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1 lt1303/lt1303-5 micropower high efficiency dc/dc converters with low-battery detector adjustable and fixed 5v features n 5v at 200ma from a 2v input n supply voltage as low as 1.8v n up to 88% efficiency n 120 m a quiescent current n low-battery detector n low v cesat switch: 170mv at 1a typ n uses inexpensive surface mount inductors n 8-lead pdip or so package descriptio n u n el panel drivers n 2-cell and 3-cell to 5v conversion n palmtop computers n portable instruments n bar-code scanners n pdas n wireless systems applicatio n s u typical applicatio n u the lt ? 1303/lt1303-5 are micropower step-up high efficiency dc/dc converters using burst mode tm opera- tion. they are ideal for use in small, low-voltage battery- operated systems. the lt1303-5 accepts an input voltage between 1.8v and 5v and converts it to a regulated 5v. the lt1303 is an adjustable version that can supply an output voltage up to 25v. quiescent current is only 120 m a from the battery and the shutdown pin further reduces current to 10 m a. the low-battery detector provides an open- collector output that goes low when the input voltage drops below a preset level. the on-chip npn power switch has a low 170mv saturation voltage at a switch current of 1a. the lt1303/lt1303-5 are available in 8-lead pdip or so packages, easing board space requirements. for higher output current, please see the lt1305 or lt1302. load current (ma) 0.1 30 efficiency (%) 70 80 90 1 100 10 1000 lt1303 ta01 60 50 40 v in = 2v v in = 4v v in = 2.5v v in = 3v 5v output efficiency v in sw gnd pgnd sense lbi lbo shdn lt1303-5 + + 100k 100 m f shutdown 412k 1% 100 m f 2 cells 316k 1% l1 22 m h 1n5817 v out , 5v 200ma low battery goes low at v bat = 2.2v l1 = sumdia cd54-220 lt1303 ta02 figure 1. 2-cell to 5v dc/dc converter with low-battery detect , ltc and lt are registered trademarks of linear technology corporation. burst mode is a trademark of linear technology corporation.
2 lt1303/lt1303-5 symbol parameter conditions min typ max units i q quiescent current v shdn = 0.5v, v sel = 5v, v sense = 5.5v l 120 200 m a v shdn = 1.8v l 715 m a v in input voltage range 1.8 1.55 v l 2.0 v feedback voltage lt1303 l 1.22 1.24 1.26 v output sense voltage lt1303-5 l 4.8 5.0 5.2 v comparator hysteresis lt1303 (note 1) l 6 12.5 mv output hysteresis lt1303-5 (note 1) l 22 50 mv feedback pin bias current lt1303, v fb = 1v l 720 na oscillator frequency current limit not asserted 120 155 185 khz oscillator tc 0.2 %/ c dc maximum duty cycle l 75 86 95 % t on switch on time current limit not asserted 5.6 m s output line regulation 1.8v < v in < 6v l 0.06 0.15 %/v v cesat switch saturation voltage i sw = 700ma l 130 200 mv switch leakage current v sw = 5v, switch off l 0.1 10 m a peak switch current v in = 2v l 0.75 1.0 1.25 a v in = 5v 0.65 0.9 1.15 a lbi trip voltage l 1.21 1.24 1.27 v lbi input bias current v lbi = 1v l 720 na lbo output low i load = 100 m a l 0.11 0.4 v lbo leakage current v lbi = 1.3v, v lbo = 5v l 0.1 5 m a v shdnh shutdown pin high l 1.8 v v shdnl shutdown pin low 0.5 v i shdn shutdown pin bias current v shdn = 5v l 8.0 20 m a v shdn = 2v l 3.0 m a v shdn = 0v l 0.1 1 m a absolute m axi m u m ratings w ww u v in voltage .............................................................. 10v sw1 voltage ............................................................ 25v sense voltage (lt1303-5) ....................................... 20v fb voltage (lt1303) ................................................ 10v shutdown voltage ................................................... 10v lbo voltage ............................................................. 10v lbi voltage .............................................................. 10v maximum power dissipation ............................. 500mw operating temperature range ..................... 0 c to 70 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c package/order i n for m atio n w u u t a = 25 c, v in = 2.0v, unless otherwise noted. e lectr ic al c c hara terist ics note 1: hysteresis specified is dc. output ripple may be higher if output capacitance is insufficient or capacitor esr is excessive. the l denotes specifications which apply over the 0 c to 70 c operating temperature range. order part number lt1303cn8 lt1303cs8 lt1303cn8-5 lt1303cs8-5 s8 part marking 1303 13035 consult factory for industrial and military grade parts. 1 2 3 4 8 7 6 5 top view gnd lbo shdn fb (sense)* pgnd sw v in lbi n8 package 8-lead pdip s8 package 8-lead plastic so *fixed version t jmax = 100 c, q ja = 130 c/w (n8) t jmax = 100 c, q ja = 150 c/w (s8)
3 lt1303/lt1303-5 typical perfor m a n ce characteristics u w switch current (a) 0.1 v cesat (mv) 150 200 250 225 175 125 75 25 0.8 lt1303 g01 100 50 0 0.2 1.0 0.3 0.5 0.7 0.9 0.4 0.6 1.0 lt1303 fb voltage temperature ( c) ?0 100 v cesat (mv) 120 130 140 150 160 170 ?5 0 25 50 lt1303 g02 75 180 190 200 110 100 i sw = 700ma lt1303-5 sense pin resistance to ground low battery detect trip point lt1303-5 sense voltage temperature (?c) ?0 700 800 900 25 75 lt1303 go3 600 500 ?5 0 50 100 400 300 resistance (k w ) 1000 v cesat vs switch current lbi pin bias current fb pin bias current switch current limit temperature ( c) ?0 1.200 feedback voltage (v) 1.210 1.215 1.220 1.225 1.230 1.235 ?5 0 25 50 lt1330 g04 75 1.240 1.245 1.250 1.205 100 temperature ( c) ?0 1.200 lbi voltage (v) 1.210 1.215 1.220 1.225 1.230 1.235 ?5 0 25 50 lt1303 g06 75 1.240 1.245 1.250 1.205 100 temperature ( c) ?0 4.90 sense voltage (v) 4.94 4.96 4.98 5.00 5.02 5.04 ?5 0 25 50 lt1303 g05 75 5.06 5.08 5.10 4.92 100 temperature ( c) ?0 0 bias current (na) 4 6 8 10 12 14 ?5 0 25 50 lt1303 g07 75 16 18 20 2 100 temperature ( c) ?0 ?5 25 75 0.60 switch current (a) 0.70 0.90 1.00 1.10 50 1.50 lt1303 g09 0.80 0 100 1.20 1.30 1.40 v in = 2v temperature ( c) ?0 0 bias current (na) 4 6 8 10 12 14 ?5 0 25 50 lt1303 g08 75 16 18 20 2 100 v cesat vs temperature
4 lt1303/lt1303-5 typical perfor m a n ce characteristics u w oscillator frequency switch on-time maximum duty cycle temperature ( c) ?0 2 on-time ( m s) 3 4 5 6 8 ?5 02550 lt1303 g10 75 100 7 temperature ( c) ?0 100 frequency (khz) 120 130 140 150 160 170 ?5 0 25 50 lt1303 g11 75 180 190 200 110 100 temperature ( c) ?0 50 duty cycle (%) 60 65 70 75 80 85 ?5 0 25 50 lt1303 g12 75 90 95 100 55 100 quiescent current quiescent current switch current limit temperature ( c) ?0 100 quiescent current ( m a) 120 130 140 150 160 170 ?5 0 25 50 lt1303 g13 75 180 190 200 110 100 switch off v in = 2v input voltage (v) 0 switch current (ma) 1000 1100 1200 8 lt1303 g15 900 800 700 2 4 6 10 l = 33 m h v l = 3v input voltage (v) 0 quiescent current ( m a) 300 400 500 8 lt1303 g14 200 100 0 2 4 6 10 t a = 25 c switch off 200 m s/div transient response figure 1 circuit v in = 2v v out = 5v lt1303 g16 200ma 0ma v out 100mv/div ac coupled i load r pull-up = 47k low battery detector transient response lt1303 g18 5 m s/div v lbo 2v/div v trip +10mv v trip C10mv lt1303 g17 500 m s/div 5v shutdown pin response r load = 100 w v in = 2v v out = 5v c out = 100 m f v out 1v/div v shdn 5v/div v lbi
5 lt1303/lt1303-5 pi n fu n ctio n s uuu gnd (pin 1): signal ground. tie to pgnd under the package. lbo (pin 2): open-collector output of low-battery com- parator. can sink 100 m a. disabled when device is in shutdown. shdn (pin 3): shutdown. pull high to shut down the device. ground for normal operation. fb/sense (pin 4): on 1303 (adjustable) this pin connects to the main comparator c1 input. on lt1303-5 this pin connects to the resistor string that sets output voltage at 5v. lbi (pin 5): low-battery comparator input. when voltage on this pin below 1.24v, lbo is low. v in (pin 6): supply pin. must be bypassed with a large value electrolytic to ground. keep bypass within 0.2" of the device. sw (pin 7): switch pin. connect inductor and diode here. keep layout short and direct to minimize radio frequency interference. pgnd (pin 8): power ground. tie to signal ground (pin1) under the package. bypass capacitor from v in should be tied directly to pgnd within 0.2" of the device. w i dagra b l o c k s figure 2. lt1303 block digram + + + 6 7 8 3 2 5 1 4 + + c1 c2 l1 d1 v in v in r1 3 w q2 1 q1 160 shutdown lbo lbi gnd pgnd sw r1 r2 c3 c2 c1 fb off oscillator a3 driver current comparator hysteretic comparator reference 1.24v 18mv lt1303 bd01
6 lt1303/lt1303-5 w i dagra b l o c k s if switch current reaches 1a, causing c2 to trip, switch on- time is reduced and off-time increases slightly. this allows continuous operation during bursts. c2 monitors the voltage across 3 w resistor r1 which is directly related to the switch current. q2s collector current is set by the emitter-area ratio to 0.6% of q1s collector current. when r1s voltage drop exceeds 18mv, corresponding to 1a switch current, c2s output goes high, truncating the on- time portion of the oscillator cycle and increasing off-time operatio n u operation of the lt1303 is best understood by referring to the block diagram in figure 2. when c1s negative input, related to the output voltage by the appropriate resistor- divider ratio, is higher than the 1.24v reference voltage, c1s output is low. c2, a3 and the oscillator are turned off, drawing no current. only the reference and c1 consume current, typically 140 m a. when c1s negative input drops below 1.24v and overcomes c1s 6mv hysteresis, c1s output goes high, enabling the oscillator, current compara- tor c2 and driver a3. quiescent current increases to 2ma as the device goes into active switching mode. q1 then turns on in controlled saturation for nominally 6 m s or until current comparator c2 trips, whichever comes first. the switch then turns off for approximately 1.5 m s, then turns on again. the lt1303s switching causes current to alter- nately build up in l1 and dump into output capacitor c4 via d1, increasing the output voltage. when the output is high enough to cause c1s output to go high, switching action ceases. capacitor c4 is left to supply current to the load until v out decreases enough to force c1s output high, and the entire cycle repeats. figure 4 details relevant wave- forms. c1s cycling causes low-to-mid-frequency ripple voltage on the output. ripple can be reduced by making the output capacitor large. the 100 m f unit specified results in ripple of 50mv to 100mv on the 5v output. a 220 m f capacitor will decrease ripple by approximately 50%. + + + 6 7 8 3 2 5 1 4 v in r1 3 w q2 1 q1 160 shutdown lbo lbi gnd pgnd r1 474k r2 156k c3 c2 c1 fb sw off oscillator a3 driver current comparator hysteretic comparator reference 1.24v 18mv lt1303 bd02 figure 3. lt1303-5 block diagram 20 m s/div v out 100mv/div ac coupled lt1303 f04 figure 4. burst mode operation in action i l 1a/div v sw 5v/div
7 lt1303/lt1303-5 inductor section inductors suitable for use with the lt1303 usually fall in the 5 m h to 50 m h range. the inductor must: (1) handle current of 1.25a without saturating, (2) have enough inductance to provide a di/dt lower than 400ma/ m s, and (3) have low enough dc resistance to avoid excessive heating or efficiency losses. higher value inductors will deliver more power but tend to be physically larger. most ferrite core drum or rod inductors such as those specified in table 1 are suitable for use. it is acceptable to bias open- flux inductors (e.g. sumida cd54) into saturation by 10 to 20% without adverse effects. operatio n u applicatio n s i n for m atio n wu u u hysteresis built in, but hysteresis can be added by connecting a high-value resistor from lbi to lbo as shown in figure 5. the internal reference can be accessed via the comparator as shown in figure 6. figure 7 shows inductor current of a suitable inductor, di/dt is controlled at all times. the rapid rise in current shown in figure 8 results from this inductor saturating at approximately 1a. saturation occurs when the inductor cannot hold any more magnetic energy in the core. current then increases rapidly, limited only by the resistance of the winding. figure 9s inductor has high dc resistance which results in the exponential time constant shape of the inductor current. figure 7. properly chosen inductor does not saturate i l 500ma/div 5 m s/div lt1303 f07 figure 6. accessing internal reference to about 2 m s. response time of c2, which determines minimum on-time, is approximately 300ns. low battery detector the low battery detector is enabled when shdn is low and disabled when shdn is high. the comparator has no figure 5. r3 adds hysteresis to low-battery detector + 1.24v lt1303 r4 47k r1 r3 2m r2 49.9k 1% v bat 5v r1 = (v trip ?.24v) (43.5k) hysteresis ? 30mv lt1303 f05 phone vendor series appropriate values numbers coilcraft d03316 10 m h to 47 m h (708) 639-6400 d01608 10 m h coiltronics octapak (407) 241-7876 ctx20-1 20 m h ctx20-2 20 m h ctx33-4 33 m h sumida cd54 10 m h to 33 m h (708) 956-0666 gowanda ga10 10 m h to 33 m h (716) 532-2234 table 1. recommended inductors v in v in gnd lbo lbi lt1303 + 100k r2 r1 2.2 m f 2n3906 v ref output v ref = 1.24v 1 + v in 3 v ref + 200mv r1 + r2 ? 33k r2 r1 () lt1303 f06
8 lt1303/lt1303-5 applicatio n s i n for m atio n wu u u figure 8. this inductor saturates at i l ? 1a. a poor choice lt1303 f08 phone vendor series type numbers avx tps surface mount (803) 448-9411 sanyo os-con through-hole (619) 661-6835 panasonic hfq through-hole (201) 348-5200 sprague 595d surface mount (603) 224-1961 table 2. recommended capacitors capacitor selection input and output capacitors should have low esr for best efficiency. recommended capacitors include avx tps series, sprague 595d series, and sanyo os-con. the output capacitors esr determines the high frequency ripple amplitude. a 100 m f capacitor is the minimum rec- ommended for a 5v output. higher output voltages can use lower capacitance values. for example, a 12v output can use a 33 m f or 47 m f capacitor. the v in pin of the lt1303 should be decoupled with a 47 m f or 100 m f capacitor at the pin. when driving a transformer, an additional decoupling network of 10 w and 0.1 m f ceramic is recommended as shown in figure 10. diode selection the lt1303s high switching speed demands a high speed rectifier. schottky diodes are preferred for their low for- ward drop and fast recovery. suitable choices include the 1n5817, mbrs120lt3, and mbr0520lt1. do not use signal diodes such as 1n4148. they cannot carry 1a current. also avoid general-purpose diodes such as 1n4001. these are far too slow and are unsuitable for any switching regulator application. for high temperature applications a silicon diode such as the mur105 will have less leakage. lt1303 f09 figure 9. slight exponential shape to inductor current waveform indicates excessive dc resistance + 47 m f 0.1 m f ceramic 10 w v in ? ? lt1303 f10 v in sw gnd pgnd lt1303 figure 10. 10 w -1 m f network to lt1303 v in pin provides additional decoupling. recommended when driving transformers.
9 lt1303/lt1303-5 typical applicatio n s u setting output voltage on lt1303 5v step-up converter with reference output v in r2 100 m f 1n5817 1303 ta03 l1 r1 + 100 m f v out + v out = 1.24v 1 + () r2 r1 v in sw fb pgnd gnd lt1303 33k input 1.8v to 4.5v v ref output 1.24v 100 m f 1n5817 1303 ta04 22 m h* 100k + 2.2 m f + 100 m f output 5v + 2n3906 * sumida cd54-220mc v in sw gnd pgnd sense shdn lbi lt1303-5 lbo
10 lt1303/lt1303-5 typical applicatio n s u 4-, 5-cell to 5v converter with output disconnect v in sw gnd pgnd sense shdn lt1303-5 + + + 10 m h* 33 m f 33 m f shutdown 220 m f** v in 2v to 8v 510 w mbrs130t3 ztx788b v out 5v 100ma sumida cd54-100mc avx tps 220 m f/10v * ** lt1303ta05 3-cell to 3.3v boost/linear converter with output disconnect v in sw gnd pgnd shdn lbi lb0 fb lt1303 + + shutdown 10 m h* 33 m f 33 m f 1.96k ? 100k 100 w 200k ? 121k ? 330 m f** 2 mbrs130t3 si9433 sumida cd54-100mc avx tps 330 m f/6.3v 1% metal film * ** ? v in 2v to 6v v out 3.3v/200ma lt1303 ta07 +
11 lt1303/lt1303-5 typical applicatio n s 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 circuits as described herein will not infringe on existing patent rights. el panel driver v in sw gnd pgnd shdn fb lt1303 + + 47 m f 0.1 m f ceramic 10 w v in 1.5v to 8v lt1303 ta06 shutdown 1n5818 1n4148 3.3m 3.3m 3.3m 51k r1 ? 25k 10k 1k 1/2w mpsa42 4.7 m f 160v c1* 50pf mur160 el panel t1** 1:15 4,5 1,2 6 10 100hz to 1000hz square wave drive add c1 for open-panel protection dale lpe5047-a132 1:15 turns ratio (605) 666-9301 r1 adjusts v out 83v rms to 115v rms * ** ?
12 lt1303/lt1303-5 lt/gp 0195 10k ? printed in usa ? linear technology corporation 1995 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7487 (408) 432-1900 l fax : (408) 434-0507 l telex : 499-3977 package descriptio n u dimensions in inches (millimeters) unless otherwise noted. n8 package 8-lead plastic dip n8 0695 0.005 (0.127) min 0.100 0.010 (2.540 0.254) 0.065 (1.651) typ 0.045 ?0.065 (1.143 ?1.651) 0.130 0.005 (3.302 0.127) 0.015 (0.380) min 0.018 0.003 (0.457 0.076) 0.125 (3.175) min 0.009 ?0.015 (0.229 ?0.381) 0.300 ?0.325 (7.620 ?8.255) 0.325 +0.025 0.015 +0.635 0.381 8.255 () 12 3 4 87 6 5 0.255 0.015* (6.477 0.381) 0.400* (10.160) max *these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed 0.010 inch (0.254mm) related parts part number description comments lt1129 micropower low dropout regulator 700ma output current in so-8 package lt1182/83/84 lcd and ccfl backlight controller high efficiency and excellent backlight control range lt1301 5v to 12v/200ma step-up dc/dc converter 120 m a quiescent current lt1302 2-cell to 5v/600ma step-up dc/dc converter 200 m a quiescent current lt1305 micropower 2a switch dc/dc converter with low-battery detect 2v to 5v at 400ma lt1372 500khz step-up pwm, 1.5a switch low noise, fixed frequency operation ltc ? 1472 pcmcia host switch with protection includes current limit and thermal shutdown s8 package 8-lead plastic soic 0.016 ?0.050 0.406 ?1.270 0.010 ?0.020 (0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010 (0.203 ?0.254) so8 0695 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) bsc 1 2 3 4 0.150 ?0.157** (3.810 ?3.988) 8 7 6 5 0.189 ?0.197* (4.801 ?5.004) 0.228 ?0.244 (5.791 ?6.197) dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * **

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