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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
TO-3
Table 1.
Device summary
Order codes TO-3 LM350K Temperature range 0 to 125 C
February 2008
Rev 2
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Contents
LM350
Contents
1 2 3 4 5 6 Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Typical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Application hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1 6.2 6.3 External capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Protection diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7 8 9
Application circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
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LM350
Diagram
1
Figure 1.
Diagram
Schematic diagram
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Pin configuration
LM350
2
Figure 2.
Pin configuration
Pin connections (bottom view)
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LM350
Maximum ratings
3
Table 2.
Symbol PD VI - VO TSTG TLEAD TOP
Maximum ratings
Absolute maximum ratings
Parameter Power dissipation Input-output voltage differential Storage temperature range lead temperature (Soldering, 10 seconds) Operating junction temperature range Value Internally limited 35 -65 to 150 300 0 to 125 V C C C Unit
Note:
Absolute maximum ratings are those values beyond which damage to the device may occur. Functional operation under these condition is not implied Thermal data
Parameter Thermal resistance junction-case Thermal resistance junction-ambient Value 1.5 35 Unit C/W C/W
Table 3.
Symbol RthJC RthJA
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Electrical characteristics
LM350
4
Table 4.
Electrical characteristics
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)
Parameter Line regulation (1) Load regulation (1) Thermal regulation IADJ Adjustment pin current Adjustment pin current change Reference voltage Line regulation (1) Load regulation (1) Temperature stability Minimum load current IL = 10 mA to 3 A, VI - VO = 3 to 35 V VI - VO = 3 to 35 V, IO = 10 mA to 3 A P 30 W VI - VO = 3 to 35 V IO = 10 mA to 3 A TJ = TMIN to TMAX VI - VO 35 V VI - VO 10 V DC VI - VO = 30 V 3 VO 5 V VO 5 V 1.19 Test conditions Ta = 25C, VI - VO = 3 to 35 V Ta = 25C IO = 10 mA to 3 A Pulse = 20 ms VO 5 V VO 5 V Min. Typ. 0.005 5 0.1 0.002 50 0.2 1.24 0.02 20 0.3 1 3.5 4.5 A 1 0.001 65 dB 66 86 0.3 1 % % 10 Max. 0.03 25 0.5 0.02 100 5 1.29 0.05 70 1.5 Unit %/V mV % %/W A A V %/V mV % % mA
Symbol KVI KVO
IADJ VREF KVI KVO KVT IO(MIN)
IO(MAX) Current limit VNO RVF KVH RMS output noise (% of VO) Ripple rejection ratio Long term stability
Ta = 25C, f = 10 Hz to 10 kHz VO = 10 V, f = 120 Hz CADJ = 10 F Ta = 125C
1. Regulation is measured at constant junction temperature. Changes in output voltage due to heating effects are taken into account separately by thermal rejection.
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LM350
Typical performance
5
Figure 3.
Typical performance
1.2 V to 25 V adjustable regulator
Needed if device is far from filter capacitors. * Optional-improves transient response. Output capacitors in the range of 1 F to 100 F of aluminium or tantalum electrolytic are commonly used to provide improved output impedance and rejection of transients ** VO = 1.25 V (1 + R2/R1)
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Application hints
LM350
6
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 A 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 F disc or 1 F 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 F bypass capacitor 75 dB ripple rejection is obtainable at any output level. Increases over 20 F 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 F in aluminium electrolytic to equal 1 F solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies, but some types have a large
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LM350
Application hints decrease in capacitance at frequencies around 0.5 MHz. For this reason, 0.01 F disc may seem to work better than a 0.1 F 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 F solid tantalum (or 25 F 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 ) 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 resistance between the regulator and load will have a load regulation due to line resistance of 0.05 x IL. If the set resistor is connected near the load the effective line resistance will be 0.05 (1 + R2/R1) or in this case, 11.5 times worse. Figure 5 shows the effect of resistance between the regulator and 140 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 F 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 F 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 resistor which limits the peak discharge current. No protection is needed for output voltages of 25 V or less and 10 F capacitance. Figure 6 shows an LM350 with protection diodes included for use with outputs greater than 25 V and high values of output capacitance.
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Application circuits
LM350
7
Figure 5.
Application circuits
Regulator with line resistance in output lead
Figure 6.
Regulator with protection diodes
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LM350
Package mechanical data
8
Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK(R) 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.
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Package mechanical data
LM350
TO-3 mechanical data
Dim. A B C D E G N P R U V 30.10 3.88 10.9 16.9 26.2 4.09 39.5 1.185 0.152 0.96 mm. Min. Typ. 11.85 1.05 1.10 1.70 8.7 20.0 0.429 0.665 1.031 0.161 1.555 0.037 Max. Min. inch. Typ. 0.466 0.041 0.043 0.066 0.342 0.787 Max.
P G
A
D C
U
V
O
N
R
P003C/C
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B
E
LM350
Revision history
9
Table 5.
Date
Revision history
Document revision history
Revision 1 2 Added: Table 1 on page 1. Changes
29-Sep-2006 11-Feb-2008
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LM350
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