LM317.PDF

May 1996

LM117/LM317A/LM317

3-Terminal Adjustable Regulator

General Description

The LM117 series of adjustable 3-terminal positive voltage

regulators is capable of supplying in excess of 1.5A over a

1.2V to 37V output range. They are exceptionally easy to

use and require only two external resistors to set the output

voltage. Further, both line and load regulation are better

than standard fixed regulators. Also, the LM117 is packaged

in standard transistor packages which are easily mounted

and handled.

In addition to higher performance than fixed regulators, the

LM117 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 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 optional output

capacitor can be added to improve transient response. The

adjustment terminal can be bypassed to achieve very high

ripple rejection ratios which are difficult to achieve with stan-

dard 3-terminal regulators.

Besides replacing fixed regulators, the LM117 is useful in a

wide variety of other applications. Since the regulator is

``floating'' and sees only the input-to-output differential volt-

age, supplies of several hundred volts can be regulated as

long as the maximum input to output differential is not ex-

ceeded, i.e., avoid short-circuiting the output.

Also, it makes an especially simple adjustable switching reg-

ulator, a programmable output regulator, or by connecting a

fixed resistor between the adjustment pin and output, the

LM117 can be used as a precision current regulator. Sup-

plies with electronic shutdown can be achieved by clamping

the adjustment terminal to ground which programs the out-

put to 1.2V where most loads draw little current.

For applications requiring greater output current, see LM150

series (3A) and LM138 series (5A) data sheets. For the neg-

ative complement, see LM137 series data sheet.

LM117 Series Packages and Power Capability

Part Number

Rated Design

Package Power Load

Dissipation Current

Suffix

TO-3

20W 1.5A

TO-39

0.5A

TO-220

20W 1.5A

LCC

0.5A

TO-263

1.5A

Features

Y Guaranteed 1% output voltage tolerance

(LM317A)

Y Guaranteed max. 0.01%/V line regulation

(LM317A)

Y Guaranteed max. 0.3% load regulation

(LM117)

Y Guaranteed 1.5A output current

Y Adjustable output down to 1.2V

Y Current limit constant with temperature

Y P a Product Enhancement tested

Y 80 dB ripple rejection

Y Output is short-circuit protected

Typical Applications

1.2V±25V Adjustable Regulator

Digitally Selected Outputs

TL/H/9063±1

Full output current not available at high input-output voltages

*Needed if device is more than 6 inches from filter capacitors.

OptionalÐimproves transient response. Output capacitors in the range of

1 m F to 1000 m F of aluminum or tantalum electrolytic are commonly used

to provide improved output impedance and rejection of transients.

TL/H/9063±2

²²

V OUT e 1.25V

1 a

a I ADJ (R 2 )

*Sets maximum V OUT

C 1996 National Semiconductor Corporation

TL/H/9063

RRD-B30M56/Printed in U. S. A.

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Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

(Note 2)

Power Dissipation

Operating Temperature Range

LM117

b 55 § C s T J s a 150 § C

LM317A

b 40 § C s T J s a 125 § C

LM317

0 § C s T J s a 125 § C

Internally Limited

Preconditioning

Thermal Limit Burn-In

Input-Output Voltage Differential

a 40V, b 0.3V

All Devices 100%

Storage Temperature

b 65 § Cto a 150 § C

Lead Temperature

Metal Package (Soldering, 10 seconds)

300 § C

Plastic Package (Soldering, 4 seconds)

260 § C

ESD Tolerance (Note 5)

3 kV

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 3)

Parameter

Conditions

LM117 (Note 2)

Units

Min

Typ Max

Reference Voltage

3V s (V IN b V OUT ) s 40V,

1.20 1.25 1.30

10 mA s I OUT s I MAX ,P s P MAX

Line Regulation

3V s (V IN b V OUT ) s 40V (Note 4)

0.01 0.02 %/V

0.02 0.05 %/V

Load Regulation

10 mA s I OUT s I MAX (Note 4)

0.1

0.3 %

0.3

Thermal Regulation

20 ms Pulse

0.03

0.07 %/W

Adjustment Pin Current

100

m A

Adjustment Pin Current Change

10 mA s I OUT s I MAX

0.2

m A

3V s (V IN b V OUT ) s 40V

Temperature Stability

T MIN s T J s T MAX

Minimum Load Current

(V IN b V OUT ) e 40V

3.5

Current Limit

(V IN b V OUT ) s 15V

K Package

1.5

2.2

3.4

H, K Packages

0.5

0.8

1.8

(V IN b V OUT ) e 40V

K Package

0.3

0.4

H, K Packages

0.15

0.2

RMS Output Noise, % of V OUT

10 Hz s f s 10 kHz

0.003

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

Long-Term Stability

T J e 125 § C, 1000 hrs

0.3

Thermal Resistance,

K Package

2.3

§ C/W

Junction-to-Case

H Package

§ C/W

E Package

§ C/W

Thermal Resistance, Junction-

K Package

§ C/W

to-Ambient (No Heat Sink)

H Package

140

§ C/W

E Package

§ C/W

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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 3)

Parameter

Conditions

LM317A

LM317

Units

Min Typ Max Min Typ Max

Reference Voltage

1.238 1.250 1.262

3V s (V IN b V OUT ) s 40V,

1.225 1.250 1.270 1.20 1.25 1.30 V

10 mA s I OUT s I MAX ,P s P MAX

Line Regulation

3V s (V IN b V OUT ) s 40V (Note 4)

0.005 0.01

0.01 0.04 %/V

0.01 0.02

0.02 0.07 %/V

Load Regulation

10 mA s I OUT s I MAX (Note 4)

0.1

0.5

0.1 0.5 %

0.3 1

0.3 1.5 %

Thermal Regulation

20 ms Pulse

0.04 0.07

0.04 0.07 %/W

Adjustment Pin Current

50 100

50 100 m A

Adjustment Pin Current Change 10 mA s I OUT s I MAX

0.2 5

0.2 5 m A

3V s (V IN b V OUT ) s 40V

Temperature Stability

T MIN s T J s T MAX

Minimum Load Current

(V IN b V OUT ) e 40V

3.5 10

3.5 10 mA

Current Limit

(V IN b V OUT ) s 15V

K, T Packages

1.5 2.2 3.4 1.5 2.2 3.4 A

H, P Packages

0.5 0.8 1.8 0.5 0.8 1.8 A

(V IN b V OUT ) e 40V

K, T Packages

0.15 0.4

H, P Packages

0.075 0.2

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

0.003

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,

66 80

C ADJ e 10 m F

Long-Term Stability T J e 125 § C, 1000 hrs 0.3 1 0.3 1 %

Thermal Resistance, Junction- K Package 2.3 3 § C/W

to-Case H Package 12 15 12 15 § C/W

T Package 4 5 4 § C/W

P Package § C/W

Thermal Resistance, Junction- K Package 35 35 § C/W

to-Ambient (No Heat Sink) H Package 140 140 § C/W

T Package 50 50 § C/W

P Package (Note 6) 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.

The guaranteed specifications apply only for the test conditions listed.

Note 2: Refer to RETS117H drawing for the LM117H, or the RETS117K for the LM117K military specifications.

Note 3: Although power dissipation is internally limited, these specifications are applicable for maximum power dissipations of 2W for the TO-39 and 20W for the

TO-3 and TO-220. I MAX is 1.5A for the TO-3 and TO-220 packages and 0.5A for the TO-39 package. All limits (i.e., the numbers in the Min. and Max. columns) are

guaranteed to National's AOQL (Average Outgoing Quality Level).

Note 4: 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 5: Human body model, 100 pF discharged through a 1.5 k X resistor.

Note 6: If the TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package: Using

0.5 square inches of copper area. i JA is 50 § C/W; with 1 square inch of copper area, i JA is 37 § C/W; and with 1.6 or more square inches of copper area, i JA is

32 § C/W.

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Typical Performance Characteristics

Output Capacitor e 0 m F unless otherwise noted

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/9063±4

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Application Hints

In operation, the LM117 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

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. Any increase of the load capacitance larger

than 10 m F will merely improve the loop stability and output

impedance.

Load Regulation

The LM117 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 L .Ifthe

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/9063±5

FIGURE 1

Since the 100 m A current from the adjustment terminal rep-

resents an error term, the LM117 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

LM117 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 80 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 LM117 is stable with no output capacitors, like

any feedback circuit, certain values of external capacitance

can cause excessive ringing. This occurs with values be-

TL/H/9063±6

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. However, with the TO-5 package, care

should be taken to minimize the wire length of the output

lead. 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 LM117, this

discharge path is through a large junction that is able to

sustain 15A 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.

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