LM350.PDF

January 1995

LM150, LM350A/LM350

3-Amp Adjustable Regulators

General Description

The LM150 series of adjustable 3-terminal positive voltage

regulators is capable of supplying in excess of 3A over a

1.2V to 33V output range. They are exceptionally easy to

use and require only 2 external resistors to set the output

voltage. Further, both line and load regulation are compara-

ble to discrete designs. Also, the LM150 is packaged in

standard transistor packages which are easily mounted and

handled.

In addition to higher performance than fixed regulators, the

LM150 series offers full overload protection available only in

IC's. Included on the chip are current limit, thermal overload

protection and safe area protection. All overload protection

circuitry remains fully functional even if the adjustment ter-

minal is accidentally disconnected.

Normally, no capacitors are needed unless the device is

situated more than 6 inches from the input filter capacitors

in which case an input bypass is needed. An output capaci-

tor can be added to improve transient response, while by-

passing the adjustment pin will increase the regulator's rip-

ple rejection.

Besides replacing fixed regulators or discrete designs, the

LM150 is useful in a wide variety of other applications. Since

the regulator is ``floating'' and sees only the input-to-output

differential voltage, supplies of several hundred volts can be

regulated as long as the maximum input to output differen-

tial is not exceeded, i.e., avoid short-circuiting the output.

By connecting a fixed resistor between the adjustment pin

and output, the LM150 can be used as a precision current

regulator. Supplies with electronic shutdown can be

achieved by clamping the adjustment terminal to ground

which programs the output to 1.2V where most loads draw

little current.

The part numbers in the LM150 series which have a K suffix

are packaged in a standard Steel TO-3 package, while

those with a T suffix are packaged in a TO-220 plastic pack-

age. The LM150 is rated for b 55 § C s T J s a 150 § C, while

the LM350A is rated for b 40 § C s T J s a 125 § C, and the

LM350 is rated for 0 § C s T J s a 125 § C.

Features

Y Adjustable output down to 1.2V

Y Guaranteed 3A output current

Y Guaranteed thermal regulation

Y Output is short circuit protected

Y Current limit constant with temperature

Y P a Product Enhancement tested

Y 86 dB ripple rejection

Y Guaranteed 1% output voltage tolerance (LM350A)

Y Guaranteed max. 0.01%/V line regulation (LM350A)

Y Guaranteed max. 0.3% load regulation (LM350A)

Applications

Y Adjustable power supplies

Y Constant current regulators

Y Battery chargers

Connection Diagrams

(TO-3 STEEL)

Metal Can Package

(TO-220)

Plastic Package

Case is Output

TL/H/9061±5

TL/H/9061±4

Front View

Order Number LM350AT or LM350T

See NS Package Number T03B

Bottom View

Order Number LM150K STEEL

or LM350K STEEL

See NS Package Number K02A

Order Number LM150K/883

See NS Package Number K02C

C 1995 National Semiconductor Corporation

TL/H/9061

RRD-B30M115/Printed in U. S. A.

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

(Note 4)

Power Dissipation

Lead Temperature

Metal Package (Soldering, 10 sec.)

300 § C

Plastic Package (Soldering, 4 sec.)

260 § C

ESD Tolerance

TBD

Internally Limited

Operating Temperature Range

LM150

Input-Output Voltage Differential

a 35V

b 55 § C s T J s a 150 § C

Storage Temperature

b 65 § Cto a 150 § C

LM350A

b 40 § C s T J s a 125 § C

LM350

0 § C s T J s a 125 § C

Electrical Characteristics

Specifications with standard type face are for T J e 25 § C, and those with boldface type apply over full Operating Tempera-

ture Range. Unless otherwise specified, V IN b V OUT e 5V, and I OUT e 10 mA. (Note 2)

Parameter

Conditions

LM150

Units

Min

Typ Max

Reference Voltage

3V s (V IN b V OUT ) s 35V,

1.20 1.25 1.30 V

10 mA s I OUT s 3A, P s 30W

Line Regulation

3V s (V IN b V OUT ) s 35V (Note 3)

0.005 0.01 %/V

0.02 0.05 %/V

Load Regulation

10 mA s I OUT s 3A (Note 3)

0.1

0.3 %

0.3

1 %

Thermal Regulation

20 ms Pulse

0.002 0.01 %/W

Adjustment Pin Current

50 100 m A

Adjustment Pin Current Change 10 mA s I OUT s 3A, 3V s (V IN b V OUT ) s 35V

0.2

m A

Temperature Stability

T MIN s T J s T MAX

Minimum Load Current

V IN b V OUT e 35V

3.5

5 mA

Current Limit

V IN b V OUT s 10V

3.0 4.5

V IN b V OUT e 30V

0.3

RMS Output Noise, % of V OUT

10 Hz s f s 10 kHz

0.001

Ripple Rejection Ratio

V OUT e 10V, f e 120 Hz, C ADJ e 0 m F

V OUT e 10V, f e 120 Hz, C ADJ e 10 m F

66 86

Long-Term Stability

T J e 125 § C, 1000 hrs

0.3

1 %

Thermal Resistance, Junction

K Package

1.2

1.5

§ C/W

to Case

Thermal Resistance, Junction

K Package

§ C/W

to Ambient (No Heat Sink)

Electrical Characteristics (Continued)

Specifications with standard type face are for T J e 25 § C, and those with boldface type apply over full Operating Tempera-

ture Range. Unless otherwise specified, V IN b V OUT e 5V, and I OUT e 10 mA. (Note 2) (Continued)

Parameter

Conditions

LM350A

LM350

Units

Min Typ Max Min Typ Max

Reference Voltage

I OUT e 10 mA, T J e 25 § C

1.238 1.250 1.262

3V s (V IN b V OUT ) s 35V,

1.225 1.250 1.270 1.20 1.25 1.30 V

10 mA s I OUT s 3A, P s 30W

Line Regulation 3V s (V IN b V OUT ) s 35V (Note 3) 0.005 0.01 0.005 0.03 %/V

0.02 0.05 0.02 0.07 %/V

Load Regulation 10 mA s I OUT s 3A (Note 3) 0.1 0.3 0.1 0.5 %

0.3 1 0.3 1.5 %

Thermal Regulation 20 ms Pulse 0.002 0.01 0.002 0.03 %/W

Adjustment Pin Current 50 100 50 100 m A

Adjustment Pin Current Change 10 mA s I OUT s 3A, 3V s (V IN b V OUT ) s 35V 0.2 5 0.2 5 m A

Temperature Stability T MIN s T J s T MAX 1 1 %

Minimum Load Current V IN b V OUT e 35V 3.5 10 3.5 10 mA

Current Limit V IN b V OUT s 10V 3.0 4.5 3.0 4.5 A

V IN b V OUT e 30V 0.3 1 0.25 1 A

RMS Output Noise, % of V OUT 10 Hz s f s 10 kHz 0.001 0.001 %

Ripple Rejection Ratio V OUT e 10V, f e 120 Hz, C ADJ e 0 m F 65 65 dB

V OUT e 10V, f e 120 Hz, C ADJ e 10 m F 66 86 66 86 dB

Long-Term Stability T J e 125 § C, 1000 hrs 0.25 1 0.25 1 %

Thermal Resistance, Junction K Package 1.2 1.5 § C/W

to Case T Package 3 4 3 4 § C/W

Thermal Resistance, Junction K Package 35 § C/W

to Ambient (No Heat Sink) T Package 50 50 § C/W

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.

Note 2: These specifications are applicable for power dissipations up to 30W for the TO-3 (K) package and 25W for the TO-220 (T) package. Power dissipation is

guaranteed at these values up to 15V input-output differential. Above 15V differential, power dissipation will be limited by internal protection circuitry. All limits (i.e.,

the numbers in the Min. and Max. columns) are guaranteed to National's AOQL (Average Outgoing Quality Level).

Note 3: Regulation is measured at a constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are

covered under the specifications for thermal regulation.

Note 4: Refer to RETS150K drawing for military specifications of the LM150K.

Typical Performance Characteristics

Load Regulation

Current Limit

Adjustment Current

Dropout Voltage

Temperature Stability

Minimum Operating Current

Ripple Rejection

Output Impedance

Line Transient Response

Load Transient Response

TL/H/9061±6

Application Hints

In operation, the LM150 develops a nominal 1.25V refer-

ence voltage, V REF , between the output and adjustment ter-

minal. The reference voltage is impressed across program

resistor R1 and, since the voltage is constant, a constant

current I 1 then flows through the output set resistor R2, giv-

ing an output voltage of

LOAD REGULATION

The LM150 is capable of providing extremely good load reg-

ulation but a few precautions are needed to obtain maxi-

mum performance. The current set resistor connected be-

tween the adjustment terminal and the output terminal (usu-

ally 240 X ) should be tied directly to the output (case) 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

0.05 X resistance between the regulator and load will have a

load regulation due to line resistance of 0.05 X c I OUT .If

the set resistor is connected near the load the effective line

resistance will be 0.05 X (1 a R2/R1) or in this case, 11.5

times worse.

Figure2shows the effect of resistance between the regula-

tor and 240 X set resistor.

V OUT e V REF

1 a R2

a I ADJ R2.

TL/H/9061±7

FIGURE 1

Since the 50 m A current from the adjustment terminal repre-

sents an error term, the LM150 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 will rise.

EXTERNAL CAPACITORS

An input bypass capacitor is recommended. A 0.1 m F disc

or 1 m F solid tantalum on the input is suitable input bypass-

ing for almost all applications. The device is more sensitive

to the absence of input bypassing when adjustment or out-

put capacitors are used but the above values will eliminate

the possibility of problems.

The adjustment terminal can be bypassed to ground on the

LM150 to improve ripple rejection. This bypass capacitor

prevents ripple from being amplified as the output voltage is

increased. With a 10 m F bypass capacitor 86 dB ripple re-

jection is obtainable at any output level. Increases over

10 m 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 pre-

vent the capacitor from discharging through internal low cur-

rent paths and damaging the device.

In general, the best type of capacitors to use is solid tanta-

lum. Solid tantalum capacitors have low impedance even at

high frequencies. Depending upon capacitor construction, it

takes about 25 m F in aluminum electrolytic to equal 1 m F

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 0.5 MHz.

For this reason, 0.01 m F disc may seem to work better than

a 0.1 m F disc as a bypass.

Although the LM150 is stable with no output capacitors, like

any feedback circuit, certain values of external capacitance

can cause excessive ringing. This occurs with values be-

tween 500 pF and 5000 pF. A 1 m F solid tantalum (or 25 m F

aluminum electrolytic) on the output swamps this effect and

insures stability.

TL/H/9061±8

FIGURE 2. Regulator with Line Resistance

in Output Lead

With the TO-3 package, it is easy to minimize the resistance

from the case to the set resistor, by using two 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.

PROTECTION DIODES

When external capacitors are used withany IC regulator it is

sometimes necessary to add protection diodes to prevent

the capacitors from discharging through low current points

into the regulator. Most 10 m F capacitors have low enough

internal series resistance to deliver 20A spikes when short-

ed. 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 regu-

lator, and the rate of decrease of V IN . In the LM150, this

discharge path is through a large junction that is able to

sustain 25A surge with no problem. This is not true of other

types of positive regulators. For output capacitors of 25 m F

or less, there is no need to use diodes.

The bypass capacitor on the adjustment terminal can dis-

charge through a low current junction. Discharge occurs

when either the input or output is shorted. Internal to the

LM150 is a 50 X resistor which limits the peak discharge

current. No protection is needed for output voltages of 25V

or less and 10 m F capacitance. Figure3 shows an LM150

with protection diodes included for use with outputs greater

than 25V and high values of output capacitance.

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