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LT3465A 1 3465ai , ltc and lt are registered trademarks of linear technology corporation. n inherently matched led current n drives up to six leds from a 3.6v supply n no external schottky diode required n open led protection n high efficiency: 79% typical n requires only 0.22 m f output capacitor n switching frequency above am broadcast band n low profile (<1mm) sot-23 packaging 2.4mhz white led step-up converter with built-in schottky in thinsot tm august 2003 n cellular phones n pdas, handheld computers n digital cameras n mp3 players n gps receivers descriptio u features applicatio s u typical applicatio u information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. final electrical specifications the lt 3465a is a step-up dc/dc converter designed to drive up to six leds in series from a li-ion cell. series connection of the leds provides identical led currents and eliminates the need for ballast resistors. this device integrates the schottky diode required externally on com- peting devices. additional features include output voltage limiting when leds are disconnected, one-pin shutdown and dimming control. the LT3465A switches at 2.4mhz, allowing the use of tiny external components. constant frequency switching re- sults in low input noise and a small output capacitor. just 0.22 m f is required for 3-, 4- or 5-led applications. the LT3465A is available in a low profile (<1mm) 6-lead sot-23 package. thinsot is a trademark of linear technology corporation. figure 1. li-ion powered driver for four white leds sw v out v in LT3465A ctrl 3465a f01a r1 10 c1 1 f c2 0.22 f c1, c2: x5r or x7r dielectric l1: murata lqh32cn220 l1 22 h 3v to 5v shutdown and dimming control fb gnd conversion efficiency led current (ma) 0 efficiency (%) 20 3465a f01b 5 10 15 80 78 76 74 72 70 68 66 64 62 60 v in = 3.6v
LT3465A 2 3465ai input voltage (v in ) ................................................. 16v sw voltage ............................................................. 36v fb voltage ................................................................ 2v ctrl voltage .......................................................... 10v operating temperature range (note 2) .. C 40 c to 85 c maximum junction temperature ......................... 125 c storage temperature range ................ C 65 c to 150 c lead temperature (soldering, 10 sec)................. 300 c order part number (note 1) absolute axi u rati gs w ww u package/order i for atio uu w consult ltc marketing for parts specified with wider operating temperature ranges. LT3465Aes6 t jmax = 125 c, q ja = 256 c/w in free air q ja = 120 c on board over ground plane q jc = 102 c/w the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 3v, v ctrl = 3v, unless otherwise noted. parameter conditions min typ max units minimum operating voltage 2.7 v maximum operating voltage 16 v feedback voltage 0 c t a 85 c 188 200 212 mv fb pin bias current 10 35 100 na supply current not switching 1.9 2.6 3.3 ma ctrl = 0v 2.0 3.2 5.0 m a switching frequency 1.8 2.4 2.8 mhz maximum duty cycle l 90 93 % switch current limit l 225 340 ma switch v cesat i sw = 250ma 300 mv switch leakage current v sw = 5v 0.01 5 m a v ctrl for full led current 1.8 v v ctrl to shut down device 50 mv ctrl pin bias current 48 60 72 m a t a = 85 c 405060 m a t a = C40 c 607590 m a schottky forward drop i d = 150ma 0.7 v schottky leakage current v r = 30v 4 m a electrical characteristics v out 1 gnd 2 top view s6 package 6-lead plastic tsot-23 fb 3 6 sw 5 v in 4 ctrl s6 part marking ltaft note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: the LT3465Ae is guaranteed to meet performance specifications from 0 c to 70 c. specifications over the C40 c to 85 c operating temperature range are assured by design, characterization and correlation with statistical process controls.
LT3465A 3 3465ai typical perfor a ce characteristics uw switch saturation voltage (v cesat ) schottky forward voltage drop shutdown quiescent current (ctrl = 0v) switch current (ma) 0 0 switch saturation voltage (mv) 50 150 200 250 200 450 3465 g01 100 100 50 250 300 150 350 300 350 400 t a = 25 c schottky forward drop (mv) 0 0 schottky forward current (ma) 50 100 150 200 300 200 400 600 800 3465 g02 1000 1200 250 t a = 25 c v in (v) 2 i q ( a) 12 15 18 8 14 3465 g03 9 6 3 0 4 6 10 12 21 24 27 30 16 t a = 25 c v fb vs v ctrl open-circuit output clamp voltage control voltage (v) 0 feedback voltage (mv) 100 150 2 3465 g04 50 0 0.5 1 1.5 250 200 t a = 25 c input voltage (v) 2 20 25 35 812 3465 g05 15 10 46 10 14 16 5 0 30 output clamp voltage (v) t a = 25 c input current in output open circuit switching waveforms v sw 10v/div i l 50ma/div v out 50mv/div v in = 3.6v 100ns/div 3465 g07 4 leds 20ma, 22 m h switching frequency temperature ( c) ?0 190 feedback voltage (mv) 192 196 198 200 210 204 ?0 30 50 3465 g09 194 206 208 202 ?0 10 70 90 feedback voltage input voltage (v) 2.0 input current (ma) 5 4 3 2 1 0 2.5 3.0 3.5 4.0 3465 g06 4.5 5.0 temperature ( c) ?0 switching frequency (mhz) 3.0 2.5 2.0 1.5 1.0 0.5 0 0 50 100 3465 g08
LT3465A 4 3465ai typical perfor a ce characteristics uw quiescent current (ctrl = 3v) v in (v) 0 0 i q (ma) 0.5 1.0 1.5 2.0 2.5 3.0 5101520 3465 g10 ?0 c 25 c 100 c duty cycle (%) 0 current limit (ma) 150 200 250 60 100 3465 g11 100 50 0 20 40 80 300 350 400 ?0 c 25 c 100 c switching current limit v in = 3.6v, 4 leds uu u pi fu ctio s v out (pin 1): output pin. connect to output capacitor and leds. minimize trace between this pin and output capaci- tor to reduce emi. gnd (pin 2): ground pin. connect directly to local ground plane. fb (pin 3): feedback pin. reference voltage is 200mv. connect leds and a resistor at this pin. led current is determined by the resistance and ctrl pin voltage: i mv r when v v i v r when v v led fb ctrl led ctrl fb ctrl ?> ?< 200 18 5 1 . (1) ctrl (pin 4): dimming control and shutdown pin. ground this pin to shut down the device. when v ctrl is greater than about 1.8v, full-scale led current is generated. when v ctrl is less than 1v, led current is reduced. v in (pin 5): input supply pin. must be locally bypassed with a 1 m f x5r or x7r type ceramic capacitor. sw (pin 6): switch pin. connect inductor here. temperature ( c) ?0 schottky leakage current ( a) 3 4 v r = 25 v r = 16 v r = 10 5 3465 g13 2 1 0 050 6 7 8 100 schottky leakage current temperature ( c) ?0 efficiency (%) 3465a g12 0 50 100 80 79 78 77 76 75 74 73 72 71 70 20ma 15ma 10ma
LT3465A 5 3465ai block diagra w + + + rq s 0.2 w sw driver comparator 2 ctrl 4 6 v out v in 3 fb 200mv 5 + s ramp generator r c 10k 40k c c 2.4mhz oscillator gnd 3465a f02 q1 a2 a1 v ref 1.25v 1 figure 2. LT3465A block diagram applicatio s i for atio wu uu operation the LT3465A uses a constant frequency, current mode control scheme to provide excellent line and load regula- tion. operation can be best understood by referring to the block diagram in figure 2. at the start of each oscillator cycle, the sr latch is set, which turns on the power switch q1. a voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the pwm comparator a2. when this voltage exceeds the level at the negative input of a2, the sr latch is reset turning off the power switch. the level at the negative input of a2 is set by the error amplifier a1, and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 200mv. in this manner, the error amplifier sets the correct peak current level to keep the output in regulation. if the error amplifiers output increases, more current is delivered to the output; if it decreases, less current is delivered. the ctrl pin voltage is used to adjust the reference voltage. minimum output current t he LT3465A can drive a 3-led string at 0.2ma led current without pulse skipping. as current is further reduced, the device may begin skipping pulses. this will result in some low frequency ripple, although the led current remains regulated on an average basis down to zero. the photo in figure 3 details circuit operation driving three white leds at a 0.2ma load. peak inductor current is less than 30ma and the regulator operates in discontinuous mode, meaning the inductor current reaches zero during the discharge phase. after the induc- tor current reaches zero, the sw pin exhibits ringing due to the lc tank circuit formed by the inductor in combina- tion with switch and diode capacitance. this ringing is not harmful; far less spectral energy is contained in the ringing than in the switch transitions. the ringing can be damped by application of a 300 w resistor across the inductor, although this will degrade efficiency. v sw 5v/div i l 20ma/div v out 10mv/div v in = 4.2v 0.1 m s/div 3465a f03 i led = 0.2ma 3 leds figure 3. switching waveforms
LT3465A 6 3465ai applicatio s i for atio wu uu inductor selection a 22 m h or 10 m h inductor is recommended for most LT3465A applications. although small size and high effi- ciency are major concerns, the inductor should have low core losses at 1.2mhz and low dcr (copper wire resis- tance). some inductors in this category with small size are listed in table 1. the efficiency comparison of different inductors is shown in figure 4. table 1. recommended inductors part current rating number dcr ( w ) (ma) manufacturer lqh32cn220 0.71 250 murata 814-237-1431 www.murata.com eljpc220kf 4.0 160 panasonic 714-373-7334 www.panasonic.com cdrh3d16-220 0.53 350 sumida 847-956-0666 www.sumida.com lb2012b220m 1.7 75 taiyo yuden 408-573-4150 www.t-yuden.com lem2520-220 5.5 125 taiyo yuden 408-573-4150 www.t-yuden.com capacitor selection the small size of ceramic capacitors makes them ideal for LT3465A applications. x5r and x7r types are recom- mended because they retain their capacitance over wider voltage and temperature ranges than other types such as y5v or z5u. a 1 m f input capacitor and a 0.22 m f output capacitor are sufficient for most LT3465A applications. table 2. recommended ceramic capacitor manufacturers manufacturer phone url taiyo yuden 408-573-4150 www.t-yuden.com murata 814-237-1431 www.murata.com kemet 408-986-0424 www.kemet.com inrush current the LT3465A has a built-in schottky diode. when supply voltage is applied to the v in pin, the voltage difference between v in and v out generates inrush current flowing from input through the inductor and the schottky diode to charge the output capacitor to v in . the maximum current the schottky diode in the LT3465A can sustain is 1a. the selection of inductor and capacitor value should ensure the peak of the inrush current to be below 1a. the peak inrush current can be calculated as follows: i v l aa r l lc r l p in = ? ? ? ? ? ? ? ? ? ? ? ? = + = + () . exp tan sin tan . . 06 15 2 1 15 4 2 2 w a w w a w a a w where l is the inductance, r is the resistance of the inductor and c is the output capacitance. for low dcr inductors, which is usually the case for this application, the peak inrush current can be simplified as follows: i v l p in = ? ? ? ? . exp 06 2 w a w p figure 4. efficiency comparison of different inductors led current (ma) 0 70 75 15 3465 f04 65 60 510 20 55 50 80 efficiency (%) v in = 3.6v 4 leds murata lqh32cn220 murata lqh32cn100 murata lqh2mcn220 toko d312-220 toko d312-100 taiyo yuden lb2012b220
LT3465A 7 3465ai table 3 gives inrush peak currents for some component selections. table 3. inrush peak current v in (v) r ( w )l ( m h) c ( m f) i p (a) 5 0.5 22 0.22 0.38 5 0.5 22 1 0.70 3.6 0.5 22 0.22 0.26 5 0.5 33 1 0.60 led current and dimming control the led current is controlled by the feedback resistor (r1 in figure 1) and the feedback reference voltage. i led = v fb /r fb the ctrl pin sets the feedback reference voltage as shown in the typical performance characteristics. when ctrl is at 1.8v or more, the feedback reference is 200mv, which results in full-scale led current. the ctrl pin can be used as a dimming control when its voltage is between 200mv to 1.5v. to maintain led current accuracy, a 1% or better resistor for r1 is recommended. the formula and table for r fb selection are shown below: r fb = 200mv/i ledf where i ledf is full-scale led current table 4. r fb resistor value selection i led (ma) r1 ( w ) 5 40.2 10 20.0 15 13.3 20 10.0 dimming using filtered pwm dimming can be realized by using an rc filter in front of the ctrl pin to filter a pwm signal, as depicted in figure 5. the filtered pwm signal is equivalent to a constant volt- age. the time constant r1 ? c1 should be much lower than the frequency of the pwm signal. additionally, r1 should be small compared to the 50k w impedance of the ctrl pin. suggested values are shown in figure 5. applicatio s i for atio wu uu dimming using direct pwm unlike the lt3465, the LT3465A does not have internal soft-start. although the input current is higher during start-up, the absence of soft-start allows the ctrl pin to be directly driven with a pwm signal for dimming. a zero percent duty cycle sets the led current to zero, while 100% duty cycle sets it to full current. average led current increases proportionally with the duty cycle of the pwm signal. pwm frequency should be between 1khz and 10khz for best performance. the pwm signal should be at least 1.8v in magnitude; lower voltage will lower the feedback voltage as shown in equation 1. waveforms are shown for a 1khz pwm and 10khz pwm signal in figures 6a and 6b respectively. lt3465 ctrl 3465 f06 pwm c1 100nf r1 5k figure 5. dimming control using a filtered pwm signal figure 6a. figure 6b. fb 100mv/div ctrl 2v/div 200 m s/div (1khz) 3465a f06a fb 100mv/div ctrl 2v/div 20 m s/div (10khz) 3465a f06b LT3465A ctrl pwm
LT3465A 8 3465ai applicatio s i for atio wu uu figure 7. recommended component placement open circuit protection the LT3465A has an internal open-circuit protection cir- cuit. when the leds are disconnected from the circuit or fail open, v out is clamped at 30v. the LT3465A will then switch at a low frequency, minimizing input current. v out and input current during open circuit are shown in the typical performance characteristics. board layout consideration as with all switching regulators, careful attention must be paid to the pcb board layout and component placement. to maximize efficiency, switch rise and fall times are made as short as possible. to prevent electromagnetic interfer- ence (emi) problems, proper layout of the high frequency 1 c out l r fb 2 3 6 5 4 c in gnd 3465 f07 v in ctrl switching path is essential. place c out next to the v out pin. always use a ground plane under the switching regulator to minimize interplane coupling. in addition, the ground connection for the feedback resistor r1 should be tied directly to the gnd pin and not shared with any other component, ensuring a clean, noise-free connection. rec- ommended component placement is shown in figure 7. start-up input current as previously mentioned, the LT3465A does not have an internal soft-start circuit. inrush current can therefore rise to approximately 400ma as shown in figure 8 when driving 4 leds. the lt3465 has an internal soft-start circuit and is recommended if inrush current must be minimized. figure 8. fb 200mv/div ctrl 2v/div 50 m s/div 3465a f06b i in 200mv/div
LT3465A 9 3465ai sw v out v in LT3465A ctrl 3465 ta02a r1 10 c in 1 f c out 0.22 f l1 22 h 3v to 5v fb gnd c in : taiyo yuden jmk107bj105 c out : avx 0603yd224 l1: murata lqh32cn220 li-ion to two white leds sw v out v in LT3465A ctrl 3465 ta01a r1 4 c in 1 f c out 1 f c in : taiyo yuden jmk107bj105 c out : avx 0603zd105 l1: murata lqh32cn220 l1 22 h 3v to 5v fb gnd li-ion to three white leds led current (ma) 0 efficiency (%) 75 80 85 40 3465 ta01b 70 65 60 55 50 10 20 30 50 v in = 3.6v 2 leds led current (ma) 0 efficiency (%) 75 80 85 3465 ta02b 70 65 60 55 50 5 10 15 20 v in = 3.6v 3 leds typical applicatio s u
LT3465A 10 3465ai typical applicatio s u li-ion to five white leds sw v out v in LT3465A ctrl 3465 ta03a r1 10 c in 1 f c out 0.22 f l1 22 h 3v to 5v fb gnd c in : taiyo yuden jmk107bj105 c out : taiyo yuden gmk212bj224 l1: murata lqh32cn220 led current (ma) 0 efficiency (%) 75 80 3465 ta03b 70 65 60 55 50 5 10 15 20 v in = 3.6v 5 leds
LT3465A 11 3465ai u package descriptio s6 package 6-lead plastic tsot-23 (reference ltc dwg # 05-08-1636) 1.50 ?1.75 (note 4) 2.80 bsc 0.30 ?0.45 6 plcs (note 3) datum ? 0.09 ?0.20 (note 3) s6 tsot-23 0302 2.90 bsc (note 4) 0.95 bsc 1.90 bsc 0.80 ?0.90 1.00 max 0.01 ?0.10 0.20 bsc 0.30 ?0.50 ref pin one id note: 1. dimensions are in millimeters 2. drawing not to scale 3. dimensions are inclusive of plating 4. dimensions are exclusive of mold flash and metal burr 5. mold flash shall not exceed 0.254mm 6. jedec package reference is mo-193 3.85 max 0.62 max 0.95 ref recommended solder pad layout per ipc calculator 1.4 min 2.62 ref 1.22 ref
LT3465A 12 3465ai linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear.com ? linear technology corporation 2003 li-ion to six white leds sw v out v in LT3465A ctrl 3465 ta04a r1 10 c in 1 f c out 0.47 f l1 22 h 3v to 5v fb gnd c in : taiyo yuden jmk107bj105 c out : tdk 2012x7r1e474k l1: murata lqh32cn220 lt/tp 0803 1.5k ? printed in usa related parts part number description comments lt1618 constant current, constant voltage, 1.4mhz, high efficiency up to 16 white leds, v in : 1.6v to 18v, v out(max) : 34v, i q : 1.8ma, boost regulator i sd : <1 m a, 10-lead ms package lt1932 constant current, 1.2mhz, high efficiency white led up to 8 white leds, v in : 1v to 10v, v out(max) : 34v, i q : 1.2ma, boost regulator i sd : <1 m a, thinsot package lt1937 constant current, 1.2mhz, high efficiency white led up to 4 white leds, v in : 2.5v to 10v, v out(max) : 34v, i q : 1.9ma, boost regulator i sd : <1 m a, thinsot, sc70 packages ltc ? 3200-5 low noise, 2mhz, regulated charge pump white led driver up to 6 white leds, v in : 2.7v to 4.5v, i q : 8ma, i sd : <1 m a, thinsot package ltc3200 low noise, 2mhz, regulated charge pump white led driver up to 6 white leds, v in : 2.7v to 4.5v, i q : 8ma, i sd : <1 m a, 10-lead ms package ltc3201 low noise, 1.7mhz, regulated charge pump white led driver up to 6 white leds, v in : 2.7v to 4.5v, i q : 6.5ma, i sd : <1 m a, 10-lead ms package ltc3202 low noise, 1.5mhz, regulated charge pump white led driver up to 8 white leds, v in : 2.7v to 4.5v, i q : 5ma, i sd : <1 m a, 10-lead ms package ltc3404 600ma (i out ), 1.4mhz synchronous step-down 95% efficiency, v in : 2.7v to 6v, v out(min) : 0.8v, i q : 10 m a, i sd : <1 m a, dc/dc converter ms8 package ltc3405 300ma (i out ), 1.5mhz synchronous step-down 95% efficiency, v in : 2.7v to 6v, v out(min) : 0.8v, i q : 20 m a, i sd : <1 m a, ltc3405a dc/dc converters thinsot package ltc3406 600ma (i out ), 1.5mhz synchronous step-down 95% efficiency, v in : 2.5v to 5.5v, v out(min) : 0.6v, i q : 20 m a, ltc3406b dc/dc converters i sd : <1 m a, thinsot package lt3407 dual 600ma (i out ), 1.5mhz synchronous step-down 96% efficiency, v in : 2.5v to 5.5v, v out(min) : 0.6v, i q : 40 m a, dc/dc converter i sd : <1 m a, ms package ltc3412 2.5a (i out ), 4mhz synchronous step-down dc/dc converter 95% efficiency, v in : 2.5v to 5.5v, v out(min) : 0.8v, i q : 60 m a, i sd : <1 m a, tssop16e package ltc3440 600ma (i out ), 2mhz synchronous buck-boost 95% efficiency, v in : 2.5v to 5.5v, v out(min) : 2.5v, i q : 25 m a, dc/dc converter i sd : <1 m a, 10-lead ms package ltc3465 constant current, 1.2mhz, high efficiency white led up to 5 white leds, v in : 2.7v to 16v, i q : 1.9a, boost regulator i sd : <1 m a, thinsot package typical applicatio u led current (ma) 0 efficiency (%) 75 80 3465 ta04b 70 65 60 55 50 5 10 15 20 v in = 3.6v 6 leds

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