LM138/LM338 General Description The LM138 series of adjustable 3-terminal positive voltage regulators is capable of supplying in excess of 5A over a 1.2V to 32V output range. They are exceptionally easy to use and require only 2 resistors to set the output voltage. Careful circuit design has resulted in outstanding load and line regulation comparable to many commercial power supplies. The LM138 family is supplied in a standard 3-lead transistor package. A unique feature of the LM138 family is time-dependent cur- rent limiting. The current limit circuitry allows peak currents of up to 12A to be drawn from the regulator for short periods of time. This allows the LM138 to be used with heavy tran- sient loads and speeds start-up under full-load conditions. Under sustained loading conditions, the current limit de- creases to a safe value protecting the regulator. Also in- cluded on the chip are thermal overload protection and safe area protection for the power transistor. Overload protection remains functional even if the adjustment pin is accidentally disconnected. Normally, no capacitors are needed unless the device is situ- ated more than 6 inches from the input filter capacitors in which case an input bypass is needed. An output capacitor can be added to improve transient response, while bypass- ing the adjustment pin will increase the regulators ripple re- jection. AY ational Semiconductor 5-Amp Adjustable Regulators May 1998 Besides replacing fixed regulators or discrete designs, the LM138 is useful in a wide variety of other applications. Since the regulator is floating and sees only the input-to-output differential voltage, supplies of several hundred volts can be regulated as long as the maximum input to output differential is not exceeded, i.e., do not short-circuit output to ground. The part numbers in the LM138 series which have a K suffix are packaged in a standard Steel TO-3 package, while those with a T suffix are packaged in a TO-220 plastic package. The LM138 is rated for -55C <T, < +150C, and the LM338 is rated for C <T, $+125C. Features w Guaranteed 7A peak output current @ Guaranteed 5A output current @ Adjustable output down to 1.2V @ Guaranteed thermal regulation @ Current limit constant with temperature w P* Product Enhancement tested w Output is short-circuit protected Applications @ Adjustable power supplies @ Constant current regulators w Battery chargers (TO-3 STEEL) Metal Can Package ADJUSTMENT VIN CASE IS OUTPUT Ds009060-30 Bottom View Order Number LM138K STEEL or LM338K STEEL See NS Package Number K02A Connection Diagrams (See Physical Dimension section for further information) (TO-220) Plastic Package Vout L O > VIN > Vout > ADS DSo09060-31 Front View Order Number LM338T See NS Package Number T03B 1999 National Semiconductor Corporation DSoo0s060 www.national.com siojeinboy aiqeisnipy dwiy-s sseW1/SELINT(Note 4) Power Dissipation Input/Output Voltage Differential Storage Temperature Absolute Maximum Ratings (note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Electrical Characteristics Specifications with standard type face are for T; = 25C, and those with boldface type apply over full Operating Tempera- ture Range. Unless otherwise specified, Vij - Vout = 5V; and lout = 10 mA. (Note 2) Internally limited +40V, -0.3V -65C to +150C Lead Temperature ESD Tolerance Metal Package (Soldering, 10 seconds) Plastic Package (Soldering, 4 seconds) Operating Temperature Range -5C <T, $+150C OC <T, <+125C LM138 LM338 300C 260C TBD 3V < (Vin - Vour) $ 35V Symbol Parameter Conditions LM138 Units Min Typ Max VrRer Reference Voltage 3V < (Vin - Vout) = 35V, 1.19 1.24 1.29 Vv 10 mA Iout S$ 5A, P s 50W Veaine Line Regulation 3V < (Vin - Vout) = 35V (Note 3) 0.005 0.01 IN 0.02 0.04 KIN Vrtoap Load Regulation 10 MA Igu7 5A (Note 3) 0.1 0.3 % 0.3 0.6 % Thermal Regulation 20 ms Pulse 0.002 0.01 %i\N lapu Adjustment Pin Current 45 100 HA Alaps Adjustment Pin Current Change 10 MA Iguz 5A, 0.2 5 HA 3V < (Vin - Vout) $ 35V AVart Temperature Stability Twin & Ta = Tax 1 % ILoap(Min) Minimum Load Current Vin - Vout = 35V 3.5 5 mA lot Current Limit Vin Vour = 10V DC 5 8 A 0.5 ms Peak 7 12 A Vin - Vout = 30V 4 4 A Vu RMS Output Noise, % of Vout 10 Hz <f < 10 kHz 0.003 % AVA Ripple Rejection Ratio Vout = 10V, f = 120 Hz, Cap, = 0 UF 60 dB AVIN Vour = 10V, f = 120 Hz, Capy = 10 UF 60 75 dB Long-Term Stability Ty = 125C, 1000 Hrs 0.3 4 % Bic Thermal Resistance, K Package 4 CW Junction to Case 85a Thermal Resistance, Junction to K Package 35 CW Ambient (No Heat Sink) Electrical Characteristics Symbol Parameter Conditions LM338 Units Min Typ Max VrRer Reference Voltage 3V < (Vin - Vout) = 35V, 1.19 1.24 1.29 Vv 10 mA Ioyr S$ 5A, P s 50W Veaine Line Regulation 3V < (Vin - Vout) = 35V (Note 3) 0.005 0.03 SIN 0.02 0.06 KIN Vrtoap Load Regulation 10 mA Iguz = 5A (Note 3) 0.1 0.5 % 0.3 1 % Thermal Regulation 20 ms Pulse 0.002 0.02 %i\N lapu Adjustment Pin Current 45 100 HA Alapu Adjustment Pin Current Change 10 mA Igurz = BA, 02 5 yA www.national.comElectrical Characteristics (continued) Symbol Parameter Conditions LM338 Units Min Typ Max AVart Temperature Stability Twin Ta & Tax 1 % lLoap(Min) Minimum Load Current Vin - Vout = 35V 3.5 10 mA lot Current Limit Vin - Vout = 10V DC 5 8 A 0.5 ms Peak 12 A Vin - Vout = 30V 4 A Vn RMS Output Noise, % of Vout 10 Hz <f< 10 kHz 0.003 % AVA Ripple Rejection Ratio Vout = 10V, f = 120 Hz, Capy = 0 UF 60 dB AVIN Vour = 10V, f = 120 Hz, Capy = 10 UF 60 75 dB Long-Term Stability Ty = 125C, 1000 hrs 0.3 4 % Bic Thermal Resistance K Package 4 CW Junction to Case T Package 4 CW 85a Thermal Resistance, Junction to K Package 35 CW Ambient (No Heat Sink) T Package 50 CW Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is in- tended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: These specifications are applicable for power dissipations up to 50W for the TO-3 (K) package and 25W for the TO-220 (T) package. Power dissipation is guaranteed at these values up to 15V input-output differential. Apove 15V differential, power dissipation will be limited by internal protection circuitry. All limits (i.e., the numbers in the Min. and Max. columns) are guaranteed to National's AOQL (Average Outgoing Quality Level). Note 3: Regulation is measured at a constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are covered under the specifications for thermal regulation. Note 4: Refer to RETS138K drawing for military specifications of LM138K. Typical Performance Characteristics Current Limit OUTPUT CURRENT {A} aa 10 10 100 TIME (ms) DS009060-32 Load Regulation 02 at 03 }in= 15V Vout = 10V PRELOAD = 50 OUTPUT VOLTAGE DEVIATION (%) L 2S 75-50-25 D 25 50 75 100 125 150 TEMPERATURE {f) DS009060-35 Current Limit 16 OC CURRENT LIMIT Tease = 25C =z 2 =o E =z a & 5S 8 3 E ] = 5 s 4 a 10 20 40 40 INPUT-OUTPUT DIFFERENTIAL (V} DS009060-33 Dropout Voltage 4 INPUT-OUTPUT DIFFERENTIAL (V)} 1 -75-5D-25 0 25 50 75 100 126 150 TEMPERATURE (C} DS009060-36 Current Limit OUTPUT CURRENT (A) 01 1 10 100 TIME (ms) DS009060-34 Adjustment Current 55 50 45 ADJUSTMENT CURRENT (vA) 75 50-25 0 25 5D 75 100 125 150 TEMPERATURE (C) DS009060-37 www.national.comTemperature Stability 1.260 1.250 1.240 1.230 REFERENCE VOLTAGE (V} i g Ss 1.210 -75-50-25 D 25 50 75 100 126 150 TEMPERATURE (C) Ds009060-38 Ripple Rejection 100 80 60 Caps= 40 RIPPLE REJECTION (dB) Vin - Your = = 2A = 120 Hz 0 66) 610) 615 620 2688 QUTPUT VOLTAGE {V) DSoogo60-41 Line Transient Response 15 10 = 1 HF; Cy = 10 uF \ Io e eon OUTPUT VOLTAGE DEVIATION {V) 4 Vout = WV -1.0 = 50 o = 256 g _ 1.5 = 10 $$ Fz os i Be oo . a rT es) TIME {zs} Application Hints put voltage of Typical Performance Characteristics (continued) Output Impedance 101 10-1 2 OUTPUT IMPEDANCE (22) 5 3 o i 10 100 1k 10k = 100k = 1M FREQUENCY (Hz) DS009060-39 Ripple Rejection 100 40 RIPPLE REJECTION (dB) Tease = 25C 10 100 1k 1k =6100k = =1M FREQUENCY (Hz) Dsoog060-42 Minimum Operating Current 4 QUIESCENT CURRENT (mA) n T-26c 0 10 20 40 40 INPUT-OUTPUT DIFFERENTIAL (V)} DSoog060-40 Ripple Rejection 80 gz 1 2 S & a 60 al = wi 4 = oso f Vins lev = Vout = 10 f= 120 Hz Trase = 25C 40 ou 1 10 OUTPUT CURRENT (A) DSoog060-43 Load Transient Response eo nNs uw OUTPUT VOLTAGE | OUTPUT CURRENT (4) Devan TigR (V) ocneaead db 40 Dsoo9060-44 In operation, the LM138 develops a nominal 1.25V reference voltage, Vref, between the output and adjustment terminal. The reference voltage is impressed across program resistor R1 and, since the voltage is constant, a constant current I, then flows through the output set resistor R2, giving an out R2 Vout = Vrer (1 + =) + lapgR2. 10 20 30 40 TIME (js) DS009060-45 www.national.comApplication Hints (Continue) LM338 Om Vin = Yout Vout FIGURE 1. Dso09060-6 Since the 50 YA current from the adjustment terminal repre- sents an error term, the LM138 was designed to minimize lapy and make it very constant with line and load changes. To do this, all quiescent operating current is returned to the output establishing a minimum load current requirement. If there is insufficient load on the output, the output will rise. External Capacitors An input bypass capacitor is recommended. A 0.1 UF disc or 1 UF solid tantalum on the input is suitable input bypassing for almost all applications. The device is more sensitive to the absence of input bypassiing when adjustment or output capacitors are used but the above values will eliminate the possiblity of problems. The adjustment terminal can be bypassed to ground on the LM138 to improve ripple rejection. This bypass capacitor prevents ripple from being amplified as the output voltage is increased. With a 10 UF bypass capacitor 75 dB ripple rejec- tion is obtainable at any output level. Increases over 20 UF do not appreciably improve the ripple rejection at frequen- cies above 120 Hz. If the bypass capacitor is used, it is sometimes necessary to include protection diodes to prevent the capacitor from discharging through internal low current paths and damaging the device. In general, the best type of capacitors to use are solid tanta- lum. Solid tantalum capacitors have low impedance even at high frequencies. Depending upon capacitor construction, it takes about 25 UF in aluminum electrolytic to equal 1 YF solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies; but some types have a large decrease in capacitance at frequencies around 0.5 MHz. For this reason, 0.01 LF disc may seem to work better than a 0.1 LF disc as a bypass. Although the LM138 is stable with no output capacitors, like any feedback circuit, certain values of external capacitance can cause excessive ringing. This occurs with values be- tween 500 pF and 5000 pF. A1 uF solid tantalum (or 25 UF aluminum electrolytic) on the output swamps this effect and insures stability. Load Regulation The LM138 is capable of providing extremely good load regulation but a few precautions are needed to obtain maxi- mum performance. The current set resistor connected be- tween the adjustment terminal and the output terminal (usu- ally 240Q) should be tied directly to the output of the regulator (case) rather than near the load. This eliminates line drops from appearing effectively in series with the refer- ence and degrading regulation. For example, a 15V regula- tor with 0.05 resistance between the regulator and load will have a load regulation due to line resistance of 0.05Q x I,. If the set resistor is connected near the load the effective line resistance will be 0.059 (1 + R2/R1) or in this case, 11.5 times worse. Figure 2 shows the effect of resistance between the regula- tor and 240Q set resistor. LM338 Rs Vin=Tin- = Vout AA Vout ADJ S$ RI > S$ 120 > < ge Dsoog060-7 FIGURE 2. Regulator with Line Resistance in Output Lead With the TO-3 package, it is easy to minimize the resistance from the case to the set resistor, by using 2 separate leads to the case. The ground of R2 can be returned near the ground of the load to provide remote ground sensing and improve load regulation. Protection Diodes When external capacitors are used with any IC regulator it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator. Most 20 UF capacitors have low enough internal series resistance to deliver 20A spikes when shorted. Although the surge is short, there is enough energy to damage parts of the IC. When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage of the regu- lator, and the rate of decrease of Vy. In the LM138 this dis- charge path is through a large junction that is able to sustain 25A surge with no problem. This is not true of other types of positive regulators. For output capacitors of 100 UF or less at output of 15V or less, there is no need to use diodes. The bypass capacitor on the adjustment terminal can dis- charge through a low current junction. Discharge occurs when either the input or output is shorted. Internal to the LM138 is a 50 resistor which limits the peak discharge cur- rent. No protection is needed for output voltages of 25V or less and 10 UF capacitance. Figure 3 shows an LM138 with protection diodes included for use with outputs greater than 25V and high values of output capacitance. www.national.comApplication Hints (Continued) Dso09060-8. D1 protects against C1 D2 protects against C2 R2 Vout = 1.25V (: + =) + lapyR2 FIGURE 3. Regulator with Protection Diodes www.national.com 6Typical Applications 1.2V25V Adjustable Regulator Regulator and Voltage Reference LM338 LNI338 Vin > 28V Vin apsotT Vouttt Vinqin Vout Vout = 15V $ ni ADJ out S 120 gsr + S12 cis c2t 4 , 1 pF Sox > sk > sr S 14k 2" @ Vrer = 6.95V - [s009060-1 rao M328 Temperature Controller 1 LM338 DSo09060-3. Vin =a] IN OUT Vout IN ADs ou gsr > < S12 a HEATER LM334 100K a GAIN 79 R2 80 DSo009060-10 Full output current not available at high input-output voltages Optional improves transient response. Output capacitors in the range of 1 UF to 1000 LF of aluminum or tantalum electrolytic are commonly used to provide improved output impedance and rejection of transients. *Needed if device is more than 6 inches from filter capacitors. R2 +tVour = 1.25V (1 + =) + lapy (Ra) **R1 = 2400 for LM138. R1, R2 as an assembly can be ordered from Bourns: MIL part no. 7105A-AT2-502 COMM part no. 7105A-AT7-502 7 www.national.comSchematic Diagram vos AQ rav NA? pt AND, $ c00 > Sse ava AA. Wr sos > < Seu acy 0 At wD yeh fa Ozu , w os ANA agL zu > ow S 4! 400z tzu leu > 9 gu Aca a0 nes ws 9 840 voy ta 7 za guy z0 guy su > 5z0 bw e OLE 6lu o10 ; $ 061 ole Ore zz ws S ze su ; ry ey zu td Ny e 4 o www.national.comTypical Applications Precision Power Regulator with Low Temperature Coefficient LM338 Vin IN ourT| Vour =4V DJ OUTPUT ADJUST = DSoog060-12 * Adjust for 3.75 across R1 Slow Turn-On 15V Regulator Adjustable Regulator with Improved Ripple Rejection LM338 LM338 Vv Vv Vout Vv Vin Vout Vin IN ADs out Ny IN ADJ AIt* o1* c2 a E 120 1nago2 O.1 pF Aa [ e 1Na002 L ca = q = 1 pFt - + > C1 R2 10 uF Sk = DS009060-14 DS009060-13 *Solid tantalum *Discharges C1 if output is shorted to ground **R1 = 2400 for LM138 High Stability 10V Regulator Digitally Selected Outputs LM338 LM338 VIN Vv Vv Vv IN OUT Vv Vv Vv VouT 15V ADs OUT 10V IN (N ADJ out ou Ss R1** C1 s 120 < 1.5k > 1% > > LM329B R2* = a = DS009060-15 INPUTS DS009060-16 *Sets maximum Vout **R1 = 2400 for LM138 9 www.national.comTypical Applications (continued) 15A Regulator LM338 RS 0.1 Vv Vout VWA=1 IN apy OUT : RG 0.1 Vin -? N? -W-e Vin, yout Vour* > RT * 120 C1 tt + c2 10pF OTS 22 uF RB 2k _ DSoog060-17 * Minimum load 100 mA 5V Logic Regulator with Electronic Shutdown** Light Controller LM338 LM338 Vv ViIn==7IN OUT Vn 7V-35V Vin Vout ouT 1N ADJ 5V ADJ 2k TTL ae ps00s060-11 DS009060-18. ** Minimum output ~ 1.2V www.national.com 10Typical Applications (continued) 0 to 22V Regulator LM338 VIN Vv Vv 25V iN ADs OUT Vout RI* 100 R2 > 2k -10V DSo009060-19. * Ri = 2400, R2 = 5k for LM138 Full output current not available at high input-output voltages 12V Battery Charger 500 Ww RG 0.2 Vin = 18V LM338 > W479 ) + LEO ne , TO 12V a1 BATTERY 2N2905 > oA ek + 0.1 uF Ne ou uw oT -o + o | DSo009060-20 www.national.comTypical Applications (continued) Adjustable Current Regulator Precision Current Limiter LM338 &, Lwi338 OUT Lk ae Vin 4 Yin any OUT p ~T_ 0A-5A Vinyin Your P'ouT= = ADJ Ri Al | $ R2 | > 150 DSoos060-22 v ap, 'N LM117 Vout R3 120 > = v- -5V TO -10V DSoogos0-21 5A Current Regulator Tracking Preregulator LM338 R2 720 VIN Vin Your ADJ ct 240 a 2 0. 240 LM338 0.1 we > ow Lr ADI > VIN v Vv Vin Vout Vo = UT IN OUT apd P LM338 S R3 LOAD S 120 ct + 0.1 HF 1 pF Ra Soreur F ADJUST Ds009060-23 DSoog060-24 Adjusting Multiple On-Card Regulators with Single Control* LNi338 Vin "in Vout v Vinqin Your Vout Vinws Yin Vout Vout IN And out VIN ADJ out YIN AD QUT 14002 Rt 1N4002 120 q R2 1k DSo0g060-25 + Minimum load 10 mA * All outputs within 100 mV www.national.com 12Typical Applications (continued) Power Amplifier 35V 22 MJ4502 1000 4F Ay = 1, Re = 10k, Cp = 100 pF Ay = 10, Rp = 100k, Cp = 10 pF Bandwidth > 100 kHz Distortion < 0.1% Simple 12V Battery Charger LM338 Rg* 01 VIN Vin Vout ADJ 1000,F** R2 *Rssets output impedance of charger Zout = As (1 + me) Use of Rg allows low charging rates with fully charged battery. **The 1000 UF is recommended to filter out input transients LM395 Hew, LM338 Dso09060-27 Dso09060-28 www.national.comTypical Applications (continued) Adjustable 15A Regulator Current Limited 6V Charger * Minimum load 100 mA V 0.1 LM338 IN LM338 NA, ~ ov 10 a4 Yin, Your ? | ADL 01 [+ M338 ANA 1000,F** rT q 1.1k LM338 0.1 Min four MAA O 450 TO 25V 2nz2z2 02* < > > 100 > si Dso0g060-29 2N2905 4 * Set max charge current to 3A 7 ** THE 1000 uF is recommended to filter out input transients. "2 LM308 > Ss 8 3 150 s* + AAA 200 pF 2 1.5k 10A Regulator R LM338 a. ANN Vout ADJ R LM338 0.1 o AAA ouTPuT* VIN Vv any OU f 1.2V To 20V $A $ 120 co th 1 WF > S$ R2 jer DSoogo60-2 www.national.comPhysical DimensiONS inches (millimeters) unless otherwise noted 0.420-0.500 0.325-0.352 [10.67-12.70] [8.26-8.94] 0.980-1.020 0.060-0.070 0.151-0.161 [24.89-25.91] >| -_ - xB [3.84-4.09] || [1.52-1.78] - -4 0.495-0.510 [12.57-12.95] nh 0.660-0.670 [16.76-17.02] g ,0-880-0.915 [22.35-23.24] 0.760-0.775 _ [19.30-19.69] 1.177-1.197 [29.90-30.40] oy g 0:038-0.043 | _ [0.97-1.09] - UNCONTROLLED | 0.168-0.178 LEAD DIA 0.210-0.220 2xR 0.025 0.116 4.27-4,52 : [5.33-5.59] | [ ] [o.64] MAXI PT po gs] MAX 0.425-0.435 SEATING PLANE ~~ Ko2A (REV 6) | (ost 80-11.05] 2 Lead TO-3 Metal Can Package (K) Order Number LM138K or LM338K STEEL NS Package Number K02A 0.240-0.260 9.330-0.350 [6.10-6.60] [8.38-8.89] 9,100-0,120 0.149-0.153 [2.54-3.05] / [3.78-3.89] aors eer 0.400 o'o08 _ L _ _ __[2,29-2,79] 0.190-0.210 [10.16 7238] a | | [4.83-5.33] L 0.048-0.055 I / 0.130-0.160 15 [1,22-1.40] PIN #1 1D [3.30-4.06] TYP 1,005-1.035 0.027-0.037 [25.53-26.29] , [0.69-0.94] TYP 0.525-0.555 yoo (0-38 hos ] [4.45-4.70] t | +f AD ee 13.34-14.10] ane 0.015 950; [0- [ 048-0.052 [1.22-1.32] TAPERED SIDES 1 mlb \ ] SEATING PLANE 3 Lead Molded TO-220 (T) Order Number LM338T NS Package Number T03B 0.010 L- 0,105 *5o45 [2-67 550 ] 40.25 T03B (REV L) www.national.comLM138/LM338 5-Amp Adjustable Regulators LIFE SUPPORT POLICY NATIONALS PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DE- VICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMI- CONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or sys- 2. tems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose fail- ure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury A critical component is any component of a life support device or system whose failure to perform can be rea- sonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. to the user. National Semiconductor National Semiconductor Corporation Europe Asia Pacific Customer Japan Ltd. Americas Fax: +49 (0) 1 80-530 85 86 Response Group Tel: 81-3-5639-7560 Tel: 1-800-272-9959 Email: europe.suppori@nsc.com Tel: 65-2544466 Fax: 81-3-5639-7507 Fax: 1-800-737-7018 Deutsch Tel: +49 (0) 1 80-530 85 85 Fax: 65-2504466 Email: support@nsc.com English Tel: +49 (0) 1 80-532 78 32 Email: sea.support@nsc.com Frangais Tel: +49 (0) 1 80-532 93 58 www.national.com Italiano Tel: +49 (0) 1 80-534 16 80 National does not assume any responsibilily for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.