ST LM138, LM238, LM338 User Manual
Three-terminal 5 A adjustable voltage regulators
Features
■ Guaranteed 7 A peak output current
■ Guaranteed 5 A output current
■ Adjustable output down to 1.2 V
■ Line regulation typically 0.005 %/V
■ Load regulation typically 0.1 %
■ Guaranteed thermal regulation
■ Current limit constant with temperature
■ Standard 3-lead transistor package
Description
The LM138, LM238, LM338 are adjustable 3terminal positive voltage regulators capable of
supplying in excess of 5 A over a 1.2 V to 32 V
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 current limiting. The current limit circuitry
allows peak currents of up to 12 A to be drawn
from the regulator for short periods of time. This
allows the LM138 to be used with heavy transient
loads and speeds start-up under full-load
conditions. Under sustained loading conditions,
the current limit decreases to a safe value
protecting the regulator. Also included on the chip
are thermal overload protection and safe area
protection for the power transistor. Overload
LM138 - LM238 - LM338
TO-3
protection remains functional even if the
adjustment pin is accidentally disconnected.
Normally, no capacitors are needed unless the
device is situated far from the input filter
capacitors in which case an input bypass is
needed. An optional output capacitor can be
added to improve transient response. The
adjustment terminal can be bypassed to
achieve.very high ripple rejection ratios which are
difficult to achieve with standard 3-terminal
regulators.
Besides replacing fixed regulators or discrete
designs, the LM238 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 input
differential is not exceeded.
The LM138, LM238, LM338 are packaged in
standard steel TO-3 transistor package. The
LM138 is rated for operation from - 55 °C to
150 °C, the LM238 from - 25 °C to 150 °C and the
LM338 from 0 °C to 125 °C.
Table 1. Device summary
Part numbers Order codes Temperature range
LM138 LM138K -55 °C to 150 °C
LM238 LM238K -25 °C to 150 °C
LM338 LM338K 0 °C to 125 °C
April 2008 Rev 2 1/23
www.st.com
23
Contents LM138 - LM238 - LM338
Contents
1 Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6 Typical application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7 Application hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1 External capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.2 Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.3 Protection diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2/23
LM138 - LM238 - LM338 Diagram
1 Diagram
Figure 1. Schematic diagram
3/23
Pin configuration LM138 - LM238 - LM338
2 Pin configuration
Figure 2. Pin connections (top view)
TO-3
4/23
LM138 - LM238 - LM338 Maximum ratings
3 Maximum ratings
Table 2. Absolute maximum ratings
Symbol Parameter Value Unit
V
- VOInput-output voltage differential 35
I
T
T
P
D
STG
LEAD
Power dissipation Internally limited
Storage temperature range -65 to 150 °C
Lead temperature (Soldering, 10 seconds) 300 °C
LM138 -55 to 150
V
T
OP
Operating junction temperature range
°CLM238 -25 to 125
LM338 0 to 125
Note: Absolute maximum ratings are those values beyond which damage to the device may occur.
Functional operation under these condition is not implied.
Table 3. Thermal data
Symbol Parameter Value Unit
R
R
thJC
thJA
Thermal resistance junction-case 1.4 °C/W
Thermal resistance junction-ambient 35 °C/W
5/23
Electrical characteristics LM138 - LM238 - LM338
4 Electrical characteristics
Table 4. Electrical characteristics for LM138/LM238
(1)
Symbol Parameter Test conditions Min. Typ. Max. Unit
K
Line regulation
VI
K
Load regulation
VO
(2)
(2)
TA = 25°C, VI - VO = 3 to 35 V 0.005 0.01 %/V
≤ 5 V 5 15 mV
V
TA = 25°C
= 10 mA to 5 A
I
O
O
V
≥ 5 V 0.1 0.3 %
O
Thermal regulation Pulse = 20 ms 0.002 0.01 %/W
I
ΔI
V
K
K
I
O(MIN)
Adjustment pin current 45 100 µA
ADJ
Adjustment pin current
ADJ
change
Reference voltage
REF
Line regulation
K
VI
Load regulation
VO
Temperature stability TJ = T
VT
(2)
(2)
= 10 mA to 5 A, VI - VO = 3 to 35 V 0.2 5 µA
I
L
- VO = 3 to 35 V, IO = 10 mA to 5 A
V
I
P ≤ 50 W
1.19 1.24 1.29 V
VI - VO = 3 to 35 V 0.02 0.04 %/V
V
≤ 5 V 20 30 mV
IO = 10 mA to 5 A
to T
MIN
MAX
O
V
≥ 5 V 0.3 0.6 %
O
1%
Minimum load current VI - VO ≤ 35 V 3.5 5 mA
DC 5 8
I
O(MAX)
V
R
K
1. (T
2. Regulation is measured at constant junction temperature. Changes in output voltage due to heating effects are taken into
Current limit VI - VO ≤ 10 V
- VO = 30 V 1
V
I
RMS output noise (% of
NO
VO)
Ripple rejection ratio
VF
Long term stability TA = 125°C 0.3 1 %
VH
= -55 to 150 °C for LM138, TJ = -25 to 150 °C for LM238, VI - VO = 5 V, IO = 2.5 A. Although power dissipation is
J
internally limited, these specifications apply to power dissipation up to 50 W, unless otherwise specified)
account separately by thermal rejection.
= 25°C, f = 10 Hz to 10 kHz 0.003 %
T
a
V
= 10 V, f = 120 Hz 60
O
= 10 µF 60 75
C
ADJ
A0.5 ms Peak 7 12
dB
6/23
LM138 - LM238 - LM338 Electrical characteristics
Table 5. Electrical characteristics for LM338
(1)
Symbol Parameter Test conditions Min. Typ. Max. Unit
K
Line regulation
VI
K
Load regulation
VO
(2)
(2)
TA = 25°C, VI - VO = 3 to 35 V 0.005 0.03 %/V
≤ 5 V 5 25 mV
V
TA = 25°C
= 10 mA to 5 A
I
O
O
V
≥ 5 V 0.1 0.5 %
O
Thermal regulation Pulse = 20 ms 0.002 0.02 %/W
I
ΔI
V
K
K
I
O(MIN)
Adjustment pin current 45 100 µA
ADJ
Adjustment pin current
ADJ
change
Reference voltage
REF
Line regulation
K
VI
Load regulation
VO
Temperature stability TJ = T
VT
(2)
(2)
= 10 mA to 5 A, VI - VO = 3 to 35 V 0.2 5 µA
I
L
- VO = 3 to 35 V, IO = 10 mA to 5 A
V
I
P ≤ 50 W
1.19 1.24 1.29 V
VI - VO = 3 to 35 V 0.02 0.06 %/V
V
≤ 5 V 20 50 mV
IO = 10 mA to 5 A
to T
MIN
MAX
O
V
≥ 5 V 0.3 1 %
O
1%
Minimum load current VI - VO ≤ 35 V 3.5 10 mA
DC 5 8
I
O(MAX)
V
R
K
1. (TJ = 0 to150 °C, VI - VO = 5 V, IO = 2.5 A. Although power dissipation is internally limited, these specifications apply to
2. Regulation is measured at constant junction temperature. Changes in output voltage due to heating effects are taken into
Current limit VI - VO ≤ 10 V
- VO = 30 V 1
V
I
RMS output noise (% of
NO
VO)
Ripple rejection ratio
VF
Long term stability TA = 125°C 0.3 1 %
VH
power dissipation up to 50 W, unless otherwise specified)
account separately by thermal rejection.
= 25°C, f = 10 Hz to 10 kHz 0.003 %
T
a
V
= 10 V, f = 120 Hz 60
O
= 10 µF 60 75
C
ADJ
A0.5 ms Peak 7 12
dB
7/23
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