 volts 4k wht grn grn +5v vdd ena iset gnd i outa i outb d0 d1 d2 d3 out 1.25v on/off .1f figure 2 ? auto dashboard or instrument front panel led array figure 3 ? color lcd display & keypad illumination figure 4 ? variable current driver 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 integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 8 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink tm ? dimming methods vdd ena iset gnd i outa i outb pwm r set vdd ena iset gnd i outa i outb on / off r min r step vdd ena iset gnd i outa i outb 3v r min r max figure 5 ? pwm on enabled (lowest iq) figure 6 ? precision 2 steps figure 7 ? manual control vdd ena iset gnd i outa i outb on / off r set pwm vdd ena iset gnd i outa i outb 1k c slope 5k 10k 100k pwm 2n2222a 8.2nf vdd ena iset gnd i outa i outb 6.3k 2n2222 10k 100k pwm on / off 1v / div 10 s / div 10ma / div 1v / div 20s / div 10a / div 1v / div 20s / div 10ma / div figure 8 ? pwm dimming totem pole output figure 9 ? pwm ? low emi wide range figure 10 ? pwm ? wide range 500:1 + 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 integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 9 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink tm ? application vdd ena iset gnd i outa i outb r set 100k 10k pw m 20k bc846b x2 20k .47f 3.3v 10 w hite leds each output 48v on/off 2.2k lx432sc optional circuit for higher efficiency figure 11 ? using the lx1990 with high voltage supplies 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 integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 10 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink tm ? package dimensions lm 6-pin plastic mlp-micro exposed pad g a b f h e d c internally connected together, but isolated from all other terminals k j i note: 1. dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006?) on any side. lead dimension shall not include solder coverage. m illimeters i nches dim min max min max a 2.90 3.10 0.114 0.122 b 2.90 3.10 0.114 0.122 c 0.65 0.75 0.025 0.029 d 0.15 0.25 0.005 0.009 e 1.841 bsc 0.075 bsc f 0.27 0.43 0.010 0.016 g 0.95 bsc 0.037 bsc h 1.22 bsc 0.048 bsc i 0 0.10 0 0.003 j 0.21 0.37 0.008 0.014 k 0 0.10 0 0.003 m m e e c c h h a a n n i i c c a a l l s s
microsemi integrated products 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 11 copyright ? 2001 rev. 1.0d, 2005-03-14 www. microsemi . com lx1990 dual pro g rammable led current sink 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. pr oduct 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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