1 lt1615/LT1615-1 sn16151 16151fas micropower step-up dc/dc converters in thinsot the lt ? 1615/LT1615-1 are micropower step-up dc/dc converters in a 5-lead low profile (1mm) thinsot pack- age. the lt1615 is designed for higher power systems with a 350ma current limit and an input voltage range of 1.2v to 15v, whereas the LT1615-1 is intended for lower power and single-cell applications with a 100ma current limit and an extended input voltage range of 1v to 15v. otherwise, the two devices are functionally equivalent. both devices feature a quiescent current of only 20 m a at no load, which further reduces to 0.5 m a in shutdown. a current limited, fixed off-time control scheme conserves operating current, resulting in high efficiency over a broad range of load current. the 36v switch allows high voltage outputs up to 34v to be easily generated in a simple boost topology without the use of costly transformers. the lt1615s low off-time of 400ns permits the use of tiny, low profile inductors and capacitors to minimize footprint and cost in space-conscious portable applications. n low quiescent current: 20 m a in active mode <1 m a in shutdown mode n operates with v in as low as 1v n low v cesat switch: 250mv at 300ma n uses small surface mount components n high output voltage: up to 34v n low profile (1mm) thinsot tm package n lcd bias n handheld computers n battery backup n digital cameras , ltc and lt are registered trademarks of linear technology corporation. 1-cell li-ion to 20v converter for lcd bias v in sw fb lt1615 v in 2.5v to 4.2v l1 10 h d1 shdn r2 130k r1 2m c2 1 f 20v 12ma c1: taiyo yuden lmk316bj475 c2: taiyo yuden tmk316bj105 d1: motorola mbr0530 l1: murata lqh3c100k24 1615/-1 ta01 gnd c1 4.7 f efficiency load current (ma) 0.1 0.3 efficiency (%) 1 3 10 30 1615 /-1 ta01a 85 80 75 70 65 60 55 50 v in = 4.2v v in = 2.5v v in = 3.3v applicatio s u features typical applicatio u descriptio u thinsot is a trademark of linear technology corporation.
2 lt1615/LT1615-1 sn16151 16151fas absolute axi u rati gs w ww u package/order i for atio uu w (note 1) v in , shdn voltage ................................................... 15v sw voltage .............................................................. 36v fb voltage .................................................................v in current into fb pin ................................................. 1ma junction temperature ........................................... 125 c operating temperature range (note 2) .. C 40 c to 85 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c order part number lt1615es5 lt1615es5-1 lt1615is5 lt1615is5-1 s5 part marking sw 1 gnd 2 top view s5 package 5-lead plastic sot-23 fb 3 5 v in 4 shdn electrical characteristics the l denotes the specifications which apply over the full operating parameter conditions min typ max units minimum input voltage LT1615-1 1.0 v lt1615 1.2 v quiescent current not switching 20 30 m a v shdn = 0v 1 m a fb comparator trip point l 1.205 1.23 1.255 v fb comparator hysteresis 8mv output voltage line regulation 1.2v < v in < 12v 0.05 0.1 %/v fb pin bias current (note 3) v fb = 1.23v l 30 80 na switch off time v fb > 1v 400 ns v fb < 0.6v 1.5 m s switch v cesat i sw = 70ma (LT1615-1) 85 120 mv i sw = 300ma (lt1615) 250 350 mv switch current limit LT1615-1 75 100 125 ma lt1615 300 350 400 ma shdn pin current v shdn = 1.2v 2 3 m a v shdn = 5v 8 12 m a shdn input voltage high 0.9 v shdn input voltage low 0.25 v switch leakage current switch off, v sw = 5v 0.01 5 m a note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: the lt1615e and lt1615e-1 are 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, t jmax = 125 c, q ja = 256 c/w temperature range, otherwise specifications are at t a = 25 c. v in = 1.2v, v shdn = 1.2v unless otherwise noted. ltiz ltkh ltxz ltbht characterization and correlation with statistical process controls. the lt1615i/lt1615i-1 is guaranteed to meet performance specifications over the C40 c to 85 c operating temperature range. note 3: bias current flows into the fb pin. consult ltc marketing for parts specified with wider operating temperature ranges.
3 lt1615/LT1615-1 sn16151 16151fas typical perfor a ce characteristics uw switch saturation voltage (v cesat ) quiescent current feedback pin voltage and bias current temperature ( c) ?0 ?5 0 25 50 75 100 switch voltage (v) 1615/-1 g01 0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 i switch = 500ma i switch = 300ma temperature ( c) ?0 feedback voltage (v) 1615/-1 g02 1.25 1.24 1.23 1.22 1.21 1.20 bias current (na) 50 40 30 20 10 0 current voltage 25 0 25 50 75 100 temperature ( c) quiescent current ( a) 1615/-1 g03 25 23 21 19 17 15 ?0 ?5 0 25 50 75 100 v in = 12v v in = 1.2v v fb = 1.23v not switching pi fu ctio s uuu sw (pin 1): switch pin. this is the collector of the internal npn power switch. minimize the metal trace area con- nected to this pin to minimize emi. gnd (pin 2): ground. tie this pin directly to the local ground plane. fb (pin 3): feedback pin. set the output voltage by selecting values for r1 and r2 (see figure 1): rr v out 12 123 1 =- ? ? ? ? . shdn (pin 4): shutdown pin. tie this pin to 0.9v or higher to enable the device. tie below 0.25v to turn off the device. v in (pin 5): input supply pin. bypass this pin with a capacitor as close to the device as possible. temperature ( c) switch off time (ns) 1615/-1 g04 550 500 450 400 350 300 250 ?0 ?5 0 25 50 75 100 v in = 1.2v v in = 12v temperature ( c) peak current (ma) 1615/-1 g05 400 350 300 250 200 150 100 50 0 ?0 ?5 0 25 50 75 100 v in = 12v v in = 1.2v v in = 12v LT1615-1 lt1615 v in = 1.2v shutdown pin voltage (v) shutdown pin current ( a) 1615/-1 g03 25 20 15 10 5 0 0 5 10 15 25 c 100 c switch off time shutdown pin current switch current limit
4 lt1615/LT1615-1 sn16151 16151fas block diagra w figure 1. lt1615 block diagram + + 5 400ns one-shot driver reset enable 42mv* 0.12 a2 a1 q3 2 r4 140k r3 30k r6 40k r5 40k q2 x10 q1 3 v in fb 4 shdn 1 sw gnd 1615/-1 bd l1 c2 v out v in d1 r2 (external) r1 (external) v out c1 * 12mv for LT1615-1 operatio u the lt1615 uses a constant off-time control scheme to provide high efficiencies over a wide range of output current. operation can be best understood by referring to the block diagram in figure 1. q1 and q2 along with r3 and r4 form a bandgap reference used to regulate the output voltage. when the voltage at the fb pin is slightly above 1.23v, comparator a1 disables most of the internal cir- cuitry. output current is then provided by capacitor c2, which slowly discharges until the voltage at the fb pin drops below the lower hysteresis point of a1 (typical hysteresis at the fb pin is 8mv). a1 then enables the internal circuitry, turns on power switch q3, and the current in inductor l1 begins ramping up. once the switch current reaches 350ma, comparator a2 resets the one- shot, which turns off q3 for 400ns. l1 then delivers current to the output through diode d1 as the inductor current ramps down. q3 turns on again and the inductor current ramps back up to 350ma, then a2 resets the one- shot, again allowing l1 to deliver current to the output. this switching action continues until the output voltage is charged up (until the fb pin reaches 1.23v), then a1 turns off the internal circuitry and the cycle repeats. the lt1615 contains additional circuitry to provide protection during start-up and under short-circuit conditions. when the fb pin voltage is less than approximately 600mv, the switch off-time is increased to 1.5 m s and the current limit is reduced to around 250ma (70% of its normal value). this reduces the average inductor current and helps minimize the power dissipation in the lt1615 power switch and in the external inductor and diode. the LT1615-1 operates in the same manner, except the switch current is limited to 100ma (the a2 reference voltage is 12mv instead of 42mv).
5 lt1615/LT1615-1 sn16151 16151fas choosing an inductor several recommended inductors that work well with the lt1615 and LT1615-1 are listed in table 1, although there are many other manufacturers and devices that can be used. consult each manufacturer for more detailed infor- mation and for their entire selection of related parts. many different sizes and shapes are available. use the equations and recommendations in the next few sections to find the correct inductance value for your design. table 1. recommended inductors part value ( m h) max dcr ( w ) vendor lqh3c4r7 4.7 0.26 murata lqh3c100 10 0.30 (814) 237-1431 lqh3c220 22 0.92 www.murata.com cd43-4r7 4.7 0.11 sumida cd43-100 10 0.18 (847) 956-0666 cdrh4d18-4r7 4.7 0.16 www.sumida.com cdrh4d18-100 10 0.20 do1608-472 4.7 0.09 coilcraft do1608-103 10 0.16 (847) 639-6400 do1608-223 22 0.37 www.coilcraft.com inductor selectionboost regulator the formula below calculates the appropriate inductor value to be used for a boost regulator using the lt1615 or LT1615-1 (or at least provides a good starting point). this value provides a good tradeoff in inductor size and system performance. pick a standard inductor close to this value. a larger value can be used to slightly increase the available output current, but limit it to around twice the value calculated below, as too large of an inductance will in- crease the output voltage ripple without providing much additional output current. a smaller value can be used (especially for systems with output voltages greater than 12v) to give a smaller physical size. inductance can be calculated as: l vv v i t out in min d lim off = -+ () where v d = 0.4v (schottky diode voltage), i lim = 350ma or 100ma, and t off = 400ns; for designs with varying v in such as battery powered applications, use the minimum applicatio s i for atio wu u u v in value in the above equation. for most systems with output voltages below 7v, a 4.7 m h inductor is the best choice, even though the equation above might specify a smaller value. this is due to the inductor current over- shoot that occurs when very small inductor values are used (see current limit overshoot section). for higher output voltages, the formula above will give large inductance values. for a 2v to 20v converter (typical lcd bias application), a 21 m h inductor is called for with the above equation, but a 10 m h inductor could be used without excessive reduction in maximum output current. inductor selectionsepic regulator the formula below calculates the approximate inductor value to be used for a sepic regulator using the lt1615. as for the boost inductor selection, a larger or smaller value can be used. l vv i t out d lim off = + ? ? ? ? 2 current limit overshoot for the constant off-time control scheme of the lt1615, the power switch is turned off only after the 350ma (or 100ma) current limit is reached. there is a 100ns delay between the time when the current limit is reached and when the switch actually turns off. during this delay, the inductor current exceeds the current limit by a small amount. the peak inductor current can be calculated by: ii vv l ns peak lim in max sat =+ - ? ? ? ? () 100 where v sat = 0.25v (switch saturation voltage). the current overshoot will be most evident for systems with high input voltages and for systems where smaller induc- tor values are used. this overshoot can be beneficial as it helps increase the amount of available output current for smaller inductor values. this will be the peak current seen by the inductor (and the diode) during normal operation. for designs using small inductance values (especially at
6 lt1615/LT1615-1 sn16151 16151fas applicatio s i for atio wu u u input voltages greater than 5v), the current limit over- shoot can be quite high. although it is internally current limited to 350ma, the power switch of the lt1615 can handle larger currents without problem, but the overall efficiency will suffer. best results will be obtained when i peak is kept below 700ma for the lt1615 and below 400ma for the LT1615-1. capacitor selection low esr (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. multilayer ceramic capacitors are the best choice, as they have a very low esr and are available in very small packages. their small size makes them a good companion to the lt1615s sot-23 package. solid tantalum capaci- tors (like the avx tps, sprague 593d families) or os-con capacitors can be used, but they will occupy more board area than a ceramic and will have a higher esr. always use a capacitor with a sufficient voltage rating. ceramic capacitors also make a good choice for the input decoupling capacitor, which should be placed as close as possible to the lt1615. a 4.7 m f input capacitor is suffi- cient for most applications. table 2 shows a list of several capacitor manufacturers. consult the manufacturers for more detailed information and for their entire selection of related parts. diode selection for most lt1615 applications, the motorola mbr0520 surface mount schottky diode (0.5a, 20v) is an ideal choice. schottky diodes, with their low forward voltage drop and fast switching speed, are the best match for the lt1615. for higher output voltage applications the 30v mbr0530 can be used. many different manufacturers make equivalent parts, but make sure that the component is rated to handle at least 0.35a. for LT1615-1 applica- tions, a philips bat54 or central semiconductor cmdsh-3 works well. lowering output voltage ripple using low esr capacitors will help minimize the output ripple voltage, but proper selection of the inductor and the output capacitor also plays a big role. the lt1615 pro- vides energy to the load in bursts by ramping up the inductor current, then delivering that current to the load. if too large of an inductor value or too small of a capacitor value is used, the output ripple voltage will increase because the capacitor will be slightly overcharged each burst cycle. to reduce the output ripple, increase the output capacitor value or add a 4.7pf feed-forward capaci- tor in the feedback network of the lt1615 (see the circuits in the typical applications section). adding this small, inexpensive 4.7pf capacitor will greatly reduce the output voltage ripple. table 2. recommended capacitors capacitor type vendor ceramic taiyo yuden (408) 573-4150 www.t-yuden.com ceramic avx (803) 448-9411 www.avxcorp.com ceramic murata (714) 852-2001 www.murata.com
7 lt1615/LT1615-1 sn16151 16151fas typical applicatio s u 2-cell to 3.3v boost converter v in sw fb lt1615 v in 1.5v to 3v l1 4.7 h d1 shdn 604k 1m c2 22 f 3.3v 60ma 1615/-1 ta03 gnd c1 4.7 f c1: taiyo yuden lmk316bj475 (408) 573-4150 c2: taiyo yuden jmk325bj226 (408) 573-4150 l1: murata lqh3c4r7m24 (814) 237-1431 d1: motorola mbr0520 (800) 441-2447 43 2 1 5 4.7pf load current (ma) 0.1 efficiency (%) 90 85 80 75 70 65 60 55 50 1 10 100 1615/-1 ta03a v in = 3v v in = 1.5v 2-cell to 3.3v converter efficiency 1-cell to 3.3v boost converter 4-cell to 5v sepic converter v in sw fb lt1615 v in 3v to 6v l1 10 h d1 c3 1 f shdn 324k 1m c2 10 f 5v 40ma 1615/-1 ta07 gnd c1 4.7 f c1: taiyo yuden lmk316bj475 (408) 573-4150 c2: taiyo yuden jmk316bj106 (408) 573-4150 c3: taiyo yuden jmk107bj105 (408) 573-4150 l1, l2: murata lqh3c100k24 (814) 237-1431 d1: motorola mbr0520 (800) 441-2447 l2 10 h 43 2 1 5 4.7pf 1-cell li-ion to 3.3v sepic converter v in sw fb lt1615 v in 2.5v to 4.2v l1 10 h d1 c3 1 f shdn 604k 1m c2 10 f 3.3v 50ma 1615/-1 ta07 gnd c1 4.7 f c1: taiyo yuden lmk316bj475 (408) 573-4150 c2: taiyo yuden jmk316bj106 (408) 573-4150 c3: taiyo yuden jmk107bj105 (408) 573-4150 l1, l2: murata lqh3c100k24 (814) 237-1431 d1: motorola mbr0520 (800) 441-2447 l2 10 h 43 2 1 5 4.7pf 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. v in sw fb LT1615-1 v in 1v to 1.5v l1 22 h d1 shdn 604k 1m c2 10 f 3.3v 15ma 1615/-1 ta04 gnd c1 4.7 f c1: taiyo yuden lmk316bj475 (408) 573-4150 c2: taiyo yuden jmk316bj106 (408) 573-4150 l1: murata lqh3c220k24 (814) 237-1431 d1: central semiconductor cmdsh-3 (516) 435-1110 43 2 1 5 4.7pf pin diode driver v in sw fb LT1615-1 v in 1v to 6v l1 22 h d1 shdn 365k 10m c2 1 f 35v 500 a 1615/-1 ta09 gnd c1 4.7 f c1: taiyo yuden emk316bj475 (408) 573-4150 c2: taiyo yuden gmk316bj105 (408) 573-4150 l1: murata lqh3c220k24 (814) 237-1431 d1: motorola mbr0540 (800) 441-2447 43 2 1 5
8 lt1615/LT1615-1 sn16151 16151fas linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear-tech.com ? linear technology corporation 1998 16151fa lt/tp 0601 1.5k rev a ? printed in usa related parts part number description comments lt1307 single-cell micropower 600khz pwm dc/dc converter 3.3v at 75ma from one cell, msop package lt1316 burst mode tm operation dc/dc with programmable current limit 1.5v minimum, precise control of peak current limit lt1317 2-cell micropower dc/dc with low-battery detector 3.3v at 200ma from two cells, 600khz fixed frequency lt1610 single-cell micropower dc/dc converter 3v at 30ma from 1v, 1.7mhz fixed frequency lt1611 1.4mhz inverting switching regulator in 5-lead thinsot C 5v at 150ma from 5v input, tiny thinsot package lt1613 1.4mhz switching regulator in 5-lead thinsot 5v at 200ma from 3.3v input, tiny thinsot package lt1617 micropower inverting dc/dc converter in 5-lead thinsot C15v at 12ma from 2.5v input, tiny thinsot package burst mode is a trademark of linear technology corporation package descriptio u typical applicatio s u v in sw fb lt1615 v in 1.5v to 5v l1 10 h d1 d4 shdn 130k 2m c2 1 f 20v 4ma ?0v 4ma 1615/-1 ta05 gnd c3 1 f c1 4.7 f c1: taiyo yuden lmk316bj475 (408) 573-4150 c2, c3, c4: taiyo yuden tmk316bj105 (408) 573-4150 c5: taiyo yuden lmk212bj105 (408) 573-4150 l1: murata lqh3c100k24 (814) 237-1431 d1, d2, d3, d4: motorola mbr0530 (800) 441-2447 43 2 1 5 4.7pf c4 1 f c5 1 f d3 d2 20v dual output converter with output disconnect s5 package 5-lead plastic sot-23 (reference ltc dwg # 05-08-1633) (reference ltc dwg # 05-08-1635) l datum ? .09 ?.20 (.004 ?.008) (note 2) a1 s5 sot-23 0401 1.50 ?1.75 (.059 ?.069) (note 3) 2.60 ?3.00 (.102 ?.118) .25 ?.50 (.010 ?.020) (5plcs, note 2) pin one 2.80 ?3.10 (.110 ?.118) (note 3) .95 (.037) ref a a2 1.90 (.074) ref .20 (.008) millimeters (inches) note: 1. controlling dimension: millimeters 2. dimensions are in 3. drawing not to scale 4. dimensions are inclusive of plating 5. dimensions are exclusive of mold flash and metal burr 6. mold flash shall not exceed .254mm 7. package eiaj reference is: sc-74a (eiaj) for original jedel mo-193 for thin .90 ?1.45 (.035 ?.057) sot-23 (original) .00 ?.15 (.00 ?.006) .90 ?1.30 (.035 ?.051) .35 ?.55 (.014 ?.021) 1.00 max (.039 max) sot-23 (thinsot) a a1 a2 l .01 ?.10 (.0004 ?.004) .80 ?.90 (.031 ?.035) .30 ?.50 ref (.012 ?.019 ref)
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