www.fairchildsemi.com
LM350
3-Terminal 3A Positive Adjustable Voltage
Regulator
Features
•
•
•
•
•
•
•
Output Adjustable Between 1.2V and 33V
Guaranteed 3A Output Current
Internal Thermal Overload Protection
Load Regulation (Typ: 0.1%)
Line Regulation (Typ: 0.015%/V)
Internal Short Circuit Current Limit
Output Transistor Safe-Area Compensation
Description
The LM350 is an adjustable 3-terminal positive voltage
regulator capable of supplying in excess of 3.0A over an
output voltage range of 1.2V to 33V
TO-220
1
1. Adj 2. Output 3. Input
Internal Block Diagram
3
INPUT
+
V
REF
VOLTAGE
REFERENCE
PROTECTION
CIRCUITRY
R
SC
Q
1
_
Q
0
ADJUSTABLE
OUTPUT
2
1
Rev. 1.0.1
©2009 Fairchild Semiconductor Corporation
LM350
Absolute Maximum Ratings
Parameter
Input Output Voltage Differential
Lead Temperature (Soldering, 10sec)
Power Dissipation
Operating Temperature Range
Storage Temperature Range
Symbol
V
I
- V
O
T
LEAD
P
D
T
OPR
T
STG
Value
35
300
Internally limited
0 ~ +125
-65 ~ +150
Unit
V
DC
°C
-
°C
°C
Electrical Characteristics
(V
I
-V
O
= 5V, I
O
= 1.5A, T
J
= 0°C to +125°C; P
D
≤
P
DMAX
, unless otherwise specified)
Parameter
Line Regulation (Note1)
Load Regulation (Note1)
Adjustment Pin Current
Adjustment Pin Current
Change
Thermal Regulation
Reference Voltage
Line Regulation
Load Regulation
Temperature Stability
Maximum Output Current
Minimum Load Current
RMS Noise, %of V
OUT
Ripple Rejection
Long-Term Stability
Symbol
Rline
Rload
I
ADJ
ΔI
ADJ
REG
T
V
REF
Rline
Rload
ST
T
I
o(MAX)
I
L(MIN)
V
N
RR
ST
Conditions
T
A
= +25°C, 3V
≤
V
I
-V
O
≤
35V
T
A
= +25°C, 3V
≤
V
I
-V
O
≤
35V
V
O
≤
5V
V
O
≥
5V
-
3V
≤
V
I
-V
O
≤
35V,
10mA
≤
I
o
≤
3A, P
D
≤
P
MAX
Pulse = 20ms, T
A
=+25°C
3V
≤
V
I
-V
O
≤
35V, 10mA
≤I
O
≤
3A,P
D
≤
30W
3.0V
≤
V
I
-V
O
≤
35V
10mA
≤
I
O
≤
3.0A
V
O
≤
5.0V
V
O
≥
5.0V
T
J
= 0°C to +125°C
V
I
-V
O
≤
10V, P
D
≤
P
MAX
V
I
-V
O
= 30V, P
D
≤
P
MAX
,T
A
= +25°C
V
I
-V
O
= 35V
10Hz
≤
f
≤
10kHz, T
A
= +25°C
V
O
= 10V, f = 120Hz,
C
ADJ
= 0
C
ADJ
= 10μF
T
J
= +125°C
Min.
-
-
-
-
-
1.2
-
-
-
3.0
0.25
-
-
Typ.
Max.
Unit
%/V
mV
%
μA
μA
%/W
V
%/W
mV
%
%
A
A
mA
%/V
o
dB
dB
%/
1000HR
0.015 0.03
5
0.1
50
0.2
0.002
1.25
0.02
20
0.3
1.0
4.5
1.0
3.5
0.003
65
80
0.3
25
0.5
100
5.0
-
1.30
0.07
70
1.5
-
-
-
10
-
-
1
66
-
Note:
1. Regulation is measured at constant junction temperature. Changes in output voltage due to heating effects must be taken into
account separately. Pulse testing with low duty cycle is used.
2
LM350
Typical Performance Characteristics
Figure 1. Load Regulation
Figure 2. Current Limit
Figure 3. Adjustment Pin Current
Figure 4. Dropout Voltage
Figure 5. Temperature Stability
Figure 6. Minimum Load Current
3
LM350
Typical Performance Characteristics
(Continued)
Figure 7. Ripple Rejection vs Vo
Figure 8. Ripple Rejection vs Io
Figure 9. Ripple Rejection vs Frequency
Figure 10. Output Impedance
Figure 11. Line Transient Response
Figure 12. Load Transient Response
4
LM350
Typical Application
LM350
IN
Input
ADJ
OUT
I
1
R
1
120
C
O
1uF
Output
I
ADJ
C
I
0.1uF
R
2
Figure 13.
C
I
: C
I
is required if the regulator is located an appreciable distance from power supply filter.
C
O
: Output capacitors in the range of 1μF to 100μF of aluminum or tantalum electronic are commonly used to provide
improved output impedance and rejection of transients.
In operation, the LM350 develops a nominal 1.25V reference voltage, V
REF
, between the output and adjustment terminal. The
reference voltage is impressed across program resistor R
1
and, since the voltage is constant, a constant current I
1
then flows
through the output set resistor R
2
, giving an output voltage of
V
O
= 1.25V(1+R
2
/R
1
) + I
ADJ
R
2
Since I
ADJ
current (less than 100μA) from the adjustment terminal represents an error term, the LM350 was designed to
minimize I
ADJ
and make it very constant with line and load changes. To do this, all quiescent operating current is returned to
the output establishing a minimum load current requirement. If there is insufficient load on the output, the output voltage will
rise. Since the LM350 is a floating regulator, it is only the voltage differential across the circuit which is important to
performance, and operation at high voltage with respect to ground is possible.
Since I
ADJ
is controlled to less than 100μA, the error associated with this term is negligible in most applications.
5
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