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1 for more information www.linear.com/lt138a typical a pplica t ion fea t ures a pplica t ions descrip t ion 5a positive adjustable voltage regulator the lt ? 138a series of adjustable regulators provide 5a output current over an output voltage range of 1.2v to 32v. the internal voltage reference is trimmed to less than 1%, enabling a very tight output voltage . in addition to excellent line and load regulation, with full overload protection, the lt138a incorporates new current limit - ing circuitry allowing large transient load currents to be handled for short periods. transient load currents of up to 12 a can be supplied without limiting, eliminating the need for a large output capacitor. the lt138 a is an improved version of the popular lm138 with improved circuit design and advanced process tech - niques to provide superior performance and reliability. the graph below shows the significant improvement in output voltage tolerance achieved by using the lt138a or lt338a. parallel regulators for higher current* n guaranteed 1% initial tolerance n guaranteed 0.3% load regulation n guaranteed 5a output current n 100% thermal limit burn-in n 12a transient output current n high power linear regulator n battery chargers n power driver n constant-current regulator output voltage error lt338a 0.01?? v in v in this circuit will not work with lm version devices current sharing resistors degrade regulation to 1% * ** v out adj lt350a v in 138/338 ta01 121 1% 5v 8a v out adj 0.016** 365 1% output voltage (v) 1 0 output voltage error (%) 3 5 7 10 10 100 138a/338a ta02 1 4 6 9 12 11 8 2 2% resistors 2% resistors 1% resistors 1% resistors lm338 lm338 lt338a lt338a l, lt , lt c , lt m , linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. obsolete: for information purposes only contact linear technology for potential replacement lt138a/lt338a lm138/lm338 138afd
2 for more information www.linear.com/lt138a p recon d i t ioning a bsolu t e maxi m u m r a t ings power dissipation .............................. internally limited input - to - output voltage differential ......................... 35 v o perating junction temperature range lt 138 a / lm 138 ................................. C 5 5 c to 150 c lt 3 38 a/ lm 3 38 ..................................... 0 c to 125 c (note 1) 2 1 v in case is output adj (gnd*) k package 2-lead to-3 metal can bottom view t jmax = 150c, ja = 35c/w, ja = 1c/w (lt138a/lt138) t jmax = 125c, ja = 35c/w, ja = 1c/w (lt338a/lt338) obsolete package v in v out adj 3 2 1 front view p package 3-lead plastic to-3p t jmax = 125c, ja = 45c/w obsolete package p in c on f igura t ion storage temperature range ................. C 65 c to 150 c lead temperature ( soldering , 10 sec ) ................... 30 0 c 100% thermal limit burn-in lt138a/lt339a lm138/lm338 138afd
3 for more information www.linear.com/lt138a e lec t rical c harac t eris t ics symbol parameter conditions min lt 138a ty p max min lm138 ty p max units v ref reference voltage i out = 10ma, t j = 25c 1.238 1.250 1.262 v 3v (v in C v out ) 35v, 10ma i out 5a, p 50w l 1.225 1.250 1.270 1.119 1.24 1.29 v v out v in line regulation 3v (v in C v out ) 35v, (note 3) l 0.005 0.02 0.01 0.04 0.005 0.02 0.01 0.04 %/ v %/v v out v out load regulation 10ma i out 5a, (note 3) v out 5v v out 5v 5 0.1 15 0.3 5 0.1 15 0.3 mv % v out 5v v out 5v l l 20 0.3 30 0.6 20 0.3 30 0.6 mv % thermal regulation 20 ms pulse 0.002 0.01 0.002 0.01 %/w ripple rejection v out = 10v, f = 120hz c adj = 0f c adj = 10f l l 60 60 75 60 60 75 db db i adj adjust pin current l 45 100 45 100 a i adj adjust pin current change 10ma i out 5a, 3v (v in C v out ) 35v l 0.2 5 0.2 5 a minimum load current (v in C v out ) = 35v l 3.5 5 3.5 5 ma i sc current limit (v in C v out ) 10v dc 0.5ms peak l l 5 6 8 12 5 6 8 12 a a ( v in C v out ) = 30v, t j = 25oc 1 2 1 a v out temp t emperature stability l 1 2 1 % v out time long-t erm stability t a = 125oc, 1000 hours 0.3 1 0.3 1 % e n rms output noise (% of v out ) 10hz f 10khz 0.001 0.003 % jc thermal resistance junction-to-case k package 1 1 o c/w the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. (note 2) the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. symbol parameter conditions min lt 138a ty p max min lm138 ty p max units v ref reference voltage i out = 10ma 1.238 1.250 1.262 v 3v (v in C v out ) 35v, 10ma i out 5a, p 50w l 1.225 1.250 1.270 1.19 1.24 1.29 v v out v in line regulation 3v (v in C v out ) 35v, (note 3) l 0.005 0.02 0.01 0.04 0.005 0.02 0.03 0.06 %/ v %/v v out v out load regulation 10ma i out 5a, (note 3) v out 5v v out 5v 5 0.1 15 0.3 5 0.1 25 0.5 mv % v out 5v v out 5v l l 20 0.3 30 0.6 20 0.3 50 1 mv % thermal regulation 20 ms pulse 0.002 0.02 0.002 0.02 %/w lt138a/lt338a lm138/lm338 138afd
4 for more information www.linear.com/lt138a symbol parameter conditions min lt 138a ty p max min lm138 ty p max units ripple rejection v out = 10v, f = 120hz c adj = 0f c adj = 10f l l 60 60 75 60 60 75 db db i adj adjust pin current l 45 100 45 100 a i adj adjust pin current change 10ma i out 5a, 3v (v in C v out ) 35v l 0.2 5 0.2 5 a minimum load current (v in C v out ) = 35v l 3.5 10 3.5 10 ma i sc current limit (v in C v out ) 10v dc 0.5ms peak l l 5 6 8 12 5 6 8 12 a a ( v in C v out ) = 30v, t j = 25oc 1 2 1 a v out temp t emperature stability l 1 2 1 % v out time long-t erm stability t a = 125oc, 1000 hours 0.3 1 0.3 1 % e n rms output noise (% of v out ) 10hz f 10khz 0.001 0.003 % jc thermal resistance junction-to-case k package 1 1 o c/w 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. note 2: unless otherwise specified, these specifications apply: v in C v out = 5v and i out = 2.5a. these specifications are applicable for power dissipations up to 50w. note 3: see thermal regulation specifications for changes in output voltage due to heating effects. load and line regulation are measured at a constant junction temperature by low duty cycle pulse testing. typical p er f or m ance c harac t eris t ics load regulation dropout voltage adjustment current temperature ( c) ?75 ?0.4 output voltage deviation (%) ?0.3 ?0.1 0 0.1 ?25 25 50 150 138/338 g01 ?0.2 ?50 0 75 100 125 0.2 i out = 5a i out = 3a v in = 15v v out = 10v preload = 50ma temperature (c) ?75 1 input-output differential (v) 3 ?25 25 50 150 138/338 g02 2 ?50 0 75 100 125 4 i out = 5a i out = 3a i out = 1a v out = 100mv temperature (c) ?75 adjustment current ( a) 35 40 45 75 65 138a/338a g03 30 ?25 25 125 50 55 60 elec t rical c harac t eris t ics the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. lt138a/lt339a lm138/lm338 138afd
5 for more information www.linear.com/lt138a typical p er f or m ance c harac t eris t ics temperature stability output impedance minimum operating current ripple rejection ripple rejection ripple rejection current limit current limit current limit temperature (c) ?50 1.230 reference voltage (v) 1.240 1.250 1.260 1.270 ?25 0 25 50 138a/338a g04 75 100 125 150 frequency (hz) 10 output impedance ( ) 0.1 1 10 100k 138/338 g05 0.01 0.001 0.0001 100 1k 10k 1m v in = 15v v out = 10v i out = 500ma c adj = c out = 10f c adj = c out = 0f input-output differential (v) 0 quiescent current (ma) 3 4 5 15 25 40 138a/338a g06 2 1 0 5 10 20 30 35 t j = 25c t j = 150c t j = ?55c output voltage (v) 0 5 0 ripple rejection (db) 40 100 10 20 25 138a/338a g07 20 80 60 15 30 35 c adj = 10f c adj = 0f v in ? v out = 5v i out = 500ma f = 120hz t j = 25c frequency (hz) 10 ripple rejection (db) 60 80 100 100k 138a/338a g08 40 20 0 100 1k 10k 1m c adj = 10f c adj = 0f v in = 15v v out = 10v i out = 0.2a output current (a) 0.1 40 ripple rejection (db) 50 60 80 1 10 138/338 g09 70 c adj = 10f c adj = 0f v in = 15v v out = 10v f = 120hz t case = 25c input-output differential (v) 0 output current (a) 8 12 40 138a/338a g10 4 0 10 20 30 16 peak current limit dc current limit t case = 25c preload = 0a preload = 1a preload = 5a time (ms) 0.1 8 output current (a) 10 12 14 1 10 100 138a/338a g11 6 4 2 0 preload = 0a preload = 5a v in = 10v v out = 5v t case = 25c time (ms) 0.1 8 output current (a) 10 12 14 1 10 100 138a/338a g12 6 4 2 0 preload current = 0 t case = 25c v in ? v out = 10v v in ? v out = 15v v in ? v out = 20v v in ? v out = 30v lt138a/lt338a lm138/lm338 138afd
6 for more information www.linear.com/lt138a t ypical per f or m ance charac t eris t ics line transient response load transient response a pplica t ions i n f or m a t ion general the lt138 a develops a 1.25v reference voltage between the output and the adjustable terminal (see figure 1). by placing a resistor , r 1, between these two terminals , a constant current is caused to flow through r1 and down through r2 to set the overall output voltage. normally this current is the specified minimum load current of 5ma or 10ma. because i adj is very small and constant when compared with the current through r 1, it represents a small error and can usually be ignored. it is easily seen from the output voltage equation, that even if the resistors were of exact value, the accuracy of the output is limited by the ac - curacy of v ref . earlier adjustable regulators had a reference tolerance of 4% which is dangerously close to the 5% supply tolerance required in many logic and analog systems. further, even 1% resistors can drift 0.01%/c, adding additional error to the output voltage tolerance. for example , using 2% resistors and 4% tolerance for v ref , calculations will show that the expected range of a 5v regulator design would be 4.66v v out 5.36 v or approximately 7%. if the same example were used for a 15v regulator, the expected tolerance would be 8%. with these results most applications required some method of trimming, usually a trim pot. this solution is both expensive and not conductive to volume production. one of the enhancements of linear technology s adjust - able regulators over existing devices is the tightened initial tolerance of v ref . this allows relatively inexpensive 1% or 2% film resistors to be used for r1 and r2 to set the output voltage within an acceptable tolerance. with a guaranteed 1% reference, a 5v power supply design, using 2% resistors, would have a worst-case manufacturing tolerance of 4%. if 1% resistors are used, the tolerance will drop to 2.5%. a plot of the worst-case output voltage tolerance as a function of resistor tolerance is shown on the front page of this data sheet. for convenience, a table of standard 1% resistor values is shown in table 1. time (s) 0 0 output voltage deviation (v) input voltage change (v) 0.5 ?1.5 ?1.0 ?0.5 20 30 1.5 138a/338a g13 1.0 10 40 0 0.5 1.0 c l = 1f c l = 10f c out = 0 c adj = 0 v out = 10v i out = 50ma t j = 25c time (s) 0 output voltage deviation (v) load current (a) 2 6 ?3 ?2 3 0 20 40 138a/338a g14 4 1 2 ?1 0 10 30 v in = 15v v out = 10v t case = 25c preload = 100ma c l = 1f c adj = 10f c l = 0 c adj = 0 figure 1. basic adjustable regulator lt338a v in r1 138a/338a f01 v out i adj 50a adj v ref v out v in r2 v out = v ref r2 r1 1 + + i adj ? r2 ( ) + lt138a/lt339a lm138/lm338 138afd
7 for more information www.linear.com/lt138a applica t ions in f or m a t ion table 1. 0.5% and 1% standard resistance values 1.00 1.47 2.15 3.16 4.64 6.81 1.02 1.50 2.21 3.24 4.75 6.98 1.05 1.54 2.26 3.32 4.87 7.15 1.07 1.58 2.32 3.40 4.99 7.32 1.10 1.62 2.37 3.48 5.11 7.50 1.13 1.65 2.43 3.57 5.23 7.68 1.15 1.69 2.49 3.65 5.36 7.87 1.18 1.74 2.55 3.74 5.49 8.06 1.21 1.78 2.61 3.83 5.62 8.25 1.24 1.82 2.67 3.92 5.76 8.45 1.27 1.87 2.74 4.02 5.90 8.66 1.30 1.91 2.80 4.12 6.04 8.87 1.33 1.96 2.87 4.22 6.19 9.09 1.37 2.00 2.94 4.32 6.34 9.31 1.40 2.05 3.01 4.42 6.49 9.53 1.43 2.10 3.09 4.53 6.65 9.76 standard resistance values are obtained from the decade table by multiplying by multiples of 10. as an example, 1.21 can represent 1.21, 12.1, 121, 1.21k etc. bypass capacitors input bypassing using a 1f tantalum or 25f electrolytic is recommended when the input filter capacitors are more than 5 inches from the device. improved ripple rejection (80db) can be accomplished by adding a 10f capacitor from the adj pin to ground. increasing the size of the capacitor to 20f will help ripple rejection at low output voltage since the reactance of this capacitor should be small compared to the voltage setting resistor , r2. for improved ac transient response and to prevent the pos - sibility of oscillation due to unknown reactive load, a 1f capacitor is also recommended at the output . because of their low impedance at high frequencies, the best type of capacitor to use is solid tantalum. protection diodes the lt138a/lt338 a do not require a protection diode from the adjustment terminal to the output (see figure 2). improved internal circuitry eliminates the need for this diode when the adjustment pin is bypassed with a capaci - tor to improve ripple rejection. if a ver y large output capacitor is used , such as a 100f shown in figure 2, the regulator could be damaged or destroyed if the input is accidentally shorted to ground or crowbarred , due to the output capacitor discharging into the output terminal of the regulator . to prevent this, a diode d1 as shown, is recommended to safely discharge the capacitor. figure 2 lt338a d1 1n4002 v in r1 not needed 138a/338a f02 v out adj v out v in r2 c adj 10f c out 100f + load regulation because the lt138a is a three-terminal device, it is not possible to provide true remote load sensing. load regula - tion will be limited by the resistance of the wire connecting the regulator to the load. the data sheet specification for load regulation is measured at the bottom of the package. negative side sensing is a true kelvin connection, with the bottom of the output divider returned to the negative side of the load. although it may not be immediately obvious, best load regulation is obtained when the top of the resis - tor divider, r1, is connected directly to the case not to the load . this is illustrated in figure 3 . if r1 were connected to the load, the effective resistance between the regulator and the load would be: r p r2 + r1 r1 ? ? ? ? ? ? ,r p = parasitic line resistance connected as shown, r p is not multiplied by the divider ratio. r p is about 0.004 per foot using 16 gauge wire. this translates to 4mv/ft at 1a load current, so it is important to keep the positive lead between regulator and load as short as possible, and use large wire or pc board traces. lt138a/lt338a lm138/lm338 138afd
8 for more information www.linear.com/lt138a applica t ions in f or m a t ion figure 3. connections for best load regulation lt338a r p parasitic line resistance v in r1 connect r1 to case connect r2 to load 138a/338a f03 v out adj v in r l r2 typical a pplica t ions improving ripple rejection 1.2v to 25v adjustable regulator lt338a v in r1 121 1% r2 365 1% 1f *c1 improves ripple rejection, x c should be small compared to r2 c l * 10f 138a/338a ta03 v out adj 5v v in + + lt338a v in r1 240 c1* 1f needed if device is far from filter capacitors optional, improves transient response r2 5k 138a/338a ta04 v out adj v out ? v in + c2** 1f * ** + ? v out = 1.25v r2 r1 1 + ( ) lt138a/lt339a lm138/lm338 138afd
9 for more information www.linear.com/lt138a t ypical a pplica t ions 5v regulator with shutdown temperature compensated lead acid battery charger remote sensing lt338a v in 121 1% 1f 138a/338a ta05 v out adj 5v 2n3904 v in ttl 365 1% 1k 1k + lt338a v in 243 1% 138a/338a ta07 v out 2n3906 adj 3a 50k 2k 10k 12v 50 lt338a v in v in return v out adj + ? + lm301a v in 100pf 138a/338a ta06 1k 25 r p (max drop 300mv) 25 121 r l 365 5f 6 1 2 7 v out 5v return 3 8 4 lt138a/lt338a lm138/lm338 138afd
10 for more information www.linear.com/lt138a s che m a t ic diagra m lt138a/lt338a 200 300 v in v out adj 120 3 16k q27 q26 q22 q25 12k 1.6k 6.7k 20k 5.6k 50 190 310 310 c3 5pf d1 18k q24 q23 q21 q19 q13 q9 q6 q4 q1 q18 q16 q28 160 160k 0.01 138a/338a ss 400 2.4k 3k 12.4k 130 4k 30k 12k 5.1k 4.1k 10 4.1k 180 q1 160k d2 q14 q20 q17 c2 30pf c1 30pf + + q12 q7 q10 q8 q3 q2 q15 q11 q5 lt138a/lt339a lm138/lm338 138afd
11 for more information www.linear.com/lt138a p ackage descrip t ion obsolete package please refer to http://www .linear.com/designtools/packaging/ for the most recent package drawings. k package 2-lead to-3 metal can (reference ltc dwg # 05-08-1310) k2 (to-3) 1098 0.038 ? 0.043 (0.965 ? 1.09) 0.060 ? 0.135 (1.524 ? 3.429) 0.320 ? 0.350 (8.13 ? 8.89) 0.420 ? 0.480 (10.67 ? 12.19) 0.760 ? 0.775 (19.30 ? 19.69) 0.490 ? 0.510 (12.45 ? 12.95) r 0.167 ? 0.177 (4.24 ? 4.49) r 0.151 ? 0.161 (3.86 ? 4.09) dia, 2plcs 1.177 ? 1.197 (29.90 ? 30.40) 0.655 ? 0.675 (16.64 ? 17.15) 0.067 ? 0.077 (1.70 ? 1.96) 0.210 ? 0.220 (5.33 ? 5.59) 0.425 ? 0.435 (10.80 ? 11.05) lt138a/lt338a lm138/lm338 138afd
12 for more information www.linear.com/lt138a obsolete package please refer to http://www .linear.com/designtools/packaging/ for the most recent package drawings. .170 (4.32) max .325 (8.255) .580 (14.732) .560 (14.224) .170 ? .2oo (4.32 ? 5.08) mounting hole .115 ? .145 (2.92 ? 3.68) dia .580 ? .6oo (14.73 ? 15.24) .830 ? .870 (21.08 ? 22.10) .780 ? .800 (19.81 ? 20.32) .620 ? .64o (15.75 ? 16.26) .215 (5.46) bsc .113 ? .123 (2.87 ? 3.12) .042 ? .052 (1.07 ? 1.32) .074 ? .084 (1.88 ? 2.13) .187 ? .207 (4.75 ? 5.26) .060 ? .080 (1.52 ? 2.03) 18 ? 22 3 ? 7 .087 ? .102 (2.21 ? 2.59) .020 ? .040 (0.51 ? 1.02) ejector pin marks .105 ? .125 (2.67 ? 3.18) dia p3 0801 .098 (2.489) .124 (3.149) .700 (17.780) .275 (6.985) bottom view of to-3p hatched area is solder plated copper heat sink p package 3-lead plastic to-3p (similar to to-247) (reference ltc dwg # 05-08-1450) p ackage descrip t ion lt138a/lt339a lm138/lm338 138afd
13 for more information www.linear.com/lt138a 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 . r evision h is t ory rev date description page number d 05/15 obsolete packaged parts. 1, 2, 12 (revision history begins at rev d) lt138a/lt338a lm138/lm338 138afd
14 for more information www.linear.com/lt138a ? linear technology corporation 1991 lt 0515 rev d ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/lt138a r ela t e d p ar t s typical a pplica t ion part number description comments lt1083/lt1084/ lt1085 3a/5a/7.5a low dropout regulators fixed outputs, v in up to 30v lt1580 7a fast transient response regulator with 0.7v dropout for 3.3v to 2.xxv applications lt1581 10a fast transient response regulator for 3.3v to 2.xxv applications lt1584/lt1585/ lt1587 7a/4.6a/3a low dropout fast transient response regulator for 1.2v to 3.3v outputs from 5v lt1764 3a fast transient response regulator dropout voltage 340mv, low noise: 40v rms lamp flasher automatic light control protected high current lamp driver lt338a v in 138a/338a ta08 v out adj 12k 1f 10f 12v 15v 12k 1k off 12k + + 10f 10f + 2n3904 + lt338a v in 138a/338a ta09 v out adj 1.2k lt338a v out 12v 5a 138a/338a ta10 v in ttl or cmos adj 15v 10k lt138a/lt339a lm138/lm338 138afd

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