lx1995 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 miniature led driver copyright ? 2000 rev. 1.1, 2005-07-07 tm ? description the microsemi lx1995-x is a miniature led driver with integrated drivers. it is designed to drive white or color leds in portable display applications. the lx1995-x is an adjustable step-up boost converter. the lx1995-x can switch up to 2mhz allowing designers to use a low cost, small inductor and filter capacitor. the driver supports a wide input voltage range (1.6v to 5.5v) with efficiency greater than 85% and can start up at 1.6v input. the lx1995-x is a low cost, high efficiency led driver. the design is based on a pseudo-hysteretic pulse frequency modulation topology. in portable battery applications the lx1995-x offers high system efficiency with low quiescent current: in operation i q is < 70a and in standby i q is < 1a. the lx1995-x output current is programmable using an external current sense resistor in series with leds. this configuration provides a feedback to the fb pin which maintains constant output current independent of input voltage and led forward voltage (vf). led dimming is accomplished using a pwm signal or varying dc voltage methods. the lx1995-x is available in the 5- pin tsot and sot-23 package. the lx1995-1 can drive up to 6 leds (switching current is 325ma). the lx1995-2 can drive up to 10 leds (switching current is 500ma). important: for the most current data, consult microsemi ?s website: http://www.microsemi.com key features ? < 1a shutdown current ? > 85% maximum efficiency ? efficient at low current levels ? < 70a quiescent supply current in operating mode ? v in range 1.6v to 5.5v ? logic controlled shutdown ? dimming options: pwm or varying dc voltage ? tiny 5-pin tsot package ? smallest external components applications ? pagers ? wireless phones ? pdas ? led driver ? digital camera displays ? gps receivers product highlight lx1995 on off v bat = 2.0v to 5.0v in shdn gnd fb sw package order info sg plastic tsot 5-pin se plastic sot-23 5-pin t a ( c) switch current rohs compliant / pb-free rohs compliant / pb-free transition dc: 0503 -40 to 85 325ma lx1995-1csg lx1995-1cse -40 to 85 500ma lx1995-2csg lx1995-2cse note: available in tape & reel. append the letters ?tr? to the part number. (i.e. lx1995-1csg-tr) l l x x 1 1 9 9 9 9 5 5
lx1995 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 miniature led driver copyright ? 2000 rev. 1.1, 2005-07-07 tm ? absolute maximum ratings supply input voltage ........................................................................-0.3v to 7.0v feedback peak pulse input voltage (v fb ) ..............................-0.3v to v in + 0.3v shutdown input voltage (v shdn ) ...........................................-0.3v to v in + 0.3v switch voltage (v sw ) ........................................................................-0.3v to 30v switch current (i sw ) ...................................................................................500ma operating temperature range .........................................................-40 c to 85 c maximum operating junc tion temperat ure ................................................ 125 c storage temperature range...........................................................-65 c to 150 c peak package solder reflow temp. (40 second max. 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 sg plastic tsot 5-pin thermal resistance - junction to a mbient , ja 207 c/w se plastic sot-23 5-pin thermal resistance - junction to a mbient , ja 191 c/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 1 2 34 5 sw gnd fb in shdn sg p ackage (top view) in sw fb gnd 1 2 34 5 shdn se p ackage (top view) rohs / pb-free 100% matte tin lead finish functional pin description name description sw inductor switching connection ? internally connected to the drain of a 28v n-channel mosfet. sw is high impedance in shutdown. gnd common terminal for ground reference. fb feedback input ? connect to a current sense resistor between the load and gnd to set the maximum output current. fb pin is regulated to 320mv. shdn active-low shutdown input ? a logic low shuts down the device and reduces the supply current to <1 a. connect shdn to v cc for normal operation. in unregulated ic supply voltage i nput ? input range from +2.0v to +5.5v. bypass with a 1 f or greater capacitor for low voltage operation. p p a a c c k k a a g g e e d d a a t t a a
lx1995 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 miniature led driver copyright ? 2000 rev. 1.1, 2005-07-07 tm ? electrical characteristics unless otherwise specified, the following specif ications apply over the operating ambient 1 temperature 0 c t a 70 c except where otherwise noted and the following test conditions: v in = 3v, v shdn = v in . unless where indicated, these parameters apply to both the lx1995-1 and lx1995-2 part versions. lx1995-x parameter symbol test conditions min typ max units operating voltage v in 1.6 5.5 v minimum start-up voltage v su t a = +25 c 1.6 v start-up voltage temperature coefficient k vst guaranteed; not tested -2 mv/ c not switching 70 100 quiescent current i q v shdn < 0.4v 0.2 0.5 a fb threshold voltage v fb(th) 288 320 352 mv fb input bias current i fb not switching, v fb = 400mv -10 10 na shutdown input bias current i shdn v shdn = 0v -100 100 na shutdown low input voltage 0.6 shutdown high input voltage v shdn 1.4 v switch peak current i peak l= 47 h; lx1995-1 250 325 400 ma switch peak current i peak l= 47 h; lx1995-2 400 500 600 ma minimum switch off-time t off t a = +25 c; v fb < v fb(th) 300 ns switch pin leakage current i leak v sw = 28v 0.23 a note: 1. low duty cycle pulse testing tec hniques are used which maintains junction and case temperatures equal to the ambient temperatur e. 2. functionality over the -40 c to +85 c operating temperature range is assured by design, characterizati on, and correlation. simplified block diagram control logic driver v fb sw gnd in shdn reference bias figure 1 ? simplified block diagram e e l l e e c c t t r r i i c c a a l l s s
lx1995 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 miniature led driver copyright ? 2000 rev. 1.1, 2005-07-07 tm ? application circuits lx1995 v bat = 2.0v to 5.0v in shdn gnd fb sw l 1 10 h 1206 case size c 1 0.1 f r 1 15 ? 100hz to 1khz d 1 figure 2 ? typical bust mode dimming led driver application lx1995 v bat = 2.0v to 5.5v in shdn gnd fb sw l 1 10 h 1206 case size c 1 0.1 f r 1 17.4 ? d 1 on off r 3 100k ? r 2 17.4k ? v dc = 0v to 2.0v i led = 0ma to 20ma figure 3 ? analog voltage dimming led driver application the component values shown are only examples for a worki ng system. actual values will vary greatly depending on desired parameters, efficiency, and layout constraints. a a p p p p l l i i c c a a t t i i o o n n s s
lx1995 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 miniature led driver copyright ? 2000 rev. 1.1, 2005-07-07 tm ? application circuits lx1995 v bat = 2.0v to 5.0v in shdn gnd fb sw l 1 10 h 1206 case size c 1 0.1 f r 1 15 ? d 1 on off r 2 11.2k ? r 3 90.9k ? c 2 0.1 f r 4 9.09k ? >10khz v pwm = 3.3v dc = 10% to 90% i led = 0ma to 20ma figure 4 ? pwm to analog voltage dimming led driver application c 1 .1 f l 1 10 h 1206 case size lx1995 gnd fb sw shdn in v bat = 2.0v to 5.0v on off r 2r 2r - r a lsb msb v cc v cc r a 320mv r a = (0.64 x r) / v cc lsb msb i led 11 10 0 1 0.75 x i max 00i max r cs rcs = (0.32 x r) / {[r - (0.375 x r a )] x i max } 0.50 x i max 0.25 x i max figure 5 ? binary dimming led driver application the component values shown are only examples for a working syst em. actual values will vary greatly depending on desired parame ters, efficiency, and layout constraints. a a p p p p l l i i c c a a t t i i o o n n s s
lx1995 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 miniature led driver copyright ? 2000 rev. 1.1, 2005-07-07 tm ? theory of operation o perating t heory the lx1995-x is a pfm boost converter optimized for driving a series of white or co lor leds. it operates in a pseudo-hysteretic mode with a fixed, 300ns, switch ?off time?. when the lx1995-x enables, the led current decreases causing the fb voltage to decrease to a value less than 320mv. the feedback comparator (see simplified block diagram) activates the control logic. the control logic turns on the drv output circuit that connects to the internal n-channel mosfet gate. the switch output (sw) is switched ?on? and remains ?on? until the inductor current ramps up to the peak current level (typically 325ma for lx1995-1). the led load is powered from energy stored in the output capacitor during the indu ctor charging cycle. once the peak inductor current value is achieved, the output is turned off and the energy stored in the inductor delivers to the load. this causes the volt age to rise across the current setting resistor (r 1 ) at the input to the fe edback circuit. the lx1995-x continues to switch until the voltage at the fb pin exceeds 320mv. the value of r 1 is calculated by dividing 320mv by the maximum series led current. a minimum value of 3.3 ? is recommended for r set . the voltage at the fb pin is the product of the led current (i led ) and r 1 . ) max ( led 1 i mv 320 r = eq. 1 d imming m ethods lx1995-x supports two dimming methods: pwm or dc voltage. pwm mode: connect system pwm logic signal to the shdn pin (see figure 1). this turns the lx1995-x on and off which pulses the led current between zero and the setting determined by r 1 . dc voltage mode: the designer can apply an adjustable dc voltage supply to the fb pin. as the dc voltage increases, the led current decreases. the equation (see figure 3) is: ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + ? = 3 2 adj 3 3 2 1 led r r v r r r mv 320 r 1 i eq. 2 i nductor s election and o utput c urrent l imit p rogramming microsemi recommends the use inductors (for the lx1995-1) in the range of 10h to 47h due to saturation of peak inductor current. by increasing the average inductor current, the lx1995-x will extend the power range. smaller inductor values will reduce output voltage ripple and are smaller in size. o utput r ipple and c apacitor s election output voltage ripple is depended on the selection of the inductor value (l), output capacitor value (c out ), peak switch current (i peak ), load current (i out ), input voltage (v in ) and the output voltage (v out ). the peak-to-peak voltage ripple is a function of the output droop (as the inductor curren t charges to i peak ), the feedback transition error (i.e., typically 10mv), and the output overshoot (energy stored in the inductor). when the switch is first turn on, the total ripple voltage is: 10mv v v v overshoot droop ripple + ? + ? = eq. 3 the initial droop can be estimated with the assumption of 0.5v of voltage drop across the inductor and fet rds on . () 5 . 0 v i i c l v in led pk out droop ? ? ? ? ? ? ? ? ? ? = ? eq. 4 the output overshoot calculated with 0.5v as voltage drop across the diode. () 5 . 0 v v i i c l 2 1 v in out 2 led pk out overshoot + ? ? ? ? ? ? ? ? ? ? ? ? = ? eq. 5 once the output voltage ripple is determined for the selected components, the output capacitor can then be adjusted to meet the target ripple voltage requirements. the lx1995-x is targeted for led driver applications; output voltage ripple is not a critical application requirement. a a p p p p l l i i c c a a t t i i o o n n s s
lx1995 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 miniature led driver copyright ? 2000 rev. 1.1, 2005-07-07 tm ? lx1995-1 efficiency lx1995-2 efficiency efficiency led current 50 60 70 80 90 100 2468101214161820 47h inductor, 4 white leds 5.0v in 3.5v in efficiency led current 50 60 70 80 90 100 2468101214161820 47h inductor, 4 white leds 5.0v in 3.5v in c c h h a a r r t t s s
lx1995 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 miniature led driver copyright ? 2000 rev. 1.1, 2005-07-07 tm ? package dimensions sg 5-pin thin shrink small outline package (tsot) e1 e e b e1 d a2 a a1 c l2 l 1 2 3 45 m illimeters i nches dim min max min max a - 1.00 - 0.039 a1 0.01 0.10 0.0004 0.004 a2 0.84 0.90 0.033 0.035 b 0.30 0.45 0.012 0.018 c 0.12 0.20 0.005 0.008 d 2.90 bsc 0.114 bsc e 2.80 bsc 0.110 bsc e1 1.60 bsc 0.063 bsc e 0.95 bsc 0.037 bsc l 0.30 0.40 0.012 0.016 l2 0.25 bsc 0.010 bsc se 5-pin small outline package (sot-23) h g f e a1 j i c k a b d m illimeters i nches dim min max min max a 0.90 1.30 0.035 0.051 a1 0.90 1.45 0.035 0.057 b 0.25 0.50 0.010 0.020 c 0.09 0.20 0.004 0.008 d 2.80 3.10 0.110 0.122 e 1.50 1.75 0.059 0.069 f 0.95 bsc 0.038 bsc g 1.90 bsc 0.075 bsc h 2.60 3.00 0.102 0.118 i 0.35 0.55 0.014 0.022 j 0.00 0.15 0.000 0.006 k 10 max 10 max note: dimensions do not include mold flash or pr otrusions; these shall not exceed 0.155mm(.0 06?) on any side. lead dimension shall not include solder coverage. m m e e c c h h a a n n i i c c a a l l s s
lx1995 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 miniature led driver copyright ? 2000 rev. 1.1, 2005-07-07 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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