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LT138A/LT338A LM138/LM338 5A Positive Adjustable Voltage Regulator
FEATURES
s s s s s
DESCRIPTIO
Guaranteed 1% Initial Tolerance Guaranteed 0.3% Load Regulation Guaranteed 5A Output Current 100% Thermal Limit Burn-In 12A Transient Output Current
APPLICATIO S
s s s s
High Power Linear Regulator Battery Chargers Power Driver Constant-Current Regulator
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. 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.
TYPICAL APPLICATIO
Parallel Regulators for Higher Current*
12
LT338A VIN VIN ADJ VOUT
0.01**
OUTPUT VOLTAGE ERROR (%)
5V 8A
11 10 9 8 7 6 5 4 3 2 1 0 1% RESISTORS 2% RESISTORS LT338A 2% RESISTORS 1% RESISTORS LM338 LM338 LT338A
LT350A VIN ADJ VOUT
0.016** 121 1% 365 1%
138/338 TA01
1
*THIS CIRCUIT WILL NOT WORK WITH LM VERSION DEVICES **CURRENT SHARING RESISTORS DEGRADE REGULATION TO 1%
U
Output Voltage Error
10 OUTPUT VOLTAGE (V) 100
138A/338A TA02
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1
LT138A/LT338A LM138/LM338 ABSOLUTE AXI U RATI GS
Power Dissipation .............................. Internally Limited Input-to-Output Voltage Differential ........................ 35V Operating Junction Temperature Range LT138A/LM138 ............................... - 55C to 150C LT338A/LM338 ................................... 0C to 125C
PRECONDITIONI G
100% Thermal Limit Burn-In
PACKAGE/ORDER I FOR ATIO
BOTTOM VIEW VIN 2 CASE IS OUTPUT 1 ADJ 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)
ORDER PART NUMBER LT138AK LT338AK LM138K LM338K
FRONT VIEW 3 2 1 P PACKAGE 3-LEAD PLASTIC TO-3P VOUT VIN ADJ
TJMAX = 125C, JA = 45C/ W
OBSOLETE PACKAGE
Consider the P Package for Alternate Source
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 2)
SYMBOL VREF PARAMETER Reference Voltage CONDITIONS IOUT = 10mA, TJ = 25C 3V (VIN - VOUT) 35V, 10mA IOUT 5A, P 50W VOUT VIN VOUT IOUT Line Regulation Load Regulation 3V (VIN - VOUT) 35V, (Note 3)
q q
ELECTRICAL CHARACTERISTICS
MIN 1.238 1.225
LT138A TYP MAX 1.250 1.250 0.005 0.02 5 0.1 1.262 1.270 0.01 0.04 15 0.3 30 0.6 0.01
10mA IOUT 5A, (Note 3) VOUT 5V VOUT 5V VOUT 5V VOUT 5V
q q
20 0.3 0.002
Thermal Regulation Ripple Rejection
20ms Pulse VOUT = 10V, f = 120Hz CADJ = 0F CADJ = 10F 10mA IOUT 5A, 3V (VIN - VOUT) 35V (VIN - VOUT) = 35V
q q q q q
60
60 75 45 0.2 3.5 100 5 5
IADJ IADJ
Adjust Pin Current Adjust Pin Current Change Minimum Load Current
2
UU
U
U
U
W
WW
U
W
(Note 1)
Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LM338P
MIN 1.19
LM138 TYP 1.24 0.005 0.02 5 0.1 20 0.3 0.002 60 75 45 0.2 3.5
MAX 1.29 0.01 0.04 15 0.3 30 0.6 0.01
UNITS V V %/V %/V mV % mV % %/W dB dB
60
100 5 5
A A mA
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LT138A/LT338A LM138/LM338
ELECTRICAL CHARACTERISTICS
SYMBOL ISC PARAMETER Current Limit CONDITIONS (VIN - VOUT) 10V DC 0.5ms Peak (VIN - VOUT) = 30V, TJ = 25C VOUT Temp VOUT Time en JC Temperature Stability Long-Term Stability TA = 125C, 1000 Hours
q q q
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 2)
MIN 5 6 LT138A TYP MAX 8 12 1 1 0.3 0.001 1 2 2 1 MIN 5 6 LM138 TYP 8 12 1 1 0.3 0.003 1 1 MAX UNITS A A A % % % C/W
RMS Output Noise (% of VOUT) 10Hz f 10kHz Thermal Resistance Junction-to-Case K Package
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 2)
SYMBOL VREF PARAMETER Reference Voltage CONDITIONS IOUT = 10mA 3V (VIN - VOUT) 35V, 10mA IOUT 5A, P 50W VOUT VIN VOUT IOUT Line Regulation Load Regulation 3V (VIN - VOUT) 35V, (Note 3)
q q
MIN 1.238 1.225
LT338A TYP MAX 1.250 1.250 0.005 0.02 5 0.1 1.262 1.270 0.01 0.04 15 0.3 30 0.6 0.02
MIN 1.19
LM338 TYP 1.24 0.005 0.02 5 0.1 20 0.3 0.002 60 75 45 0.2 3.5
MAX 1.29 0.03 0.06 25 0.5 50 1 0.02
UNITS V V %/V %/V mV % mV % %/W dB dB
10mA IOUT 5A, (Note 3) VOUT 5V VOUT 5V VOUT 5V VOUT 5V
q q
20 0.3 0.002
Thermal Regulation Ripple Rejection
20ms Pulse VOUT = 10V, f = 120Hz CADJ = 0F CADJ = 10F 10mA IOUT 5A, 3V (VIN - VOUT) 35V (VIN - VOUT) = 35V (VIN - VOUT) 10V DC 0.5ms Peak (VIN - VOUT) = 30V, TJ = 25C
q q q q q q q
60
60 75 45 0.2 3.5 100 5 10
60
IADJ IADJ
Adjust Pin Current Adjust Pin Current Change Minimum Load Current
100 5 10
A A mA A A A %
ISC
Current Limit
5 6
8 12 1 2 2 1 1 0.3 0.001 1
5 6
8 12 1 1 0.3 0.003 1 1
VOUT Temp VOUT Time en JC
Temperature Stability Long-Term Stability RMS Output Noise (% of VOUT) Thermal Resistance Junction-to-Case TA = 125C, 1000 Hours 10Hz f 10kHz K Package
q
% % C/W
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.
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.
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LT138A/LT338A LM138/LM338 TYPICAL PERFOR A CE CHARACTERISTICS
Load Regulation
0.2 VIN = 15V VOUT = 10V PRELOAD = 50mA IOUT = 3A IOUT = 5A 4
OUTPUT VOLTAGE DEVIATION (%)
ADJUSTMENT CURRENT (A)
0.1 0 - 0.1 - 0.2 - 0.3
INPUT-OUTPUT DIFFERENTIAL (V)
- 0.4 -75 - 50 - 25
0 25 50 75 100 125 150 TEMPERATURE (C)
138/338 G01
Temperature Stability
1.270
10
OUTPUT IMPEDANCE ()
1.260
QUIESCENT CURRENT (mA)
REFERENCE VOLTAGE (V)
1.250
1.240
1.230 -50 -25
0
25 50 75 100 125 150 TEMPERATURE (C)
138A/338A G04
Ripple Rejection
100 CADJ = 10F 80
RIPPLE REJECTION (dB)
RIPPLE REJECTION (dB)
CADJ = 0F 60
60 CADJ = 0F 40
RIPPLE REJECTION (dB)
40 VIN - VOUT = 5V IOUT = 500mA f = 120Hz TJ = 25C 0 5 20 15 10 25 OUTPUT VOLTAGE (V) 30 35
20
0
4
UW
138A/338A G07
Dropout Voltage
VOUT = 100mV 65 60 55 50 45 40 35 1 -75 - 50 - 25
Adjustment Current
3 IOUT = 5A IOUT = 3A 2 IOUT = 1A
0 25 50 75 100 125 150 TEMPERATURE (C)
138/338 G02
30 -75
-25
25 75 TEMPERATURE (C)
125
138A/338A G03
Output Impedance
VIN = 15V VOUT = 10V IOUT = 500mA CADJ = COUT = 0F 5
Minimum Operating Current
1
4 TJ = 150C TJ = 25C 3 TJ = - 55C
0.1
0.01 CADJ = COUT = 10F
2
0.001
1
0.0001
0 10 100 10k 1k FREQUENCY (Hz) 100k 1M 0 25 30 35 5 10 15 20 INPUT-OUTPUT DIFFERENTIAL (V) 40
138/338 G05
138A/338A G06
Ripple Rejection
100
80
Ripple Rejection
CADJ = 10F
80
CADJ = 10F
70 CADJ = 0F 60
50
20
0
VIN = 15V VOUT = 10V IOUT = 0.2A 10 100 10k 1k FREQUENCY (Hz) 100k 1M
40
VIN = 15V VOUT = 10V f = 120Hz TCASE = 25C 0.1 1 OUTPUT CURRENT (A) 10
138/338 G09
138A/338A G08
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LT138A/LT338A LM138/LM338 TYPICAL PERFOR A CE CHARACTERISTICS
Current Limit
16 PEAK CURRENT LIMIT DC CURRENT LIMIT TCASE = 25C
OUTPUT CURRENT (A)
14 12 PRELOAD = 0A
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
12
PRELOAD = 0A
PRELOAD = 5A 8
PRELOAD = 1A 4
0
0
20 10 30 INPUT-OUTPUT DIFFERENTIAL (V)
Line Transient Response
1.5
OUTPUT VOLTAGE DEVIATION (V)
OUTPUT VOLTAGE DEVIATION (V)
1.0 0.5 0 - 0.5 -1.0 -1.5
VOUT = 10V IOUT = 50mA TJ = 25C
LOAD CURRENT (A)
INPUT VOLTAGE CHANGE (V)
1.0 0.5 0 0 10 20 TIME (s) 30 40
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 ADJ VOUT VREF R1 VOUT
U
W
UW
138A/338A G10
Current Limit
14 12 10
Current Limit
PRELOAD CURRENT = 0 TCASE = 25C
10 PRELOAD = 5A 8 6 4 2 VIN = 10V VOUT = 5V TCASE = 25C 1 TIME (ms)
138A/338A G11
VIN - VOUT = 10V 8 6 4 2 0 0.1 VIN - VOUT = 15V VIN - VOUT = 20V VIN - VOUT = 30V
40
0 0.1
10
100
1 TIME (ms)
10
100
138A/338A G12
Load Transient Response
3 2 1 0 -1 -2 -3 6 4 2 0 0 10 20 TIME (s) 30 40 VIN = 15V VOUT = 10V TCASE = 25C PRELOAD = 100mA CL = 1F CADJ = 10F CL = 0 CADJ = 0
CL = 1F CL = 10F
COUT = 0 CADJ = 0
138A/338A G13
138A/338A G14
U
U
+
IADJ 50A R2 VOUT = VREF 1 + R2 + IADJ * R2 R1
()
138A/338A F01
Figure 1. Basic Adjustable Regulator
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LT138A/LT338A LM138/LM338
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
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W
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U
(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 VIN ADJ VOUT R1 NOT NEEDED VOUT
CADJ 10F
+
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
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LT138A/LT338A LM138/LM338
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 VIN VIN ADJ VOUT CONNECT R1 TO CASE R1 RL R2 CONNECT R2 TO LOAD
138A/338A F03
R2 + R1 RP , RP = Parasitic Line Re sistance R1
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.
TYPICAL APPLICATIONS
Improving Ripple Rejection
LT338A VIN
+
1F
*C1 IMPROVES RIPPLE REJECTION, XC SHOULD BE SMALL COMPARED TO R2
1.2V to 25V Adjustable Regulator
LT338A VIN VIN ADJ VOUT R1 240 R2 5k VOUT
+
*NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS **OPTIONAL, IMPROVES TRANSIENT RESPONSE
VOUT = 1.25V 1 + R2 R1
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W
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RP PARASITIC LINE RESISTANCE
Figure 3. Connections for Best Load Regulation
VIN ADJ
VOUT
R1 121 1% R2 365 1%
5V
+
CL* 10F
138A/338A TA03
C1* 1F
+
C2** 1F
138A/338A TA04
()
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LT138A/LT338A LM138/LM338
TYPICAL APPLICATIONS
5V Regulator with Shutdown
LT338A VIN VIN VOUT ADJ 1F 1k TTL 1k 2N3904 365 1% 121 1% 5V
LT338A VIN VIN ADJ VIN 25 121 6 1 8 365 100pF VOUT
LM301A 3
+
RETURN
8
-
+
U
+
138A/338A TA05
Temperature Compensated Lead Acid Battery Charger
LT338A VIN ADJ VOUT 243 1% 10k 50 2N3906 2k 50k
138A/338A TA07
3A
12V
Remote Sensing
RP (MAX DROP 300mV)
VOUT 5V
7
2 RL
1k 5F
4
25 RETURN
138A/338A TA06
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SCHE ATIC DIAGRA W W
VIN 310 300 Q1 Q26 200 Q6 Q9 Q15 Q14 1.6k Q21 C3 5pF Q18 Q10 Q16 Q8 Q11 Q12 Q13 C1 30pF Q17 2.4k 3 4.1k 10 12k 0.01 VOUT ADJ
138A/338A SS
310
190
50
5.6k
20k
Q23
Q24
Q27 120 Q28 D1
Q2 Q19 6.7k 12k
Q4
LT138A/LT338A
30k 4k 3k 12.4k Q22 16k Q25 Q20 130
Q5
400
160k
18k
D2
+ +
Q1 4.1k 5.1k C2 30pF
160
Q3
Q7
160k
180
LT138A/LT338A LM138/LM338
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LT138A/LT338A LM138/LM338
PACKAGE DESCRIPTION
K Package 2-Lead TO-3 Metal Can
(Reference LTC DWG # 05-08-1310)
0.320 - 0.350 (8.13 - 8.89)
0.420 - 0.480 (10.67 - 12.19)
0.425 - 0.435 (10.80 - 11.05) 0.067 - 0.077 (1.70 - 1.96)
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0.760 - 0.775 (19.30 - 19.69) 0.060 - 0.135 (1.524 - 3.429)
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) 0.151 - 0.161 (3.86 - 4.09) DIA, 2PLCS 0.167 - 0.177 (4.24 - 4.49) R 0.490 - 0.510 (12.45 - 12.95) R
K2 (TO-3) 1098
OBSOLETE PACKAGE
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LT138A/LT338A LM138/LM338
PACKAGE DESCRIPTION
P Package 3-Lead Plastic TO-3P (Similar to TO-247)
(Reference 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)
0.780 - 0.800 (19.81 - 20.32)
BOTTOM VIEW OF TO-3P HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK
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.
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0.620 - 0.64O (15.75 - 16.26)
0.187 - 0.207 (4.75 - 5.26) 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
0.042 - 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)
0.087 - 0.102 (2.21 - 2.59) 0.020 - 0.040 (0.51 - 1.02)
P3 0996
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LT138A/LT338A LM138/LM338
TYPICAL APPLICATIONS
Lamp Flasher
LT338A 15V
+
1F
VIN ADJ
VOUT 10F
OFF
12k
1k 2N3904
12k
12k
RELATED PARTS
PART NUMBER LT1083/LT1084/LT1085 LT1580 LT1581 LT1584/LT1585/LT1587 LT1764 DESCRIPTION 3A/5A/7.5A Low Dropout Regulators 7A Fast Transient Response Regulator with 0.7V Dropout 10A Fast Transient Response Regulator 7A/4.6A/3A Low Dropout Fast Transient Response Regulator 3A Fast Transient Response Regulator COMMENTS Fixed Outputs, VIN Up to 30V For 3.3V to 2.xxV Applications For 3.3V to 2.xxV Applications For 1.2V to 3.3V Outputs from 5V Dropout Voltage 340mV, Low Noise: 40VRMS
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
U
Automatic Light Control
LT338A VIN ADJ VOUT 1.2k
10F
10F
+ + +
TTL OR CMOS
12V
138A/338A TA09
138A/338A TA08
Protected High Current Lamp Driver
15V LT338A VOUT ADJ VIN 12V 5A
10k
138A/338A TA10
138afb LT/CPI 1101 1.5K REV B * PRINTED IN THE USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 1991

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