2001 Fairchild Semiconductor Corporation
www.fairchildsemi.com
Rev. 1.0.0
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 3.0 A over an
output voltage range of 1.2V to 33 V
1. Adj 2. Output 3. Input
1
TO-220
Internal Block Diagram
LM350
3-Terminal 3A Positive Adjustable Voltage
Regulator
LM350
2
Absolute Maximum Ratings
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)
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.
Parameter
Symbol
Value
Unit
Input-Output Voltage Differential
V
I
- V
O
35
V
DC
Lead Temperature (Soldering, 10sec)
T
LEAD
300
C
Power Dissipation
P
D
Internally limited
-
Operating Temperature Range
T
OPR
0 ~ +125
C
Storage Temperature Range
T
STG
-65 ~ +150
C
Parameter
Symbol
Conditions
Min.
Typ. Max.
Unit
Line Regulation (Note1)
Rline
T
A
= +25
C, 3V
V
I
-V
O
35V
-
0.015 0.03
%/V
Load Regulation (Note1)
Rload
T
A
= +25
C, 3V
V
I
-V
O
35V
V
O
5V
V
O
5V
-
5
0.1
25
0.5
mV
%
Adjustment Pin Current
I
ADJ
-
-
50
100
A
Adjustment Pin Current
Change
I
ADJ
3V
V
I
-V
O
35V,
10mA
I
o
3A, P
D
P
MAX
-
0.2
5.0
A
Thermal Regulation
REG
T
Pulse = 20ms, T
A
=+ 25
C
-
0.002
-
%/W
Reference Voltage
V
REF
3V
V
I
-V
O
35V, 10mA
I
O
3A,P
D
30W 1.2
1.25
1.30
V
Line Regulation
Rline
3.0V
V
I
-V
O
35V
-
0.02
0.07
%/W
Load Regulation
Rload
10mA
I
O
3.0A
V
O
5.0V
V
O
5.0V
-
20
0.3
70
1.5
mV
%
Temperature Stability
ST
T
T
J
= 0
C to + 125
C
-
1.0
-
%
Maximum Output Current
I
o(MAX)
V
I
-V
O
10V, P
D
P
MAX
3.0
4.5
-
A
V
I
-V
O
= 30V, P
D
P
MAX
,T
A
= +25
C
0.25
1.0
-
A
Minimum Load Current
I
L(MIN)
V
I
-V
O
= 35V
-
3.5
10
mA
RMS Noise, %of V
OUT
V
N
10Hz
f
10KHz, T
A
= +25
C
-
0.003
-
%/V
o
Ripple Rejection
RR
V
O
= 10V, f = 120Hz,
C
ADJ
= 0
C
ADJ
= 10
F
66
65
80
-
dB
dB
Long-Term Stability
ST
T
J
=+125
C
-
0.3
1
%/
1000HR
LM350
3
Typical Perfomance Characteristics
Figure 1. Load Regulation
Figure 3. Adjustment Pin Current
Figure 5. Temperature Stability
Figure 2. Current Limit
Figure 4. Dropout Voltage
Figure 6. Minimum Load Current
LM350
4
Typical Perfomance Characteristics (continued)
Figure 7. Ripple Rejection vs Vo
Figure 9. Ripple Rejection vs Frequency
Figure 11. Line Transient Response
Figure 8. Ripple Rejection vs Io
Figure 10. Output Impedance
Figure 12. Load Transient Response
LM350
5
Typical Application
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 1
F to 100
F 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 100
F) from the adjustment terminal represents an error term, the LM350 was designed to mini-
mize 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 100
A, the error associated with this term is negligible in most applications.
Input
Output
LM350
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