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138A/338A Rev A copy
LT138A/LT338A
LM138/LM338
5A Positive Adjustable
Voltage Regulator
FEATURES
DESCRIPTIO
n
Guaranteed 1% Initial Tolerance
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 excel-
lent 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 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.
n
Guaranteed 0.3% Load Regulation
Guaranteed 5A Output Current
n
100% Thermal Limit Burn-In
n
n
12A Transient Output Current
APPLICATIO U
n
High Power Linear Regulator
n
Battery Chargers
n
Power Driver
n
Constant-Current Regulator
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
Parallel Regulators for Higher Current*
Output Voltage Error
LT338A
0.01
½
**
12
11
5V
8A
V IN
V IN
V OUT
10
ADJ
9
2% RESISTORS
8
LM338
7
1% RESISTORS
6
LM338
LT338A
LT350A
0.016
½
**
V IN
V OUT
5
ADJ
121 ½
1%
4
2% RESISTORS
3
LT338A
2
1% RESISTORS
365
½
1
1%
0
1
10
100
138/338 TA01
OUTPUT VOLTAGE (V)
*
**
THIS CIRCUIT WILL NOT WORK WITH LM VERSION DEVICES
CURRENT SHARING RESISTORS DEGRADE REGULATION TO 1%
138A/338A TA02
1
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LT138A/LT338A
LM138/LM338
A
BSOLUTEI
A
U
R
I S
G
(Note 1)
Power Dissipation .............................. Internally Limited
Input-to-Output Voltage Differential ........................ 35V
Operating Junction Temperature Range
LT138A/LM138 ............................... – 55
Storage Temperature Range ................ – 65
°
C to 150
°
C
Lead Temperature (Soldering, 10 sec) ................. 300
°
C
°
C to 150
°
C
PRECO N DITIO N I G
LT338A/LM338 ................................... 0
°
C to 125
°
C
100% Thermal Limit Burn-In
PACKAGE / ORDER I FOR ATIO
BOTTOM VIEW
ORDER
PART NUMBER
ORDER
PART NUMBER
V IN
FRONT VIEW
2
LT138AK
LT338AK
LM138K
LM338K
3
V OUT
V IN
ADJ
LM338P
CASE
IS OUTPUT
2
1
1
ADJ
P PACKAGE
3-LEAD PLASTIC TO-3P
T JMAX = 125 ° C, q JA = 45 ° C/ W
K PACKAGE
2-LEAD TO-3 METAL CAN
C/ W (LT138A/LT138)
T JMAX = 125 ° C, q JA = 35 ° C/ W, q JC = 1 ° C/ W (LT338A/LT338)
°
C,
q JA = 35
C/ W,
q JC = 1
°
Consult factory for Industrial grade parts.
ELECTRICAL CHARACTERISTICS
The l denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T A = 25
°
C. (Note 2)
LT138A
LM138
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
V REF
Reference Voltage
I OUT = 10mA, T J = 25
°
C
1.238 1.250 1.262
V
3V £ (V IN – V OUT ) £ 35V,
l
1.225 1.250 1.270
1.19
1.24
1.29
V
10mA £ I OUT £ 5A, P £ 50W
D V OUT
Line Regulation
3V £ (V IN – V OUT ) £ 35V, (Note 3)
0.005 0.01
0.005 0.01
%/V
D V IN
l
0.02
0.04
0.02
0.04
%/V
D V OUT
Load Regulation
10mA £ I OUT £ 5A, (Note 3)
D I OUT
V OUT £ 5V
5
15
5
15
mV
V OUT ³ 5V
0.1
0.3
0.1
0.3
%
V OUT £ 5V
l
20
30
20
30
mV
V OUT ³ 5V
l
0.3
0.6
0.3
0.6
%
Thermal Regulation
20ms Pulse
0.002 0.01
0.002 0.01
%/W
Ripple Rejection
V OUT = 10V, f = 120Hz
C ADJ = 0
m
F
l
60
60
dB
C ADJ = 10
m
F
l
60
75
60
75
dB
I ADJ
Adjust Pin Current
l
45
100
45
100
m
A
D I ADJ
Adjust Pin Current Change
10mA £ I OUT £ 5A,
l
0.2
5
0.2
5
m A
3V £ (V IN – V OUT ) £ 35V
Minimum Load Current
(V IN – V OUT ) = 35V
l
3.5
5
3.5
5
mA
I SC
Current Limit
(V IN – V OUT ) £ 10V
DC
l
5
8
5
8
A
0.5ms Peak
l
6
12
6
12
A
(V IN – V OUT ) = 30V, T J = 25 ° C
1
2
1
A
2
T JMAX = 150
°
208372839.008.png 208372839.009.png 208372839.010.png 208372839.011.png 208372839.012.png 208372839.013.png 208372839.014.png 208372839.015.png 208372839.016.png
LT138A/LT338A
LM138/LM338
ELECTRICAL CHARACTERISTICS
The l denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T A = 25
°
C. (Note 2)
LT138A
LM138
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
D V OUT
Temperature Stability
l
1
2
1
%
D Temp
D V OUT
Long-Term Stability
T A = 125 ° C, 1000 Hours
0.3
1
0.3
1
%
D Time
e n
RMS Output Noise (% of V OUT ) 10Hz £ f £ 10kHz
0.001
0.003
%
q JC
Thermal Resistance
K Package
1
1
°
C/W
Junction-to-Case
The l denotes specifications which apply over the full operating temperature range,
otherwise specifications are at T A = 25
°
C. (Note 2)
LT338A
LM338
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNITS
V REF
Reference Voltage
I OUT = 10mA
1.238 1.250 1.262
V
3V
£
(V IN – V OUT )
£
35V,
l
1.225 1.250 1.270
1.19
1.24
1.29
V
10mA
I OUT
£
5A, P
£
50W
D V OUT
Line Regulation
3V £ (V IN – V OUT ) £ 35V, (Note 3)
0.005 0.01
0.005 0.03
%/V
D V IN
l
0.02
0.04
0.02
0.06
%/V
D V OUT
Load Regulation
10mA £ I OUT £ 5A, (Note 3)
D I OUT
V OUT £ 5V
5
15
5
25
mV
V OUT ³ 5V
0.1
0.3
0.1
0.5
%
V OUT £ 5V
l
20
30
20
50
mV
V OUT ³ 5V
l
0.3
0.6
0.3
1
%
Thermal Regulation
20ms Pulse
0.002 0.02
0.002 0.02
%/W
Ripple Rejection
V OUT = 10V, f = 120Hz
C ADJ = 0
m
F
l
60
60
dB
C ADJ = 10
m
F
l
60
75
60
75
dB
I ADJ
Adjust Pin Current
l
45
100
45
100
m
A
D I ADJ
Adjust Pin Current Change
10mA £ I OUT £ 5A,
l
0.2
5
0.2
5
m A
3V £ (V IN – V OUT ) £ 35V
Minimum Load Current
(V IN – V OUT ) = 35V
l
3.5
10
3.5
10
mA
I SC
Current Limit
(V IN – V OUT ) £ 10V
DC
l
5
8
5
8
A
0.5ms Peak
l
6
12
6
12
A
(V IN – V OUT ) = 30V, T J = 25 ° C
1
2
1
A
D
V OUT
Temperature Stability
l
1
2
1
%
D
Temp
D
V OUT
Long-Term Stability
T A = 125
°
C, 1000 Hours
0.3
1
0.3
1
%
Time
e n
RMS Output Noise (% of V OUT ) 10Hz
£
f
£
10kHz
0.001
0.003
%
q JC
Thermal Resistance
K Package
1
1
° C/W
Junction-to-Case
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:
V IN – 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.
3
£
D
208372839.017.png
LT138A/LT338A
LM138/LM338
TYPICAL PERFOR A CE CHARACTERISTICS
Load Regulation
Dropout Voltage
Adjustment Current
0.2
V IN = 15V
V OUT = 10V
PRELOAD = 50mA
4
Æ
V OUT = 100mV
65
0.1
60
0
I OUT = 3A
3
55
I OUT = 5A
50
I OUT = 5A
– 0.1
I OUT = 3A
45
– 0.2
2
40
I OUT = 1A
– 0.3
35
– 0.4
–75
–50
–25
0
25 50
75 100 125
150
1
–75
–50
–25
0
25 50
75 100 125
150
30
–75
–25
25
75
125
TEMPERATURE (
°
C)
TEMPERATURE ( ° C)
TEMPERATURE ( ° C)
138/338 G01
138/338 G02
138A/338A G03
Temperature Stability
Output Impedance
Minimum Operating Current
1.270
10
5
V IN = 15V
V OUT = 10V
I OUT = 500mA
1
4
1.260
T J = 150
°
C
C ADJ = C OUT = 0
µ
F
T J = 25 ° C
0.1
3
1.250
0.01
2
T J = – 55
°
1.240
C ADJ = C OUT = 10 µ F
0.001
1
1.230
0.0001
0
–50
–25 0
25 50
75 100 125 150
10
100
1k
10k
100k
1M
0
50
15
20
25
30 35
40
TEMPERATURE (
°
C)
FREQUENCY (Hz)
INPUT-OUTPUT DIFFERENTIAL (V)
138A/338A G04
138/338 G05
138A/338A G06
Ripple Rejection
Ripple Rejection
Ripple Rejection
100
100
80
C ADJ = 10 µ F
C ADJ = 10 µ F
80
80
C ADJ = 10
µ
F
70
C ADJ = 0 µ F
60
60
C ADJ = 0 µ F
C ADJ = 0 µ F
60
40
40
V IN – V OUT = 5V
I OUT = 500mA
f = 120Hz
T J = 25
50
V IN = 15V
V OUT = 10V
f = 120Hz
T CASE = 25
20
20
V IN = 15V
V OUT = 10V
I OUT = 0.2A
°
°
C
0
40
0
0
5
10
15
20
25
30
35
10
100
1k
10k
100k
1M
0.1
1
10
OUTPUT VOLTAGE (V)
FREQUENCY (Hz)
OUTPUT CURRENT (A)
138A/338A G07
138A/338A G08
138/338 G09
4
C
C
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LT138A/LT338A
LM138/LM338
TYPICAL PERFOR A CE CHARACTERISTICS
Current Limit
Current Limit
Current Limit
16
P EAK CURRENT LIMIT
DC CURRENT LIMIT
T CASE = 25
14
14
PRELOAD CURRENT = 0
T CASE = 25
°
C
°
12
12
PRELOAD = 0A
12
PRELOAD = 0A
10
10
PRELOAD = 5A
V IN – V OUT = 10V
P R ELOAD = 5A
8
8
8
V IN – V OUT = 15V
6
6
PRELOAD = 1A
4
4
V IN – V OUT = 20V
4
2
V IN = 10V
V OUT = 5V
T CASE = 25
2
V IN – V OUT = 30V
°
C
0
0
0
0
10
20
30
40
0.1
1
10
100
0.1
1
10
100
INPUT-OUTPUT DIFFERENTIAL (V)
TIME (ms)
TIME (ms)
138A/338A G10
138A/338A G11
138A/338A G12
Line Transient Response
Load Transient Response
1.5
V OUT = 10V
I OUT = 50mA
T J = 25 ° C
3
1.0
2
C L = 1 µ F
C ADJ = 10 µ F
C L = 0
C ADJ = 0
0.5
C L = 1 µ F
C L = 10 µ F
1
0
0
– 0.5
–1
V IN = 15V
V OUT = 10V
T CASE = 25
C OUT = 0
C ADJ = 0
–2
–1.0
–3
C
PRELOAD = 100mA
°
–1.5
6
1.0
4
0.5
2
0
0
0
10
20
30
40
0
10
20
30
40
TIME (
µ
TIME (
µ
s)
138A/338A G13
138A/338A G14
APPLICATIO N S I N FOR M ATIO N
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 con-
stant 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 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 V REF . Earlier adjustable regulators had a reference
5%
supply tolerance required in many logic and analog sys-
tems. Further, even 1% resistors can drift 0.01%/
±
4% which is dangerously close to the
±
C, add-
ing additional error to the output voltage tolerance.
°
LT338A
V IN
V IN
V OUT
V OUT
+
ADJ
V REF
R1
I ADJ
50 µ A
R2
( )
138A/338A F01
R2
R1
V OUT = V REF
1 +
+ I ADJ • R2
Figure 1. Basic Adjustable Regulator
5
C
s)
tolerance of
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