LT138A/LT338A LM138/LM338 5A Positive Adjustable Voltage Regulator U FEATURES DESCRIPTIO The LT(R)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 limiting circuitry allowing large transient load currents to be handled for short periods. Transient load currents of up to 12A can be supplied without limiting, eliminating the need for a large output capacitor. Guaranteed 1% Initial Tolerance Guaranteed 0.3% Load Regulation Guaranteed 5A Output Current 100% Thermal Limit Burn-In 12A Transient Output Current U APPLICATIO S High Power Linear Regulator Battery Chargers Power Driver Constant-Current Regulator The LT138A is an improved version of the popular LM138 with improved circuit design and advanced process techniques to provide superior performance and reliability. The graph below shows the significant improvement in output voltage tolerance achieved by using the LT138A or LT338A. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATIO Parallel Regulators for Higher Current* Output Voltage Error 12 VIN VIN 0.01** VOUT 5V 8A ADJ LT350A VIN 0.016** VOUT ADJ 121 1% 365 1% 11 OUTPUT VOLTAGE ERROR (%) LT338A 10 9 2% RESISTORS 8 7 1% RESISTORS 6 LM338 LM338 LT338A 5 4 2% RESISTORS 3 LT338A 1% RESISTORS 2 1 0 138/338 TA01 *THIS CIRCUIT WILL NOT WORK WITH LM VERSION DEVICES **CURRENT SHARING RESISTORS DEGRADE REGULATION TO 1% 1 10 OUTPUT VOLTAGE (V) 100 138A/338A TA02 1 LT138A/LT338A LM138/LM338 RATI GS (Note 1) Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C U W Power Dissipation .............................. Internally Limited Input-to-Output Voltage Differential ........................ 35V Operating Junction Temperature Range LT138A/LM138 ............................... - 55C to 150C LT338A/LM338 ................................... 0C to 125C UU W W AXI U U ABSOLUTE PRECONDITIONI G 100% Thermal Limit Burn-In U W U PACKAGE/ORDER I FOR ATIO BOTTOM VIEW ORDER PART NUMBER VIN 2 CASE IS OUTPUT 1 ADJ ORDER PART NUMBER FRONT VIEW LT138AK LT338AK LM138K LM338K 3 VOUT 2 VIN 1 ADJ LM338P P PACKAGE 3-LEAD PLASTIC TO-3P TJMAX = 125C, JA = 45C/ W K PACKAGE 2-LEAD TO-3 METAL CAN TJMAX = 150C, JA = 35C/ W, JC = 1C/ W (LT138A/LT138) TJMAX = 125C, JA = 35C/ W, JC = 1C/ W (LT338A/LT338) Consult factory for Industrial grade parts. ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 2) SYMBOL PARAMETER VREF Reference Voltage CONDITIONS IOUT = 10mA, TJ = 25C 3V (VIN - VOUT) 35V, 10mA IOUT 5A, P 50W VOUT VIN VOUT IOUT Line Regulation Load Regulation 20ms Pulse Ripple Rejection VOUT = 10V, f = 120Hz CADJ = 0F CADJ = 10F LM138 TYP MAX UNITS 1.19 1.24 1.29 V 1.250 1.262 1.250 1.270 0.005 0.02 0.01 0.04 0.005 0.02 0.01 0.04 %/V %/V 5 0.1 15 0.3 5 0.1 15 0.3 mV % 20 0.3 30 0.6 20 0.3 30 0.6 mV % 0.002 0.01 0.002 0.01 %/W MIN 1.225 10mA IOUT 5A, (Note 3) VOUT 5V VOUT 5V Thermal Regulation LT138A TYP MAX 1.238 60 60 75 V 60 60 75 dB dB 45 100 45 100 A 10mA IOUT 5A, 3V (VIN - VOUT) 35V 0.2 5 0.2 5 A Minimum Load Current (VIN - VOUT) = 35V 3.5 5 3.5 5 mA Current Limit (VIN - VOUT) 10V DC 0.5ms Peak IADJ Adjust Pin Current IADJ Adjust Pin Current Change (VIN - VOUT) = 30V, TJ = 25C 2 3V (VIN - VOUT) 35V, (Note 3) VOUT 5V VOUT 5V ISC MIN 5 6 8 12 1 5 6 2 8 12 A A 1 A LT138A/LT338A LM138/LM338 ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 2) SYMBOL VOUT Temp VOUT Time PARAMETER CONDITIONS MIN Temperature Stability Long-Term Stability TA = 125C, 1000 Hours en RMS Output Noise (% of VOUT) 10Hz f 10kHz JC Thermal Resistance Junction-to-Case LT138A TYP MAX MIN LM138 TYP 1 2 1 0.3 1 0.3 0.001 K Package MAX % 1 % 1 C/W MAX UNITS 0.003 1 UNITS % The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 2) LT338A TYP MAX SYMBOL PARAMETER CONDITIONS MIN VREF Reference Voltage IOUT = 10mA 1.238 1.250 1.262 1.225 1.250 1.270 0.005 0.02 3V (VIN - VOUT) 35V, 10mA IOUT 5A, P 50W VOUT VIN VOUT IOUT Line Regulation 3V (VIN - VOUT) 35V, (Note 3) Load Regulation 10mA IOUT 5A, (Note 3) VOUT 5V VOUT 5V VOUT 5V VOUT 5V Thermal Regulation 20ms Pulse Ripple Rejection VOUT = 10V, f = 120Hz CADJ = 0F CADJ = 10F 60 MIN LM338 TYP V 1.24 1.29 V 0.01 0.04 0.005 0.02 0.03 0.06 %/V %/V 5 0.1 15 0.3 5 0.1 25 0.5 mV % 20 0.3 30 0.6 20 0.3 50 1 mV % 0.002 0.02 0.002 0.02 %/W 60 75 1.19 60 60 75 dB dB IADJ Adjust Pin Current 45 100 45 100 A IADJ Adjust Pin Current Change 10mA IOUT 5A, 3V (VIN - VOUT) 35V 0.2 5 0.2 5 A Minimum Load Current (VIN - VOUT) = 35V 3.5 10 3.5 10 mA Current Limit (VIN - VOUT) 10V DC 0.5ms Peak ISC (VIN - VOUT) = 30V, TJ = 25C VOUT Temp VOUT Time Temperature Stability Long-Term Stability TA = 125C, 1000 Hours en RMS Output Noise (% of VOUT) 10Hz f 10kHz JC Thermal Resistance Junction-to-Case K Package Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: Unless otherwise specified, these specifications apply: VIN - VOUT = 5V and IOUT = 2.5A. These specifications are applicable for power dissipations up to 50W. 5 6 8 12 5 6 8 12 A A 1 2 1 A 1 2 1 % 0.3 1 0.3 0.001 1 % 1 C/W 0.003 1 % 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. 3 LT138A/LT338A LM138/LM338 U W TYPICAL PERFOR A CE CHARACTERISTICS Load Regulation 4 0 IOUT = 3A - 0.1 IOUT = 5A - 0.2 - 0.3 - 0.4 -75 - 50 - 25 VOUT = 100mV 60 3 IOUT = 5A IOUT = 3A 2 IOUT = 1A 1 -75 - 50 - 25 0 25 50 75 100 125 150 TEMPERATURE (C) Temperature Stability 40 1.260 1.250 1.240 VIN = 15V VOUT = 10V IOUT = 500mA 1 CADJ = COUT = 0F 0.1 0.01 CADJ = COUT = 10F 0.0001 4 TJ = 150C TJ = 25C 3 TJ = - 55C 2 1 0 10 100 10k 1k FREQUENCY (Hz) 100k 1M 25 30 35 5 10 15 20 INPUT-OUTPUT DIFFERENTIAL (V) 0 138/338 G05 Ripple Rejection Ripple Rejection 80 100 CADJ = 10F CADJ = 10F 80 CADJ = 0F 60 40 VIN - VOUT = 5V IOUT = 500mA f = 120Hz TJ = 25C 20 15 10 25 OUTPUT VOLTAGE (V) 30 35 138A/338A G07 4 60 CADJ = 0F 40 20 0 CADJ = 10F RIPPLE REJECTION (dB) RIPPLE REJECTION (dB) RIPPLE REJECTION (dB) 80 5 40 138A/338A G06 Ripple Rejection 100 0 125 Minimum Operating Current 138A/338A G04 20 25 75 TEMPERATURE (C) 5 0.001 25 50 75 100 125 150 TEMPERATURE (C) -25 138A/338A G03 Output Impedance 10 OUTPUT IMPEDANCE () REFERENCE VOLTAGE (V) 45 138/338 G02 1.270 0 50 30 -75 0 25 50 75 100 125 150 TEMPERATURE (C) 138/338 G01 1.230 -50 -25 55 35 QUIESCENT CURRENT (mA) 0.1 Adjustment Current 65 ADJUSTMENT CURRENT (A) VIN = 15V VOUT = 10V PRELOAD = 50mA INPUT-OUTPUT DIFFERENTIAL (V) OUTPUT VOLTAGE DEVIATION (%) 0.2 Dropout Voltage 0 VIN = 15V VOUT = 10V IOUT = 0.2A 10 100 70 CADJ = 0F 60 50 40 10k 1k FREQUENCY (Hz) 100k 1M 138A/338A G08 VIN = 15V VOUT = 10V f = 120Hz TCASE = 25C 0.1 1 OUTPUT CURRENT (A) 10 138/338 G09 LT138A/LT338A LM138/LM338 U W TYPICAL PERFOR A CE CHARACTERISTICS Current Limit Current Limit PEAK CURRENT LIMIT DC CURRENT LIMIT TCASE = 25C 14 14 12 12 8 PRELOAD = 1A 4 10 PRELOAD = 5A 8 6 4 2 0 20 10 30 INPUT-OUTPUT DIFFERENTIAL (V) 40 OUTPUT CURRENT (A) PRELOAD = 5A 0 0 0.1 1 10 VIN - VOUT = 30V 1 10 100 TIME (ms) 138A/338A G12 138A/338A G11 Load Transient Response OUTPUT VOLTAGE DEVIATION (V) 3 CL = 1F CL = 10F - 0.5 COUT = 0 CADJ = 0 -1.0 1.0 0.5 0 10 20 TIME (s) 40 30 2 1 CL = 1F CADJ = 10F CL = 0 CADJ = 0 0 -1 VIN = 15V VOUT = 10V TCASE = 25C PRELOAD = 100mA -2 -3 -1.5 INPUT VOLTAGE CHANGE (V) VIN - VOUT = 20V 4 TIME (ms) 0 0 VIN - VOUT = 15V 6 0 0.1 100 LOAD CURRENT (A) OUTPUT VOLTAGE DEVIATION (V) 0.5 VOUT = 10V IOUT = 50mA TJ = 25C VIN - VOUT = 10V 8 2 Line Transient Response 1.0 10 VIN = 10V VOUT = 5V TCASE = 25C 138A/338A G10 1.5 PRELOAD CURRENT = 0 TCASE = 25C PRELOAD = 0A PRELOAD = 0A 12 OUTPUT CURRENT (A) OUTPUT CURRENT (A) 16 Current Limit 6 4 2 0 0 10 20 TIME (s) 138A/338A G13 30 40 138A/338A G14 U W U U APPLICATIONS INFORMATION General The LT138A develops a 1.25V reference voltage between the output and the adjustable terminal (see Figure 1). By placing a resistor, R1, 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 IADJ is very small and constant when compared with the current through R1, 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 accuracy of VREF. 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. LT338A VIN VIN VOUT ADJ + VOUT VREF R1 IADJ 50A R2 ( ) 138A/338A F01 VOUT = VREF 1 + R2 + IADJ * R2 R1 Figure 1. Basic Adjustable Regulator 5 LT138A/LT338A LM138/LM338 U U W U APPLICATIONS INFORMATION For example, using 2% resistors and 4% tolerance for VREF, calculations will show that the expected range of a 5V regulator design would be 4.66V VOUT 5.36V 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 adjustable regulators over existing devices is the tightened initial tolerance of VREF. 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. Table 1. 0.5% and 1% Standard Resistance Values 1.00 1.02 1.05 1.07 1.10 1.13 1.15 1.18 1.21 1.24 1.27 1.30 1.33 1.37 1.40 1.43 1.47 1.50 1.54 1.58 1.62 1.65 1.69 1.74 1.78 1.82 1.87 1.91 1.96 2.00 2.05 2.10 2.15 2.21 2.26 2.32 2.37 2.43 2.49 2.55 2.61 2.67 2.74 2.80 2.87 2.94 3.01 3.09 3.16 3.24 3.32 3.40 3.48 3.57 3.65 3.74 3.83 3.92 4.02 4.12 4.22 4.32 4.42 4.53 4.64 4.75 4.87 4.99 5.11 5.23 5.36 5.49 5.62 5.76 5.90 6.04 6.19 6.34 6.49 6.65 6.81 6.98 7.15 7.32 7.50 7.68 7.87 8.06 8.25 8.45 8.66 8.87 9.09 9.31 9.53 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 6 (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 possibility 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/LT338A 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 capacitor to improve ripple rejection. If a very 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. D1 1N4002 LT338A VIN VOUT VIN ADJ VOUT R1 CADJ 10F NOT NEEDED + R2 COUT 100F 138A/338A F02 Figure 2 Load Regulation Because the LT138A is a three-terminal device, it is not possible to provide true remote load sensing. Load regulation 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 LT138A/LT338A LM138/LM338 U W U U APPLICATIONS INFORMATION negative side of the load. Although it may not be immediately obvious, best load regulation is obtained when the top of the resistor 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: LT338A VOUT VIN VIN RP PARASITIC LINE RESISTANCE ADJ CONNECT R1 TO CASE R1 RL R2 R2 + R1 RP , RP = Parasitic Line Re sistance R1 CONNECT R2 TO LOAD 138A/338A F03 Connected as shown, RP is not multiplied by the divider ratio. RP 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. Figure 3. Connections for Best Load Regulation U TYPICAL APPLICATIONS Improving Ripple Rejection LT338A VIN VIN + VOUT 1F 5V R1 121 1% ADJ R2 365 1% + CL* 10F 138A/338A TA03 *C1 IMPROVES RIPPLE REJECTION, XC SHOULD BE SMALL COMPARED TO R2 1.2V to 25V Adjustable Regulator LT338A R1 240 ADJ + VOUT VOUT VIN VIN C1* 1F R2 5k + C2** 1F 138A/338A TA04 *NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS **OPTIONAL, IMPROVES TRANSIENT RESPONSE ( ) VOUT = 1.25V 1 + R2 R1 7 LT138A/LT338A LM138/LM338 U TYPICAL APPLICATIONS 5V Regulator with Shutdown LT338A VIN VIN VOUT + 5V 121 1% ADJ 1F 1k TTL 2N3904 365 1% 1k 138A/338A TA05 Temperature Compensated Lead Acid Battery Charger LT338A 3A VIN VOUT 243 1% ADJ 10k 50 12V 2N3906 2k 50k 138A/338A TA07 Remote Sensing RP (MAX DROP 300mV) LT338A VIN VOUT 5V VOUT VIN ADJ VIN - 2 + 3 7 121 6 LM301A 1 8 365 100pF 4 RL 1k 5F + 25 25 RETURN RETURN 8 138A/338A TA06 160k Q1 Q3 30k 180 Q5 Q4 Q7 130 4k Q6 310 Q8 4.1k Q11 12.4k Q9 190 4.1k Q10 10 Q12 Q13 Q1 50 Q14 5.1k Q16 3k Q15 + 5.6k C2 30pF + C1 30pF 20k Q17 Q18 ADJ 12k Q19 2.4k Q20 1.6k Q21 Q22 6.7k Q23 16k Q25 C3 5pF Q24 400 12k 120 Q26 200 300 160k Q27 VOUT 160 D2 18k D1 138A/338A SS 0.01 3 Q28 SCHE ATIC DIAGRA Q2 310 VIN LT138A/LT338A LM138/LM338 W W LT138A/LT338A 9 LT138A/LT338A LM138/LM338 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. K Package 2-Lead TO-3 Metal Can (LTC DWG # 05-08-1310) 0.760 - 0.775 (19.30 - 19.69) 0.320 - 0.350 (8.13 - 8.89) 0.060 - 0.135 (1.524 - 3.429) 0.420 - 0.480 (10.67 - 12.19) 0.038 - 0.043 (0.965 - 1.09) 1.177 - 1.197 (29.90 - 30.40) 0.655 - 0.675 (16.64 - 17.15) 0.210 - 0.220 (5.33 - 5.59) 0.167 - 0.177 (4.24 - 4.49) R 0.425 - 0.435 (10.80 - 11.05) 0.067 - 0.077 (1.70 - 1.96) 10 0.151 - 0.161 (3.86 - 4.09) DIA, 2PLCS 0.490 - 0.510 (12.45 - 12.95) R K2 (TO-3) 1098 LT138A/LT338A LM138/LM338 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. P Package 3-Lead Plastic TO-3P (Similar to TO-247) (LTC DWG # 05-08-1450) 0.560 (14.224) 0.325 (8.255) 0.275 (6.985) 0.580 (14.732) 0.700 (17.780) 0.830 - 0.870 (21.08 - 22.10) 0.580 - 0.6OO (14.73 - 15.24) 0.098 (2.489) 0.124 (3.149) 0.187 - 0.207 (4.75 - 5.26) 0.620 - 0.64O (15.75 - 16.26) MOUNTING HOLE 18 - 22 0.115 - 0.145 (2.92 - 3.68) DIA 0.060 - 0.080 (1.52 - 2.03) 0.170 - 0.2OO (4.32 - 5.08) EJECTOR PIN MARKS 0.105 - 0.125 (2.67 - 3.18) DIA 3 - 7 0.170 (4.32) MAX 0.780 - 0.800 (19.81 - 20.32) BOTTOM VIEW OF TO-3P HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK 0.042 - 0.052 (1.07 - 1.32) 0.074 - 0.084 (1.88 - 2.13) 0.215 (5.46) BSC 0.113 - 0.123 (2.87 - 3.12) 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 0.087 - 0.102 (2.21 - 2.59) 0.020 - 0.040 (0.51 - 1.02) P3 0996 11 LT138A/LT338A LM138/LM338 U TYPICAL APPLICATIONS Lamp Flasher Automatic Light Control LT338A 15V VIN + ADJ 1F LT338A VOUT VIN + 12k 10F 12k 10F 1.2k 12V + OFF VOUT ADJ 10F + 1k 2N3904 138A/338A TA09 12k 138A/338A TA08 Protected High Current Lamp Driver 15V 12V 5A LT338A VIN VOUT ADJ TTL OR CMOS 10k 138A/338A TA10 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1084 5A Low Dropout Operates to 30V Input 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 LT1585/LT1587 7A/4.6A/3A Low Dropout Fast Transient Response Regulator For 1.2V to 3.3V Outputs from 5V 12 Linear Technology Corporation 138afa LT/LT 1199 2K REV A * PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 FAX: (408) 434-0507 www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1991