LM138 - LM238 - LM338
Three-terminal 5 A adjustable voltage regulators
Features
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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
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.
Description
The LM138, LM238, LM338 are adjustable 3-
terminal 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.
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A unique feature of the LM138 family is time-de-
pendent 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
Table 1.
Device summary
Part numbers
LM138
LM238
LM338
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Order codes
LM138K
LM238K
LM338K
Temperature range
-55 °C to 150 °C
-25 °C to 150 °C
0 °C to 125 °C
April 2008
Rev 2
1/23
www.st.com
23
Contents
LM138 - LM238 - LM338
Contents
1
2
3
4
5
6
7
Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Typical application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Application hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1
7.2
7.3
External capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Protection diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8
9
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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Power technology
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