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lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 1 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? description the lx1745 is a compact high efficiency step-up boost regulator for driving white or color leds in lcd lighting applications while supplying the necessary lcd bias voltages with an additional two integrated boost converters. designed for maximu m efficiency and featuring a psuedo-hysteretic pfm topology (that decreases output voltage ripple), the lx1745 minimizes system cost and condenses layout area making it ideal for pda, smart-phone, and digital camera applications. while the lcd bias generation is implemented using an internal n-channel mosfet for lcd bias generation, the led driver utilizes an external n-channel mosfet in order to maintain maximum efficiency along with flexible power requirements.. the lx1745?s control circuitry is optimized for portable systems with a shutdown current of less than 1a. the input voltage range of 1.6v to 6.0 allows for a wide selection of system battery voltages and start-up is guaranteed at a v in equal to 1.6v with sustained operation as low as 1.1v. the maximum led drive current is easily programmed using one external current sense resistor in series with the leds. in this configuration, led current provides a feedback signal to the fb pin, maintaining constant current regardless of varying led forward voltage (v f ). depending on the mosfet selected, the lx1745 is capable of achieving an led drive in excess of 1.0w. the lx1745 provides simple dynamic adjustment of the led drive current (0% to 100% full range dimming) and the lcd bias output voltages (up to 15% typ) through separate ic interfaces. each interface has an internal rc filter allowing designers to make these adjustments via a direct pwm input signal or an analog reference signal. further, any pwm amplitude is easily accommodated using a single external resistor. the lx1745 is available in the low- profile 20-pin tssop. important: for the most current data, consult microsemi ?s website: http://www.microsemi.com key features ? > 90% maximum efficiency ? low quiescent supply current ? externally programmable peak inductor current limit for maximum efficiency ? logic controlled shutdown ? < 1a shutdown current ? dynamic output led current and two lcd bias voltage adjustments via analog reference or direct pwm input ? 20-pin tssop package applications ? pagers ? smart phones ? pdas ? handheld computers ? general lcd bias applications ? led driver product highlight c 1 4.7 f l 1 47 h 1206 case size lx1745 lfb cs drv in src r set 15 v bat = 1.6v to 6.0v i led = 20ma to 0ma ovp sw1 v lcd1 = v in to 25v fb1 - v lcd brt lshdn on off sw2 fb2 v lcd2 = v in to 25v ref adj1 shdn1 on off gnd adj2 shdn2 on off lx1745 evaluation board package order info pw plastic tssop 20-pin t a ( c) rohs compliant / pb-free transition dc: 0442 -40 to 85 lx1745cpw note: available in tape & reel. append the letters ?tr? to the part number. (i.e. LX1745CPW-TR) l l x x 1 1 7 7 4 4 5 5
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 2 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? absolute maximum ratings supply input volta ge ...........................................................................-0.3v to 7v feedback input voltage (v fbx ) ...............................................-0.3v to v in + 0.3v shutdown input voltage (v shdn x ) ..........................................-0.3v to v in + 0.3v pwm input amplitude (adj x, brt).....................................-0.3v to v in + 0.3v analog adjust input voltage (v adjx , v brt )............................-0.3v to v in + 0.3v src input curr ent ................................................................................ 500ma rms operating temperat ure range .........................................................-40 c to 85 c maximum operating junc tion temperat ure ................................................ 150 c storage temperat ure range...........................................................-65 c to 150 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 . x denotes respective pin designator 1, 2, or 3 thermal data pw plastic tssop 20-pin thermal resistance - junction to a mbient , ja 90 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 gnd drv gnd fb1 ref brt sw1 adj1 in src 1 2 8 7 14 17 20 19 3 5 9 12 18 16 6 4 ovp cs 15 13 sw2 10 11 shdn1 lshdn shdn2 lfb adj2 fb2 gnd pw p ackage (top view) rohs / pb-free 100% matte tin lead finish p p a a c c k k a a g g e e d d a a t t a a
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 3 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? functional pin description name description in unregulated ic supply voltage i nput ? input range from +1.6v to 6.0v. bypass with a 1 f or greater capacitor for operation below 2.0v. drv led mosfet gate driver ? connects to an external n-channel mosfet. src led mosfet current sense input - connects to the external n-channel mosfet source. ovp over voltage programming pin ? connects to a resistor divider between the output load and gnd to set the maximum output voltage. ovp has a voltage threshold of 1.2v lfb led current feedback input ? connects to a current s ense resistor between the led output load and gnd to set the led drive current. gnd common terminal for ground reference. brt led dimming signal input ? provides the internal reference, via an internal filter and gain resistor, allowing for a dynamic output led current adjustment that corresponds to the pwm input signal duty cycle. either a pwm signal or analog voltage can be used. t he actual brt pin voltage range is from v in to gnd. minimize the current sense resistor power dissipation by selecting a range for v brt = 0.0v to 0.5v. ref buffered reference output ? connected to the internal bandgap reference voltage of 1.2v. swx lcd bias inductor switch connection ? internally connec ted to the drain of a 28v n-channel mosfet. sw is high impedance in shutdown. fbx feedback input ? connect to a resistive divider network between the output and gnd to set the output voltage between v cc (in) and 25v. the feedback threshold is 1.29v. adjx lcd bias adjustment pwm signal input ? connect to an rc filter allowing for dynamic output voltage adjustment > 15%, corresponding to a varying duty cycle. either a pwm signal or analog voltage can be used. the adj input voltage range is from 0.9v to v in dc. the adjx pin should be connected to ground when the internal reference is used. lshdn led driver active-low shutdown input ? a logic low shut s down the led driver circuitry and reduces the supply current by 60 a (typ). pull lshdn high for normal operation. shdnx lcd bias active-low shutdown input ? a logic low shuts down the lcd bias circuitry and reduces the supply current by 60 a (typ). pull shdnx high for normal operation. cs current-sense amplifier input ? connecting a resistor between cs and gnd sets the peak inductor current limit. p p a a c c k k a a g g e e d d a a t t a a
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 4 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? electrical characteristics unless otherwise specified, the following specificati ons apply over the operat ing ambient temperature 0 c t a 70 c except where otherwise noted and the following test conditions: v in = 3v, lshdn = v in , 1 shdn = v in , 2 shdn = v in lx1745 parameter symbol test conditions min typ max units ` led driver v brt = 100mv 85 100 115 lfb threshold voltage v lfb v brt = 20mv 5 20 35 mv lfb input bias current i lfb v lfb = 100mv -100 100 na brt input voltage range v brt 0 vin v brt input bias current i brt brt = 100mv 60 na led driver shutdown input bias current i 1 shdn 0.0v 1 shdn vin -100 100 na current sense bias current i cs 4 a r cs = 0k 170 switch peak current i pk r cs = 2k 210 ma drv sink/source current v in = 5v, v drv = 3v 85 100 ma drv on-resistance r drv(on) v cc = 5v 12 15 maximum switch on-time t on v fb = 1v s minimum switch off-time t off v fb = 1v 200 300 410 ns ovp threshold voltage v ovp 1.15 1.21 1.26 reference voltage v ref 1.186 1.21 1.234 v ` lcd bias output voltage range v out 25 v fbx threshold voltage v fb 1.166 1.190 1.214 v fbx input current i fb v fb = 1.4v 200 na lcd bias shutdown input bias current i shdnx shdnx = gnd 100 na peak inductor current i lim t a = +25 c 330 ma internal nfet on-resistance r ds(on) i sw = 10ma, t a = +25 c, v in = 5v 1.1 switch pin leakage current i leak v sw = 25v 1.0 a switch on-time t on v fb = 1v s switch off-time t off v fb = 1v 150 400 ns adjx input voltage range v adjx 0.9 1.5 v adjx input bias current i adjx 0.3 1.0 a ` entire regulator operating voltage v in recommended operating range 1.6 6.0 v minimum start-up voltage t a = +25 c 1.6 v start-up voltage temperature coefficient -2 mv/ c shutdown high input voltage v shdnx v in = 2v 1.6 v shutdown low input voltage v shdnx v in = 2v 0.4 v v fbx = 1.4v, v lfb > v brt ? 0.1v 200 320 v fbx = 1.4v, v lfb > v brt ? 0.1v, v lshdn < 0.4v 0.35 1 v fbx = 1.4v, v lfb > v brt ? 0.1v, v 1 shdn < 0.4v 140 220 v fbx = 1.4v, v lfb > v brt ? 0.1v, v 2 shdn < 0.4v 80 120 quiescent current i q v 1 shdn < 0.4v, v 2 shdn < 0.4v, v lshdn < 0.4v 0.35 1 a e e l l e e c c t t r r i i c c a a l l s s
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 5 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? simplified block diagram control logic reference logic brt lfb shutdown logic lshdn cs driver gnd drv in src 2.5m 50pf shdnx control logic reference logic adjx fbx driver swx 2.5m 50pf ovp ref current limit control logic reference logic adjx driver swx current limit current limit fbx voltage reference 50pf 2.5m 4 a 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
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 6 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? application circuits c 1 4.7 f l 1 47 h 1206 case size lx1745 lfb cs drv in src r led 15 (typ) v bat = 1.6v to 6.0v i led = 20ma to 0ma ovp sw1 v lcd1 = v in to 25v fb1 - v lcd brt lshdn on off sw2 fb2 v lcd2 = v in to 25v ref adj1 shdn1 on off gnd adj2 shdn2 on off l 2 l 3 d 1 d 2 d 3 d 3 d 4 r 1 r 2 r 3 r 4 r 5 r 6 r cs (feedforward capacitor) figure 2 ? led driver with full-range dimming plus lcd bi as with contrast adjustment via pwm input a a p p p p l l i i c c a a t t i i o o n n s s
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 7 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? application note f unctional d escription the lx1745 is a triple output pulse frequency modulated (pfm) boost converter that is optimized for large step-up voltage applications like lcd biasing and led drive. operating in a pseudo-hysteretic mode with a fixed switch ?off time? of 300ns, co nverter switching is enabled when the feedback voltage (v fb ) falls below the bandgap reference voltage or the adj pin voltage managed by the reference logic block (see block diagram). when this occurs, the feedback comparator activates the switching logic, pulling the gate of the power mosfet high. this in turn connects the boost inductor to ground causing current to flow building up the energy stored in the inductor. the output remains ?on?, until the inductor current ramps up to the peak current level set either by the cs pin programming resistor (r cs ) in the case of the led dr iver or by an internal reference threshold for the lcd bias outputs. during this switch cycle, the load is powere d from energy stored in the output capacitor. once the peak inductor current value is achieved, the driver output is turned off, for the fixed off- time period of 300ns, allowing a portion of the energy stored in the inductor to be delivered to the load causing output voltage to rise at the input to the feedback circuit. if the voltage at the feedback pin is less than the internal reference at the end of the off-time period, the output switches the power mosfet ?on? and the inductor charging cycle repeats until the feedback pin voltage is greater than the internal reference. typical converter switching behavior is shown in figure 14. lcd b ias ? o utput v oltage p rogramming selecting the appropriate values for lcd bias output voltage divider (figure 3), conn ected to the feedback pin, programs the output voltage. lx1745 v bat = 1.6v to 6.0v swx v out r 1 r 2 fbx figure 3 ? lcd bias output voltage using a value between 40k and 75k for r 2 works well in most applications. r 1 can be determined by the following equation (where v ref = 1.19v nominal): ref ref out 2 1 v v - v r r = eq. 1 lcd b ias ? o utput v oltage a djustment the lx1745 allows for the dynamic adjustment of each of the voltage outputs via an adjustment pin (adjx). any voltage applied to the adjustment pin(s) works in conjunction with the internal reference logic. the lx1745 will automatically utilize the internal reference when no signal is detected or when the adjustment signal voltage is below approximately 0.6v. each of these pins includes an internal 50pf capacitor to ground (figure 4) that works w ith an external resistor to create a low-pass filter. this allows a direct pwm (f pwm 100khz) signal input to be used for the voltage adjustment signal. (consequently a dc bias signal can also be used). lx1745 adjx reference logic 50pf 2.5m r adjx_1 figure 4 ? lcd bias adjustment input different pwm signal levels can be accommodated by selecting a value for r pwm such that the filtered v adjx value is equal to the reference voltage (eq. 2) ? ? ? ? ? ? ? ? + ? ? = 1 _ pwm pwm adjx r m 5 . 2 m 5 . 2 cycle duty v v eq. 2 lx1745 adjx c adjx r adjx_1 r adjx_2 figure 5 ? lcd bias adjustment input filter ideally the resultant ripple on the adjx pin should be approximately 1% or 40db down from the nominal reference. when using a pwm with a frequency that is a a p p p p l l i i c c a a t t i i o o n n s s
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 8 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? application note less than 100khz, an external filter capacitor will be needed (figure 5). the value of c pwm is easily calculated based on the pwm frequency and r pwm_1 using the following equation. 1 _ pwm pwm pwm r f 50 c ? ? = eq. 3 where << m 5 . 2 r 1 _ pwm eq. 4 led d river ? o utput c urrent p rogramming maximum led current is easily programmed by choosing the appropriate value for r led (figure 6). it is recommended that a minimum value of 15 be used for this resistor in order to prevent noise coupling issues on the feedback line. although, alte rnate values can be calculated using the following equation: ) max ( led ) max ( brtx led i v r = eq. 5 c 1 4.7 f l 1 lx1745 lfb cs drv src r led 15 ovp brt d 1 r ovp_1 r ovp_2 r cs v bat = 1.6v to 6.0v c brt r brt_2 r brt_1 figure 6 ? led current programming led d river ? led b rightness a djustment the lx1745 features a full range dimming led driver. led current regulation is accomplished by using the applied brt pin voltage as the led current reference. this reference voltage, in conj unction with the led current setting resistor (r led ), sets the led output current. dimming can be accomplished in one of two ways: by applying a variable dc voltage, or by varying the duty cycle (dc) of a pwm control signal, directly to the brt pin. it is recommended that a maximum signal voltage of 300mv (v brt ) be used in order to minimize dissipative losses in the led current sense resistor (r led ). like the lcd bias adjustment (adjx) pins, the brt pin is connected to an in ternal 50pf capacitor to ground that works with an external resistor to create a low-pass filter, allowing the brt pin to driven directly by a pwm signal whose frequency is greater than 100khz. when this pin is driven by a pwm signal whose frequency is less than 100khz, an external filter capacitor is needed. this capacitor is selected such that the ripple component of the resultant voltage on the brt pin is less than 10% of the nominal input voltage. for pwm frequencies greater than 100khz, the external brt input resistor is calculated using the following equation. ? ? ? ? ? ? ? ? ? ? = ) max ( brt ) max ( brt max pwm 1 _ brt v v ) dc ( v m 5 . 2 r eq. 6 where v brt is the selected maximum led current sense feedback threshold. for pwm frequencies less than 100khz, the external brt input resistors and filter capacitor (figure 4) are calculated using the following equations. ? ? ? ? ? ? ? ? ? ? = ) max ( brt ) max ( brt max pwm 2 _ brt 1 _ brt v v ) dc ( v r r eq. 7 where r brt_2 is selected and v brt(max) is the selected maximum led current sense feedback threshold. ? ? ? ? ? ? ? ? ? + ? ? = 2 _ brt 1 _ brt 2 _ brt 1 _ brt pwm brt r r r r f 5 c eq. 8 where v ripple is selected to be 10% of v brt , and f pwm is the pwm signal frequency . d iode s election a schottky diode is recommended for most applications (e.g. microsemi ups5817). the low forward voltage drop and fast recovery time associat ed with this device supports the switching demands associated with this circuit topology. the designer is en couraged to consider the diode?s average and peak current ratings with respect to the application?s output and peak inductor current requirements. further, th e diode?s reverse breakdown voltage characteristic must be capable of withstanding 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
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 9 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? application note negative voltage transition that is greater than the output voltage. p ower m osfet s election the lx1745 can source up to 100ma of gate current. an logic level n-channel mosfet with a low turn on threshold voltage, low gate charge and low r ds(on) is required to optimize overall circuit performance. o ver v oltage p rotection p rogramming since the output of the led driver is a current mode configuration, it may be desirable to protect the output from an over-voltage condition in the event the load is removed or not present. the lx1745 includes an over voltage monitor that is easily programmed with two external resistors (figure 6). this feature eliminates the need for a zener diode clamp on the output. programming is accomplished by first selecting r ovp_2 and then calculating r ovp_1 using the following equation. ref ref ovp 2 _ ovp 1 _ ovp v v - v r r = eq. 9 where v ovp is the desired maximum voltage on the output. this voltage should be se lected to accommodate the maximum forward voltage of all the leds, over temperature, plus the maximum feedback voltage. conversely, it may also be selected according to the maximum v ds voltage of the output mosfet. i nductor c urrent l imit p rogramming setting of the peak inductor current limit is an important aspect of the pfm constant off-time architecture; it determines the maximum output power capability and has a marked effect on efficiency. it is recommended that the peak inductor current be set to approximately two times the expected maximum dc input current. this setting will minimize the inductor size, the input ripple current, and the output ripple voltage. care should be taken to use inductors that will not saturate at the peak inductor current level. the desired peak inductor current can be estimated by the following equation: in out pk v p 2 i ? ? = eq. 10 where p out is the total output power, is the expected conversion efficiency, and v in is the input voltage. from the calculated desired i pk an r cs resistance value can be chosen from the following equation: 6 pk cs 10 30 185 . 0 i r ? ? ? ? eq. 11 which is taken from the following graph (figure 7). 0 200 400 600 800 1000 0 5 10 15 20 r cs (k ) peak inductor current (ma) figure 7 ? peak current programming resistor this graph characterizes the relationship between peak inductor current, the inductance value, and the r cs programming resistor. i nductor s election an inductor value of 47 h has been show to yield very good results. choosing a lower value emphasizes peak current overshoot, effectiv ely raises the switching frequency, and increases the dissipative losses due to increased currents. o utput c apacitor s election output voltage ripple is a function of the several parameters: inductor value, output capacitance value, peak switch current, load current, input voltage, and the output voltage. all of these factors can be summarized by the following equation: ? ? ? ? ? ? ? ? ? + ? + + ? ? ? ? ? ? ? ? ? ? ? ? in f out out pk l sw in out out pk ripple v v v i i ) v v ( v 1 c i i l v eq. 12 where v l is the voltage drop across the inductor, v f is the forward voltage of the output catch diode, and v sw is the voltage drop across the power switch. v l +v sw can be approximated at 0.4v and v f can be approximated at 0.4v. a a p p p p l l i i c c a a t t i i o o n n s s
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 10 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? application note n egative lcd b ias g eneration for applications that require it, a negative bias can be easily generated using an inductorless charge pump consisting of only four add itional discrete components (figure 8). lx1745 v bat = 1.6v to 6.0v swx v out r 1 r 2 fbx - v out d 3 d 4 figure 8 ? negative bias generation this negative output is a mirror of the positive output voltage. however, it is unregulated. if a regulated negative bias is desired then this is also possible with some additional components. a low current shunt regulator (lx6431 or lx432) and a bipolor pass element can form a simple negative voltage ldo (figure 9). lx1745 v bat = 1.6v to 6.0v swx v out r 1 r 2 fbx d 3 d 4 v neg_lcd lx6431, lx432 r 3 r 4 r 5 figure 9 ? regulated negative bias r 3 is sized to meet the minimum shunt current required for regulation while r 4 and r 5 are calculated. if r 5 is selected to be 100k then r 4 is calculated using the following equation: ? ? ? ? ? ? ? ? + ? = 5 4 ref lcd _ neg r r 1 v v eq. 13 where v ref is a -2.5v in the case of the lx6431. f eed -f orward c apacitance improved efficiency and ripple performance can be achieved by placing a feed-f orward capacitor across the feedback resistor connected to the output (figure 2). a recommended value of 1nf should be used. pcb l ayout minimizing trace lengths from the ic to the inductor, diode, input and output capacitors, and feedback connection (i.e. pin 3) are typical considerations. moreover, the designer should maximize the dc input and output trace widths to accommodate peak current levels associated with this circuit. shdn shdn2 shdn1 lcd1 lcd2 led 0 0 1 1 0 0 0 1 1 1 1 0 1 0 1 1 0 1 1 1 1 1 1 1 1 1 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 table 1 ? enable logic a a p p p p l l i i c c a a t t i i o o n n s s
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 11 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? evaluation board table 2: input and output pin assignments name input/output range description vin 0 to 6v main power supply for outputs. gnd 0v common ground reference. adj1 apply a dc voltage or a pwm voltage to this pin to adjust the lcd1 output voltage. pwm inputs should be greater than 120hz. adj2 0 to vin-100mv apply a dc voltage or a pwm voltage to this pin to adjust the lcd2 output voltage. pwm inputs should be greater than 120hz. shdn pulled up to vin on board (10k ? ), ground to inhibit the led driver output (vout). shdn1 pulled up to vin on board (10k ? ), ground to inhibit the vlcd1. shdn2 0 to vin pulled up to vin on board (10k ? ), ground to inhibit the vlcd2. vlcd1 25v output voltage test point. programm ed for 18v output, adjustable up to 25v. -vlcd -25v output voltage mirror of vlcd1 vlcd2 25v output voltage test point. programm ed for 22v output, adjustable up to 25v. vout 25v led drive voltage probe point. fdbk 0 to vin led current sense feedback. brt 0 to 350mv apply a dc voltage or a pwm voltage to this pin to adjust the led current. pwm inputs should be greater than 120hz with a dc portion less than 350mv. ref 1.19v typ. buffered ic reference output. note: all pins are referenced to ground. a a p p p p l l i i c c a a t t i i o o n n s s
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 12 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? evaluation board table 3: jumper position assignments jumper position function ju1 n/a ju2 n/a ju3 n/a remove the factory installed jumper and insert a 4~6cm wire loop (optional) to observe the inductor current waveform using a current probe. ju4 n/a remove jumper to test open-circuit over-voltage protection implemented with r1 and r2 note: all pins are referenced to ground. table 4: factory installed component list ref part description c1 capacitor, 4.7 f, 1210, 6.3v c2, c5, c6 capacitor, 4.7 f, 1210, 35v c3, c7, c8 capacitor, 1000pf, 0805, 35v c4, c11 capacitor, (spare), see note 1 c9, c10, c12, c13 capacitor, 1 f, 0805, 35v cr1, cr2, cr3, cr4, cr5 microsemi ups5819, scho ttky, 1a, 40v, powermite led1, led2, led3, led4 microsemi upwledxx, led, optomite l1, l2, l3 inductor, 47 h, 480ma, smt q1 fdv303n mosfet, 30v, sot-23 r1, r5 resistor, 1m, 1/16w, 0805 r2, r6, r8 resistor, 75k, 1/16w, 0805 r3 resistor, 15, 1/16w, 0805 r4 resistor, 4.02k, 1/16w, 0805 r7 resistor, 1.25m, 1/16w, 0805 r9, r10, r11 resistor, 10k, 1/16w, 0805 r12, r13 resistor, 100k, 1/16w, 0805 u1 microsemi lx1745cpw boost controller notes 1. use these locations to insert addi tional input and/or output capacitance. a a p p p p l l i i c c a a t t i i o o n n s s
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 13 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? evaluation board r4 4.02k l1 47.0uh + c1 4.7uf 6.3v c3 1000pf r1 1m r2 72k r3 15 18v vlcd1 1 22v l2 l3 cr1 ups5819 cr2 ups5819 cr3 ups5819 shdn1 1 shdn2 1 vlcd2 1 + c5 4.7uf 35v + c6 4.7uf 35v + c4 spare c7 1000pf u1 lx1745 cs 15 adj1 2 brt 16 sw1 1 shdn1 3 vin 4 shdn2 9 ovp 17 shdn 5 drv 6 src 7 sw2 10 ledgnd 8 lfb 14 adj2 13 lcdgnd2 11 ref 18 fb2 12 lcdgnd1 20 fb1 19 c8 1000pf ju3 1 2 r5 1m r6 72k r7 1.25m r8 72k adj1 1 adj2 1 c13 1uf ref 1 r12 100k c12 1uf r13 100k ju2 1 2 ju1 1 2 gnd 1 vin 1 cr4 ups5819 cr5 ups5819 c9 1uf c10 1uf -vlcd 1 + c2 4.7uf 35v vout 1 fdbk 1 gnd 1 + c11 spare q1 fdv303n ju4 1 2 led 4 led 3 led 2 led 1 brt 1 shdn 1 r11 10k r10 10k r9 10k figure 10 ? lx1745eval evaluati on board schematic figure 11 ? lx1745eval evaluation board a a p p p p l l i i c c a a t t i i o o n n s s
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 14 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? vout versus vadj gate drive 0 5 10 15 20 25 30 00.511.52 adjustment signal voltage (vadjx) output voltage (v) figure 12 ? output voltage vs. adjustment signal threshold note: the lx1745 uses the internal voltage reference until the vadj signal exceeds 0.5v (typ). 0 1 2 3 4 5 6 0 20 40 60 80 100 120 140 160 drv current (ma) drv voltage (v) figure 13 ? gate drive voltage vs. drive current v in = 5v, t a = 25 c waveform efficiency figure 14 ? typical switching waveform ch1 ? swx voltage, ch2 ? output voltage, ch3 ? inductor current v in = 3.6v, v out = 18v, i out = 9ma 50% 55% 60% 65% 70% 75% 80% 85% 90% 0 5 10 15 20 25 output current (ma) efficiency figure 15 ? led driver (upper) and lcd bias efficiency v in = 5v, four leds, l = 47 h, r cs = 4k v in = 3.6v, v out = 5.5v, l = 47 h c c h h a a r r t t s s
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 15 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 tm ? package dimensions pw 20-pin thin small shrink outline package (tssop) c 1 2 3 e d e1 e a2 a1 a l b seating plane 1 m illimeters i nches dim min max min max a - 1.10 - 0.043 a1 0.05 0.15 0.002 0.006 a2 0.80 1.05 0.031 0.041 b 0.19 0.30 0.007 0.012 c 0.09 0.20 0.004 0.008 d 6.40 6.60 0.252 0.260 e 6.25 6.55 0.246 0.258 e1 4.30 4.50 0.169 0.177 e 0.65 bsc 0.026 bsc l 0.45 0.75 0.018 0.030 1 0 8 0 8 *lc - 0.10 - 0.004 * lead coplanarity 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
lx1745 p roduction d atasheet microsemi integrated products division 11861 western avenue, garden grove, ca. 92841, 714-898-8121, fax: 714-893-2570 page 16 www. microsemi . com triple output boost ? led driver / lcd bias copyright ? 2000 rev. 1.2, 2006-02-27 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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