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lt3460/lt3460-1 1 3460fb typical application features applications description 1.3 mhz/650khz step-up dc/dc converter in sc70, thinsot and dfn the lt ? 3460/lt3460-1 are general purpose step-up dc/ dc converters. the lt3460/lt3460-1 switch at 1.3mhz/ 650khz, allowing the use of tiny, low cost and low height capacitors and inductors. the constant frequency results in low, predictable output noise that is easy to ? lter. the high voltage switches in the lt3460/lt3460-1 are rated at 38v, making the device ideal for boost converters up to 36v. the lt3460 can generate 12v at up to 70ma from a 5v supply. the low 1ma quiescent current and 650khz switching frequency of lt3460-1 make it ideal for lower current applications. the lt3460 is available in sc70 and sot-23 packages. the lt3460-1 is available in sc70 and 2mm 2mm dfn packages. 5v to 12v, 70ma step-up dc/dc converter n 1.3mhz (lt3460) switching frequency n 650khz (lt3460-1) switching frequency n high output voltage: up to 36v n 300ma integrated switch (lt3460) n 180ma integrated switch (lt3460-1) n wide input range: 2.5v to 16v n uses small surface mount components n low shutdown current: <1a n low pro? le (1mm) sc70 (lt3460 and lt3460-1), sot-23 (thinsot?) (lt3460) and 2mm 2mm dfn (lt3460-1) packages n digital cameras n ccd bias supply n xdsl power supply n tft-lcd bias supply n local 5v or 12v supply n medical diagnostic equipment n battery backup l , lt, ltc and ltm are registered trademarks of linear technology corporation. thinsot is a trademark of linear technology corporation. all other trademarks are the property of their respective owners. ef? ciency switching waveforms load current (ma) 0 efficiency (%) 90 85 80 75 70 65 60 20 40 60 80 3460 f01a 0.2s/div 3460 f01b i l 100ma/div v sw 5v/div off on v in 5v 22h 130k 15k 1f 22pf 4.7f v out 12v 70ma v in sw fb shdn gnd lt3460 3460 f01
lt3460/lt3460-1 2 3460fb absolute maximum ratings input voltage (v in ) ....................................................16v sw voltage ...............................................................38v fb voltage ...................................................................5v shdn voltage ...........................................................16v (note 1) 5 v in 4 shdn sw 1 top view s5 package 5-lead plastic tsot-23 gnd 2 fb 3 t jmax = 125c,
lt3460/lt3460-1 3 3460fb electrical characteristics note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c, v in = 3v, v shdn = 3v, unless otherwise noted. parameter conditions min typ max min typ max units minimum operating voltage 2.5 2.5 v maximum operating voltage 16 16 v feedback voltage l 1.235 1.225 1.255 1.275 1.280 1.235 1.225 1.255 1.275 1.280 v v feedback line regulation 2.5v < v in < 16v 0.015 0.015 %/v fb pin bias current l 5 25 80 0 25 80 na supply current shdn = 0v 2.0 0.1 3.0 0.5 1.0 0.1 1.5 0.5 ma a switching frequency 1.0 1.3 1.7 0.35 0.65 1.0 mhz maximum duty cycle 85 90 80 90 % switch current limit 300 420 600 180 260 380 ma switch v cesat i sw = 250ma (lt3460), i sw = 100ma (lt3460-1) 320 450 220 350 mv switch leakage current v sw = 5v 0.01 1 0.01 1 a shdn voltage high 1.5 1.5 v shdn voltage low 0.4 0.4 v shdn pin bias current 40 15 a note 2: the lt3460e/lt3460-1e is guaranteed to meet speci? cations from 0c to 70c. speci? cations over the C40c to 85c operating temperature range are assured by design, characterization and correlation with statistical process controls. lt3460 lt3460-1 typical performance characteristics quiescent current switching frequency shdn pin bias current v in (v) 0 2.0 10 3460 g01 1.5 0.5 1.0 5 15 0 i q (ma) 2.5 100c 25c C50c lt3460 lt3460-1 temperature (c) C50 0.8 1.0 1.2 25 75 3460 g02 0.6 0.4 C25 0 50 100 0.2 0 switching frequency (mhz) 1.4 lt3460 lt3460-1 temperature (c) C50 250 300 350 25 75 3460 g03 200 150 100 C25 0 50 100 50 0 shdn pin bias current (a) 400 shdn = 3v (lt3460) shdn = 16v (lt3460) shdn = 16v (lt3460-1) shdn = 3v (lt3460-1)
lt3460/lt3460-1 4 3460fb (thinsot/sc70/dfn packages) sw (pin 1/pin 1/pin 3): switch pin. connect inductor/diode here. minimize trace at this pin to reduce emi. gnd (pin 2/pins 2 and 5/exposed pad pin 7): ground pin. tie directly to local ground plane. fb (pin 3/pin 3/pin 1): feedback pin. reference voltage is 1.255v. connect resistor divider tap here. minimize trace area at fb. set v out according to v out = 1.255v (1 + r1/r2). shdn (pin 4/pin 4/pin 6): shutdown pin. tie to 1.5v or higher to enable device; 0.4v or less to disable device. also functions as soft-start. use rc ? lter (47k, 47nf typ) as shown in figure 1. v in (pin 5/pin 6/pin 4): input supply pin. must be locally bypassed. nc (na/na/pins 2, 5): no-connects. these pins are not connected to internal circuitry. they should be tied to ground to improve thermal and electrical performance. typical performance characteristics feedback bias current feedback voltage temperature (c) C50 15 20 25 25 75 3460 g04 10 5 C25 0 50 100 0 feedback bias current (na) 30 temperature (c) C50 1.255 25 75 3460 g05 1.250 1.245 C25 0 50 100 1.240 v fb (v) 1.260 switch saturation voltage (v cesat ) current limit vs duty cycle temperature (c) C50 250 300 350 25 75 3460 g06 200 150 100 C25 0 50 100 50 0 v cesat (mv) 400 (lt3460) (lt3460) (lt3460) (lt3460-1) i c = 100ma i c = 200ma i c = 250ma i c = 50ma duty cycle 0 250 300 350 0.6 3460 g07 200 150 100 0.2 0.4 0.8 1.0 50 0 current limit (ma) 450 400 lt3460 lt3460-1 pin functions
lt3460/lt3460-1 5 3460fb block diagram figure 1. block diagram, lt3460 C + C + C + v out r1 (external) r2 (external) r s (external) c s (external) fb shutdown shdn ramp generator 1.255v reference 1.3mhz oscillator r s q a1 a2 comparator driver r c c c sw q1 0.1 gnd v in fb 3460 bd r s , c s optional soft-start components operation the lt3460/lt3460-1 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. operation can be best understood by referring to the block diagram in figure 1. 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 ampli? er a1, and is simply an ampli? ed version of the difference between the feedback voltage and the reference voltage of 1.255v. in this manner, the error ampli? er sets the correct peak current level to keep the output in regulation. if the error ampli? ers output increases, more current is delivered to the output; if it decreases, less current is delivered. feedback loop compensation the lt3460/lt3460-1 has an internal feedback compensa- tion network as shown in figure 1 (r c and c c ). however, because the small signal characteristics of a boost converter change with operation conditions, the internal compensa- tion network cannot satisfy all applications. a properly designed external feed forward capacitor from v out to fb (c f in figure 2) will correct the loop compensation for most applications. the lt3460/lt3460-1 uses peak current mode control. the current feedback makes the inductor very similar to a current source in the medium frequency range. the power stage transfer function in the medium frequency range can be approximated as: g p(s) = k1 s?c 2 , where c2 is the output capacitance, and k1 is a constant based on the operating point of the converter. in continuous current mode, k1 increases as the duty cycle decreases. the internal compensation network r c , c c can be ap- proximated as follows in medium frequency range: g c(s) = k2 ? s?r c ?c c + 1 s?c c the zero f z = 1 2? ?r c ?c c is about 70khz.
lt3460/lt3460-1 6 3460fb operation figure 3 frequency (khz) phase gain 1 gain (db) 60 50 40 30 20 phase (deg) 10 0 C10 C20 C30 C40 90 45 0 C45 C90 C135 C180 C225 C270 C315 C360 10 100 1000 3460 f03 figure 4 60 50 40 30 20 10 0 C10 C20 C30 C40 phase (deg) 90 45 0 C45 C90 C135 C180 C225 C270 C315 C360 frequency (khz) phase gain 1 gain (db) 10 100 1000 3460 f04 the feedback loop gain t(s) = k3 ? g p (s) ? g c (s). if it crosses over 0db far before f z , the phase margin will be small. figure 3 is the bode plot of the feedback loop gain measured from the converter shown in figure 2 without the feedforward capacitor c f . the result agrees with the previous discussion: phase margin of about 20 is insuf? cient. in order to improve the phase margin, a feed-forward capacitor c f in figure 2 can be used. without the feed-forward capacitor, the transfer function from v out to fb is: fb v ou t = r1 r1 + r 2 with the feed-forward capacitor c f , the transfer function becomes: fb v ou t = r1 r1 + r 2 ? s?r2?c f + 1 s? r1? r2 r1 + r 2 ?c f + 1 the feed-forward capacitor c f generates a zero and a pole. the zero always appears before the pole. the frequency distance between the zero and the pole is determined only by the ratio between v out and fb. to give maximum phase margin, c f should be chosen so that the midpoint frequency between the zero and the pole is at the cross over frequency. with c f = 20pf, the feedback loop bode plot is reshaped as shown in figure 4. the phase margin is about 60. figure 2. 5v to 12v step-up converter off on v in 5v l1 22h d1 r2 130k r1 15k c2 1f c f 22pf c1 4.7f v out 12v 70ma 51 3 2 4 v in sw fb shdn gnd lt3460 c1: taiyo yuden x5r jmk212bj475kg c2: taiyo yuden x5r emk316bj105 d1: central semiconductor cmdsh2-3 l1: murata lqh32cn-220 or equivalent 3460 f02 the feed-forward capacitor increases the gain at high frequency. the feedback loop therefore needs to have enough attenuation at the switching frequency to reject the switching noise. additional internal compensation components have taken this into consideration. for most of the applications of lt3460/lt3460-1, the output capacitor esr zero is at very high frequency and can be ignored. if a low frequency esr zero exists, for example, when a high-esr tantalum capacitor is used at the output, the phase margin may be enough even without a feed-forward capacitor. in these cases, the feed-forward capacitor should not be added because it may cause the feedback loop to not have enough attenuation at the switching frequency.
lt3460/lt3460-1 7 3460fb operation layout hints the high speed operation of the lt3460/lt3460-1 demands careful attention to board layout. you will not get adver- tised performance with careless layout. figure 5 shows the recommended component placement. figure 5 typical applications r1 r2 gnd c f c2 l1 d1 c1 v out v in shutdown + + 3460 f05a (sot-23 package) r1 r2 gnd c f c2 l1 d1 c1 v out v in shutdown 3460 f05b + + (sc70 package) 3460 f05c (6-lead 2mm 2mm dfn package) 4 5 7 6 3 2 1 d1 l1 c o c in r1 r2 c f v in gnd shdn v out 5v to 12v step-up converter ef? ciency shdn v in 5v l1 22h d1 130k 15k c2 1f 22pf c1 4.7f v out 12v 70ma 51 3 2 4 c1: taiyo yuden x5r jmk212bj475 c2: taiyo yuden x5r emk212bj105 d1: central semiconductor cmdsh2-3 l1: murata lqh32cn-220 or equivalent 3460 ta01 v in sw fb shdn gnd lt3460 load current (ma) 0 efficiency (%) 90 85 80 75 70 65 60 20 40 60 80 3460 ta01a
lt3460/lt3460-1 8 3460fb typical applications load step response input current and output voltage 5v to 12v with soft-start circuit 100s/div 3460 ta01b 58ma 34ma v out 100mv/div i load v in 5v v out 12v 70ma l1 22h d1 130k 47k control signal 15k c2 1f 16v 22pf 47nf c1 4.7f v in sw fb shdn gnd lt3460 3460 ta02 c1: taiyo yuden x5r jmk212bj475 c2: taiyo yuden x5r emk212bj105 d1: central semiconductor cmdsh2-3 l1: murata lqh32cn-220 or equivalent 500s/div 3460 ta02b control signal 2v/div i in 100ma/div v 0 5v/div 5v to 12v step-up converter ef? ciency v in 3.3v l1 22h d1 130k 15k c2 1f 16v 22pf c1 4.7f v in sw fb shdn gnd lt3460 3460 ta03 c1: taiyo yuden x5r jmk212bj475 c2: taiyo yuden x5r emk212bj105 d1: central semiconductor cmdsh2-3 l1: murata lqh32cn-220 or equivalent v out 12v 40ma load current (ma) 010 20 30 40 efficiency (%) 3460 ta03a 85 80 75 70 65 60 55
lt3460/lt3460-1 9 3460fb typical applications 5v to 12v step-up converter ef? ciency v in 2.7v to 4.2v l1 10h d1 39.2k 13k c2 4.7f 6.3v 50pf c1 4.7f v in sw fb shdn gnd lt3460 3460 ta07 c1: taiyo yuden x5r jmk212bj475 c2: taiyo yuden x5r jmk212bj475 d1: philips pmeg2010 l1: murata lqh32cn-100 or equivalent v out 5v + load current (ma) 0 80 82 84 150 3460 ta07a 78 76 74 50 100 200 250 72 70 efficiency (%) 90 88 86 v in = 2.7v v in = 3v v in = 3.6v v in = 4.2v 12v to 36v step-up converter load step response 5v to 36v step-up converter load step response v in 12v l1 47h d1 d2 278k 10k c2 0.22f 50v 22pf c1 1f 16v v in sw fb shdn gnd lt3460 3460 ta04 c1: taiyo yuden x5r emk212bj105 c2: taiyo yuden x7r umk212bj224 d1, d2: central semiconductor cmod4448 l1: taiyo yuden lb2012 v out 36v 4ma 100s/div 3460 ta04a 4ma 2ma v out 100mv/div i load v in 5v v out 36v 4ma l1 47h d1 d2 278k 10k c2 0.22f 50v 22pf c1 1f 6.3v v in sw fb shdn gnd lt3460 3460 ta05 c1: taiyo yuden x5r jmk107bj105 c2: taiyo yuden x7r umk212bj224 d1, d2: central semiconductor cmod4448 l1: taiyo yuden lb2012 100s/div 3460 ta05a 4ma 2ma v out 100mv/div i load
lt3460/lt3460-1 10 3460fb applications information li-ion to 18v step-up converter v in 2.7v to 4.2v v out 18v 200a l1 d1 1.6m 124k c2 1f 35v c1 1f 6.3v v in sw fb shdn gnd lt3460-1 3460 ta08 c1: taiyo yuden x5r jmk107bj105 c2: taiyo yuden x5r gmk107bj105 d1, d2: central semiconductor cmdsh-3 l1: murata lqh31cn-220 s5 package 5-lead plastic tsot-23 (reference ltc dwg # 05-08-1635) 1.50 C 1.75 (note 4) 2.80 bsc 0.30 C 0.45 typ 5 plcs (note 3) datum a 0.09 C 0.20 (note 3) s5 tsot-23 0302 pin one 2.90 bsc (note 4) 0.95 bsc 1.90 bsc 0.80 C 0.90 1.00 max 0.01 C 0.10 0.20 bsc 0.30 C 0.50 ref 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 package description
lt3460/lt3460-1 11 3460fb 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 representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description sc6 package 6-lead plastic sc70 (reference ltc dwg # 05-08-1638) 1.15 C 1.35 (note 4) 1.80 C 2.40 0.15 C 0.30 6 plcs (note 3) 0.10 C 0.18 (note 3) sc6 sc70 0802 1.80 C 2.20 (note 4) 0.65 bsc pin 1 0.80 C 1.00 1.00 max 0.00 C 0.10 ref 0.10 C 0.40 0.10 C 0.30 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. details of the pin 1 indentifier are optional, but must be located within the index area 7. eiaj package reference is eiaj sc-70 3.26 max 0.47 max 0.65 ref recommended solder pad layout per ipc calculator 0.96 min 2.1 ref 1.16 ref index area (note 6) 2.00 0.10 (4 sides) note: 1. drawing to be made a jedec package outline m0-229 variation of (wccd-2) 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.38 0.05 bottom view?exposed pad 0.56 0.05 (2 sides) 0.75 0.05 r = 0.115 typ 1.37 0.05 (2 sides) 1 3 6 4 pin 1 bar top mark (see note 6) 0.200 ref 0.00 ? 0.05 (dc6) dfn 1103 0.25 0.05 1.42 0.05 (2 sides) recommended solder pad pitch and dimensions 0.61 0.05 (2 sides) 1.15 0.05 0.675 0.05 2.50 0.05 package outline 0.25 0.05 0.50 bsc 0.50 bsc pin 1 chamfer of exposed pad dc package 6-lead plastic dfn (2mm 2mm) (reference ltc dwg # 05-08-1703)
lt3460/lt3460-1 12 3460fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2007 lt 0208 rev b ? printed in usa related parts typical applications part number description comments lt1613 550ma (i sw ), 1.4mhz, high ef? ciency step-up dc/dc converter v in : 0.9v to 10v, v out(max) = 34v, i q = 3ma, i sd <1a, thinsot package lt1615/lt1615-1 300ma/80ma (i sw ), constant off-time, high ef? ciency step- up dc/dc converter v in : 1.2v to 15v, v out(max) = 34v, i q = 20a, i sd <1a, thinsot package lt1944/lt1944-1 dual output 350ma/100ma (i sw ), constant off-time, high ef? ciency step-up dc/dc converter v in : 1.2v to 15v, v out(max) = 34v, i q = 20a, i sd <1a, ms package lt1945 dual output, pos/neg, 350ma (i sw ), constant off-time, high ef? ciency step-up dc/dc converter v in : 1.2v to 15v, v out(max) = 34v, i q = 20a, i sd <1a, ms package lt1961 1.5a (i sw ), 1.25mhz, high ef? ciency step-up dc/dc converter v in : 3v to 25v, v out(max) = 35v, i q = 0.9ma, i sd <6a, ms8e package ltc3400/ltc3400b 600ma (i sw ), 1.2mhz, synchronous step-up dc/dc converter v in : 0.85v to 5v, v out(max) = 5v, i q = 19a/300a, i sd <1a, thinsot package ltc3401/ltc3402 1a/2a (i sw ), 3mhz, synchronous step-up dc/dc converter v in : 0.5v to 5v, v out(max) = 6v, i q = 38a, i sd <1a, ms package lt3461/lt3461a 0.3a (i sw ), 1.3mhz/3mhz, high ef? ciency step-up dc/dc converter with integrated schottky v in : 2.5v to 16v, v out(max) = 38v, i q = 2.8ma, i sd <1a, sc70, thinsot packages lt3464 0.08a (i sw ), high ef? ciency step-up dc/dc converter with integrated schottky, output disconnect v in : 2.3v to 10v, v out(max) = 34v, i q = 25a, i sd <1a, thinsot package lt3465/lt3465a constant current, 1.2mhz/2.7mhz, high ef? ciency white led boost regulator with integrated schottky diode v in : 2.7v to 16v, v out(max) = 30v, i q = 1.9ma, i sd <1a, thinsot package 5v to 5v sepic ef? ciency l1 22h d1 l2 22 h 30k 10k c2 1f 50pf c3 0.22f c1 1f v in sw fb shdn gnd lt3460 3460 ta06 c1, c2: taiyo yuden x5r lmk107bj105 c3: taiyo yuden x7r lmk107bj224 d1: on semiconductor mbr0520 l1, l2: murata lqh32cn-220 or equivalent v in 3v to 10v v out 5v 50ma load current (ma) 050 100 150 efficiency (%) 3460 ta06a 80 75 70 65 60 55 50 v in = 4v v in = 5v v in = 6.5v

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