LM238K [STMICROELECTRONICS]
THREE-TERMINAL 5 A ADJUSTABLE VOLTAGE REGULATORS; 三端5的可调稳压器
| 型号： | LM238K |
| 厂家： | 
ST |
| 描述： | THREE-TERMINAL 5 A ADJUSTABLE VOLTAGE REGULATORS |
| 文件： | 总12页 (文件大小：187K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM138/238
LM338
THREE-TERMINAL 5-A
ADJUSTABLE VOLTAGE REGULATORS
.
.
.
.
.
.
.
GUARANTEED 7A PEAK OUTPUT CURRENT
GUARANTEED 5A OUTPUT CURRENT
ADJUSTABLE OUTPUT DOWN TO 1.2V
LINE REGULATION TYPICALLY 0.005% /V
LOAD REGULATION TYPICALLY 0.1%
GUARANTEED THERMAL REGULATION
CURRENT LIMIT CONSTANT WITH TEM-
PERATURE
.
STANDARD 3-LEAD TRANSISTOR PACKAGE
DESCRIPTION
The LM138/LM238/LM338 are adjustable 3-terminal
positive voltageregulators capable of supplying in ex-
cess of 5A over a 1.2V to 32V output range. They are
exceptionally easy to use and require only 2 resistors
toset the output voltage. Careful circuitdesign has re-
sulted in outstanding load and line regulation com-
parable to many commercial power supplies. The
LM138 family is supplied in a standard 3-lead transis-
tor package.
TO3
K SUFFIX
(Steel Can)
ORDER CODE
A unique feature of the LM138 family is time-de-
pendent current limiting. The current limit circuitry
allowspeak currents of upto 12A tobe drawn fromthe
regulator for short periods of time. This allows the
LM138 to be used with heavy transient loads and
speedsstart-up under full-load conditions. Under sus-
tained 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 thepower transistor. Overloadpro-
tection remains functional even if the adjustment pin
is accidentally disconnected.
Normally, nocapacitors are needed unless thedevice
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 res-
ponse. The adjustment terminal can be bypassed to
achieve very high ripple rejection ratios which are dif-
ficult to achieve with standard 3-terminal regulators.
Besidesreplacing fixedregulators ordiscretedesigns,
the LM238 is useful in a wide variety of other applica-
tions. Since the regulator is ”floating” and sees only
theinput-to-output differential voltage, supplies of sev-
eral 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 packages. The LM138 is rated
for operation from -55 oC to 150 oC, the LM238 from
– 25°C to + 150°C and the LM338 from 0°C to +
125°C.
PART
NUMBER
TEMPERATURE
RANGE
PACKAGE
K
o
o
LM138
LM238
LM338
-55 C to + 150 C
•
•
•
o
o
-25 C to + 150 C
o
o
0 C to + 125 C
EXAMPLE: LM138K
PIN CONNECTION
(bottom view)
Case is output
March 1993
1/12
LM138-LM238-LM338
ABSOLUTE MAXIMUM RATING
Symbol
Parameter
Value
Internally Limited
35
Unit
W
Ptot
Power Dissipation
VI - VO Input-Output Voltage DIfferential
V
oC
Toper Operating Junction Temperature Range
LM138
LM238
LM338
-55 to 150
-25 to 150
0 to 125
Tstg
Storage Temperature Range
-65 to 150
300
oC
oC
Tlead
Lead Temperature (Soldering, 10 seconds)
THERMAL CHARACTERISTICS
Symbol
Parameter
Value
1.4
Unit
oC/W
oC/W
Rth(j-c) Typical Junction-Case Thermal Resistance
Rth(j-a) Max Junction-Ambient Thermal Resistance
35
SCHEMATIC DIAGRAM
2/12
LM138-LM238-LM338
ELECTRICAL CHARACTERISTICS
o
LM138: -55 ≤ Tj ≤ 150 C, VI - VO = 5V, IO = 2.5A
o
LM238: -25 ≤ Tj ≤ 150 C, VI - VO = 5V, IO = 2.5A
o
LM338: 0 ≤ Tj ≤ 150 C, VI - VO = 5V, IO = 2.5A
Although power dissipation is internally limited, these specifications apply to power dissipation up to
50W (unless otherwise specified).
Symbol
KVI
Parameter
LM138-LM238
LM338
Typ.
0.005 0.03
Unit
Min.
Typ.
Max.
Min.
Max.
Line Regulation - (note 1)
0.005 0.01
%/V
Tamb = 25 oC, 3 V ≤ (VI - VO) ≤ 35 V
KVO
Load Regulation Tamb = 25 oC, 10 mA ≤ IO ≤ 5 A
VO ≤ 5V - (note 1)
5
15
5
0.1
25
0.5
mV
%
VO ≥ 5V - (note 1)
0.1
0.3
Thermal Regulation (pulse = 20 ms)
Adjustment Pin Current
Adjustment Pin Current Change
0.002 0.01
0.002 0.02
%/W
µA
µA
Iadj
∆Iadj
45
100
5
45
100
5
0.2
0.2
10 mA ≤ IL ≤ 5 A, 3 V ≤ (VI - VO) ≤ 35 V
v(ref)
KVI
Reference Voltage
3V ≤ (VI - VO) ≤ 35 V, 10 mA ≤ IO ≤ 5A, P ≤ 50W
Line Regulation - (note 1)
1.19
1.24
0.02
1.29
0.04
1.19
1.24
0.02
1.29
0.06
V
%/V
3 V ≤ (VI - VO) ≤ 35 V
KVO
Load Regulation 10 mA ≤ IO ≤ 5 A
VO ≤ 5V - (note 1)
20
0.3
1
30
0.6
20
0.3
1
50
1
mV
%
%
VO ≥ 5V - (note 1)
Temperature Stability (Tmin ≤ Tj ≤ Tmax
KVT
)
IO(min) Minimum Load Current (VI - VO ≤ 35 V)
IO(max) Current Limit (VI - VO ≤ 10 V)
DC
3.5
5
0.003
1
3.5
10
0.003
1
mA
A
5
7
8
12
1
5
7
8
12
1
0.5 ms Peak
VI - VO = 30 V
RMS Output Noise, % of VO
(Tamb = 25 oC, 10 Hz ≤ f ≤ 10 KHz)
%
Rvf
Ripple Rejection Ratio
VO = 10 V, f = 120 Hz
Cadi = 10 µF
Long Term Stability (Tamb = 125 oC)
dB
60
75
0.3
60
75
0.3
60
60
KVH
%
Note 1 : Regulation is measured at constant junction temperature. Changes in output voltage due to heating effects are taken
into account separately by thermal rejection.
3/12
LM138-LM238-LM338
4/12
LM138-LM238-LM338
5/12
LM138-LM238-LM338
TYPICAL APPLICATIONS
Since the 50µA current from the adjustment termi-
nal represents an error term, the LM338 was de-
signed to minimize Iadj and make it very constant
with line and load changes. To do this, allquiescent
operating current is returned to the output establi-
shing a minimum load current requirement. If there
is insufficient load on the output, the outputwill rise.
+ 1.2V to + 25V ADJUSTABLE REGULATOR
EXTERNAL CAPACITORS
An input bypass capacitor is recommended. A
0.1µF disc or 1µF solid tantalum on the input is suit-
able input by passing for almost all applications.
The device ismore sensitiveto the absenceofinput
bypassing when adjustment or output capacitors
are used byt the above values will eliminate the
possibility of problems.
The adjustment terminal can be bypassed to
ground on the LM338 to improve ripple rejection.
This bypass capacitor prevents ripple form being
amplified as the output voltage is increased. With
a 10µF bypass capacitor 75dB ripple rejection is
obtainable at any output level. Increases over20µF
do not appreciably improve the ripple rejection at
frequencies above 120Hz. If the bypass capacitor
is used, it is sometimes necessary to include pro-
tection diodes to prevent the capacitor from dis-
charging through internal low current paths and
damaging the device.
∆ Needed if device is far from filter capacitors.
*
Optional-improves transient response. Output capacitors in the
range of 1µF to 100µF of aluminium or tantalum electrolytic are
commonly used to provide improved output impedance and rejec-
tion of tran-sients.
R2
* * VO = 1.25V (1 +
)
R1
* * * R1 = 240Ω for LM138 and LM238
APPLICATION HINTS
In general, the best type of capacitors to use are
solid tantalum. Solid tantalum capacitors have low
impedance even at high frequencies. Depending
upon capacitor construction, it takes about 25µF in
aluminum electrolyticto equal1µF solid tantalum at
high frequencies. Ceramic capacitors are also
good at high frequencies, but some types have a
large decrease in capacitance at frequencies
around 0.5MHz. For this reason, 0.01µF disc may
seem to work better than a 0.1µF disc as a bypass.
In operation, the LM338 develops a nominal 1.25V
reference voltage, V(ref), between the output and
adjustment terminal. The reference voltage is im-
pressed across program resistor R1 and, since the
voltage is constant, a constant current I1 then flows
through the output set resistor R2, giving an output
voltage of
R2
VO = V(ref) ( 1+
) + IadjR2
R1
Although the LM338 is stable with no output capa-
citors, like any feedback circuit, certain values of
external capacitance can cause excessive ringing.
This occurs with values between 500pF and
5000pF. A 1µF solid tantalum (or 25µF aluminium
electrolytic) on the output swamps this effect and
insures stability.
Figure 1.
LOAD REGULATION
The LM338 is capable of providing extremely good
load regulation but a few precautions are needed
to obtain maximum performance. The current set
resistor connected between the adjustment termi-
nal and the output terminal (usually 240Ω) should
be tied directly to the output of the regulator rather
than near the load. This eliminates line drops from
appearing effectively in series with the reference
and degrading regulation. For example, a 15V
regulator with 0.05Ω resistance between the regu-
lator and load will have a load regulation due to line
resistance of 0.05Ω x IL. If the set resistor is con-
nected near the load the effective line resistance
6/12
LM138-LM238-LM338
will be 0.05Ω (1 + R2/R1) or in this case, 11.5 times
20µF capacitors have low enough internal series re-
sistance to deliver 20A spikes when shorted. Al-
thoughthe surge is short, there is enough energy to
damage parts of the IC.
worse.
Figure 2 shows the effect of resistance between the
regulator and 140Ω set resistor.
When an output capacitor is connected to a regula-
tor and the input is shorted, the output capacitor will
discharge into the output of the regulator. The dis-
charge current depends on the value of the capaci-
tor, the output voltage of the regulator, and the rate
of decrease of VI. In the LM338 this discharge path
is through a large junction that is able to sustain 25A
surge withno problem. Thisis not true ofother types
of positive regulators. For output capacitors of
100µF or less at output of 15V or less, there is no
need to use diodes.
With the TO-3 package, it is easy tominimize the re-
sistance from the case to the set resistor, by using
2 separate leads to the case. The ground of R2 can
be returned near the ground of the load to provide
remote ground sensing and improve load regula-
tion.
PROTECTION DIODES
When external capacitors are used withany IC regu-
lator it is sometimes necessary to add protection
diodes to prevent the capacitors from discharging
through low current points into the regulator. Most
The bypass capacitor on the adjustment terminal
can discharge through a low current junction. Dis-
charge occurs when either the input or output is
shorted. Internal to the LM338 is a 50Ω resistor
which limits the peak discharge current. No protec-
tion is needed for output voltages of 25V or less and
10µF capacitance. Figure 3 shows an LM338 with
protection diodes included for use with outputs
greater than 25V and high values of output capacit-
ance.
Figure 2 : Regulator with Line Resistance in Out-
put Lead.
Figure 3 : Regulator with Protection Diodes.
7/12
LM138-LM238-LM338
10A REGULATOR
*
Minimum load – 100mA
VI ≥ 10V
V0 ≥ 3V
VI – V0 ≥ 3.5V
5A CURRENT REGULATOR
*
Minimum load – 100mA
VI ≥ 10V
V0 ≥ 3V
VI – V0 ≥ 3.5V
8/12
LM138-LM238-LM338
15A REGULATOR
*
Minimum load – 100mA
VI ≥ + 10V
V0 ≥ + 3V
VI – V0 ≥ + 4V
5V LOGIC REGULATOR WITH ELECTRONIC SHUTDOWN**
*
*
*
R1 = 240Ω for LM138 or LM238
R2 = 720Ω for LM138 or LM238
Minimum output ≈ + 1.2V
*
9/12
LM138-LM238-LM338
TRACKING PREREGULATOR
*
*
*
R1 = 240Ω for LM138 or LM238
R2 = 720Ω for LM138 or LM238
Minimum output ≈ + 1.2V
*
SLOW TURN-ON 15V REGULATOR
*
*
R1 = 240Ω
R2 = 2.7kΩ
} for LM138 and LM238
10/12
LM138-LM238-LM338
TO-3 MECHANICAL DATA
mm
inch
DIM.
MIN.
11.00
0.97
TYP.
MAX.
13.10
1.15
MIN.
0.433
0.038
0.059
0.327
0.748
0.421
0.649
0.984
0.157
1.515
1.187
TYP.
MAX.
0.516
0.045
0.065
0.351
0.787
0.437
0.677
1.023
0.161
1.547
1.193
A
B
C
D
E
G
N
P
R
U
V
1.50
1.65
8.32
8.92
19.00
10.70
16.50
25.00
4.00
20.00
11.10
17.20
26.00
4.09
38.50
30.00
39.30
30.30
A
D
P
C
G
R
P003F
11/12
LM138-LM238-LM338
Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsability for the
consequences of use of such information nor for any infringement of patents or other rights of third parties which may results from its use. No
license is granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specificationsmentioned
in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied.
SGS-THOMSON Microelectronicsproductsare notauthorized foruse ascritical componentsin life support devices or systems without express
written approval of SGS-THOMSON Microelectonics.
1994 SGS-THOMSON Microelectronics - All Rights Reserved
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