STMICROELECTRONICS LM350

LM350
Three-terminal 3 A adjustable voltage regulators
Features
■
Guaranteed 3 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
Table 1.
TO-3
Device summary
Order codes
February 2008
TO-3
Temperature range
LM350K
0 to 125 °C
Rev 2
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Contents
LM350
Contents
1
Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5
Typical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6
Application hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1
External capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.2
Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.3
Protection diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7
Application circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
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LM350
Diagram
1
Diagram
Figure 1.
Schematic diagram
3/14
Pin configuration
2
Pin configuration
Figure 2.
Pin connections (bottom view)
4/14
LM350
LM350
Maximum ratings
3
Maximum ratings
Table 2.
Absolute maximum ratings
Symbol
PD
VI - VO
Parameter
Power dissipation
Unit
Internally limited
Input-output voltage differential
TSTG
Storage temperature range
TLEAD
lead temperature (Soldering, 10 seconds)
TOP
Value
Operating junction temperature range
35
V
-65 to 150
°C
300
°C
0 to 125
°C
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
RthJC
Thermal resistance junction-case
1.5
°C/W
RthJA
Thermal resistance junction-ambient
35
°C/W
5/14
Electrical characteristics
LM350
4
Electrical characteristics
Table 4.
Electrical characteristics (VI -VO = 5V, IO = 1.5 A. Although power dissipation is internally
limited, these specifications apply to power dissipation up to 30 W, unless otherwise
specified)
Symbol
Parameter
Test conditions
Typ.
Max.
Unit
0.005
0.03
%/V
VO ≤5 V
5
25
mV
VO ≥ 5 V
0.1
0.5
%
0.002
0.02
%/W
50
100
µA
0.2
5
µA
1.24
1.29
V
0.02
0.05
%/V
VO ≤5 V
20
70
mV
VO ≥ 5 V
0.3
1.5
%
KVI
Line regulation (1)
Ta = 25°C, VI - VO = 3 to 35 V
KVO
Load regulation (1)
Ta = 25°C
IO = 10 mA to 3 A
Thermal regulation
Pulse = 20 ms
IADJ
Adjustment pin current
ΔIADJ
Adjustment pin current
change
IL = 10 mA to 3 A, VI - VO = 3 to 35 V
VREF
Reference voltage
VI - VO = 3 to 35 V, IO = 10 mA to 3 A
P ≤30 W
KVI
Line regulation (1)
VI - VO = 3 to 35 V
KVO
Load regulation (1)
IO = 10 mA to 3 A
KVT
Temperature stability
TJ = TMIN to TMAX
IO(MIN)
Minimum load current
VI - VO ≤35 V
IO(MAX) Current limit
VNO
RMS output noise
(% of VO)
RVF
Ripple rejection ratio
KVH
Long term stability
Min.
VI - VO ≤10 V
1.19
1
3.5
DC
3
mA
4.5
1
0.001
VO = 10 V, f = 120 Hz
Ta = 125°C
10
A
VI - VO = 30 V
Ta = 25°C, f = 10 Hz to 10 kHz
CADJ = 10 µF
%
%
65
dB
66
86
0.3
1
%
1. Regulation is measured at constant junction temperature. Changes in output voltage due to heating effects are taken into
account separately by thermal rejection.
6/14
LM350
Typical performance
5
Typical performance
Figure 3.
1.2 V to 25 V adjustable regulator
Δ Needed if device is far from filter capacitors.
* Optional-improves transient response. Output capacitors in the range of 1 µF to 100 µF of aluminium or
tantalum electrolytic are commonly used to provide improved output impedance and rejection of transients
** VO = 1.25 V (1 + R2/R1)
7/14
Application hints
6
LM350
Application hints
In operation, the LM350 develops a nominal 1.25 V reference voltage, V(REF), between the
output and adjustment terminal. The reference voltage is impressed 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:
VO = V(REF) (1+ R2 / R1) + IADJ x R2.
Figure 4.
Circuit
Since the 50 µA current from the adjustment terminal represents an error term, the LM350
was designed to minimize IADJ 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 will rise.
6.1
External capacitors
An input bypass capacitor is recommended. A 0.1 µF disc or 1 µF solid tantalum on the input
is suitable input by passing for almost all applications. The device is more sensitive to the
absence of input bypassing when adjustment or output capacitors are used by the above
values will eliminate the possibility of problems.
The adjustment terminal can be bypassed to ground on the LM350 to improve ripple
rejection. This bypass capacitor prevents ripple form being amplified as the output voltage is
increased. With a 10 µF bypass capacitor 75 dB ripple rejection is obtainable at any output
level. Increases over 20 µF do not appreciably improve the ripple rejection at frequencies
above 120 Hz. If the bypass capacitor is used, it is sometimes necessary to include
protection diodes to prevent the capacitor from discharging through internal low current
paths and damaging the device.
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 25 µF in aluminium electrolytic to equal 1 µF solid tantalum at high frequencies.
Ceramic capacitors are also good at high frequencies, but some types have a large
8/14
LM350
Application hints
decrease in capacitance at frequencies around 0.5 MHz. For this reason, 0.01 µF disc may
seem to work better than a 0.1 µF disc as a bypass.
Although the LM350 is stable with no output capacitors, like any feedback circuit, certain
values of external capacitance can cause excessive ringing. This occurs with values
between 500 pF and 5000 pF. A 1 µF solid tantalum (or 25 µF aluminium electrolytic) on the
output swamps this effect and insures stability.
6.2
Load regulation
The LM350 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 terminal and the output terminal (usually 240 Ω) 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 15 V
regulator with 0.05 Ω resistance between the regulator and load will have a load regulation
due to line resistance of 0.05 Ω x IL. If the set resistor is connected near the load the
effective line resistance will be 0.05 Ω (1 + R2/R1) or in this case, 11.5 times worse.
Figure 5 shows the effect of resistance between the regulator and 140 Ω set resistor. With
the TO-3 package, it is easy to minimize the resistance 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 regulation.
6.3
Protection diodes
When external capacitors are used with any IC regulator it is sometimes necessary to add
protection diodes to prevent the capacitors from discharging through low current points into
the regulator. Most 20 µF capacitors have low enough internal series resistance to deliver
20 A spikes when shorted. Although the surge is short, there is enough energy to damage
parts of the IC.
When an output capacitor is connected to a regulator and the input is shorted, the output
capacitor will discharge into the output of the regulator. The discharge current depends on
the value of the capacitor, the output voltage of the regulator, and the rate of decrease of VI.
In the LM350 this discharge path is through a large junction that is able to sustain 25 A
surge with no problem. This is not true of other types of positive regulators. For output
capacitors of 100 µF or less at output of 15 V or less, there is no need to use diodes.
The bypass capacitor on the adjustment terminal can discharge through a low current
junction. Discharge occurs when either the input or output is shorted. Internal to the LM350
is a 50 Ω resistor which limits the peak discharge current. No protection is needed for output
voltages of 25 V or less and 10 µF capacitance. Figure 6 shows an LM350 with protection
diodes included for use with outputs greater than 25 V and high values of output
capacitance.
9/14
Application circuits
7
Application circuits
Figure 5.
Regulator with line resistance in output lead
Figure 6.
Regulator with protection diodes
10/14
LM350
LM350
8
Package mechanical data
Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK®
packages. These packages have a lead-free second level interconnect. The category of
second Level Interconnect is marked on the package and on the inner box label, in
compliance with JEDEC Standard JESD97. The maximum ratings related to soldering
conditions are also marked on the inner box label. ECOPACK is an ST trademark.
ECOPACK specifications are available at: www.st.com.
11/14
Package mechanical data
LM350
TO-3 mechanical data
mm.
Dim.
Min.
A
inch.
Typ.
Max.
Min.
Typ.
11.85
B
0.96
Max.
0.466
1.05
1.10
0.037
0.041
0.043
C
1.70
0.066
D
8.7
0.342
E
20.0
0.787
G
10.9
0.429
N
16.9
0.665
P
26.2
R
3.88
1.031
4.09
U
0.152
39.5
V
1.555
30.10
1.185
A
P
D
C
O
N
B
V
E
G
U
0.161
R
P003C/C
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LM350
Revision history
9
Revision history
Table 5.
Document revision history
Date
Revision
29-Sep-2006
1
11-Feb-2008
2
Changes
Added: Table 1 on page 1.
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LM350
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