LM2937
500 mA Low Dropout Regulator

General Description

The LM2937 is a positive voltage regulator capable of sup-
plying up to 500 mA of load current. The use of a PNP power
transistor provides a low dropout voltage characteristic. With
a load current of 500 mA the minimum input to output voltage
differential required for the output to remain in regulation is
typically 0.5V (1V guaranteed maximum over the full operat-
ing temperature range). Special circuitry has been incorpo-
rated to minimize the quiescent current to typically only
10 mA with a full 500 mA load current when the input to out-
put voltage differential is greater than 3V.

The LM2937 requires an output bypass capacitor for stabil-
ity. As with most low dropout regulators, the ESR of this ca-
pacitor remains a critical design parameter, but the LM2937
includes special compensation circuitry that relaxes ESR re-
quirements. The LM2937 is stable for all ESR below 3

. This

allows the use of low ESR chip capacitors.

Ideally suited for automotive applications, the LM2937 will
protect itself and any load circuitry from reverse battery con-

nections, two-battery jumps and up to +60V/-50V load dump
transients. Familiar regulator features such as short circuit
and thermal shutdown protection are also built in.

Features

Fully specified for operation over -40°C to +125°C

Output current in excess of 500 mA

Output trimmed for 5% tolerance under all operating
conditions

Typical dropout voltage of 0.5V at full rated load current

Wide output capacitor ESR range, up to 3

Internal short circuit and thermal overload protection

Reverse battery protection

60V input transient protection

Mirror image insertion protection

Connection Diagram and Ordering Information

TO-220 Plastic Package

DS011280-2

Front View

Order Number LM2937ET-5.0, LM2937ET-8.0,
LM2937ET-10, LM2937ET-12 or LM2937ET-15

See NS Package Number T03B

SOT-223 Plastic Package

DS011280-26

Front View

Order Number LM2937IMP-5.0,

LM2937IMP-8.0, LM2937IMP-10,

LM2937IMP-12 or LM2937IMP-15

See NS Package Number MP04A

TO-263 Surface-Mount Package

DS011280-5

Top View

DS011280-6

Side View

Order Number LM2937ES-5.0, LM2937ES-8.0,

LM2937ES-10, LM2937ES-12 or LM2937ES-15

See NS Package Number TS3B

March 2000

LM2937

500

Low

Dropout

Regulator

DS011280

www.national.com

Absolute Maximum Ratings

(Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Input Voltage

Continuous

26V

Transient (t

100 ms)

60V

Internal Power Dissipation (Note 2)

Internally Limited

Maximum Junction Temperature

150°C

Storage Temperature Range

-65°C to +150°C

TO-220 (10 seconds)

260°C

TO-263 (10 seconds)

230°C

SOT-223 (Vapor Phase, 60 seconds)

215°C

SOT-223 (Infared, 15 seconds)

220°C

ESD Susceptibility (Note 3)

2 kV

Operating Conditions

(Note 1)

Temperature Range (Note 2)

LM2937ET,

LM2937ES

-40°C

125°C

LM2937IMP

-40°C

85°C

Maximum Input Voltage

26V

Electrical Characteristics

= V

NOM

+ 5V, (Note 4) I

OUTmax

= 500 mA for the TO-220 and TO-263 packages, I

OUTmax

=400mA for the SOT-223 pack-

age, C

OUT

= 10 µF unless otherwise indicated. Boldface limits apply over the entire operating temperature range of the

indicated device., all other specifications are for T

= T

= 25°C.

Output Voltage (V

OUT

)

10V

Units

Parameter

Conditions

Typ

Limit

Typ

Limit

Typ

Limit

Output Voltage

5 mA

OUT

OUTmax

4.85

7.76

9.70

V(Min)

5.00

4.75

8.00

7.60

10.00

9.50

V(Min)

5.15

8.24

10.30

V(Max)

5.25

8.40

10.50

V(Max)

Line Regulation

OUT

+ 2V)

26V,

100

mV(Max)

OUT

= 5 mA

Load Regulation

5 mA

OUT

OUTmax

100

mV(Max)

Quiescent Current

OUT

+ 2V)

26V,

mA(Max)

OUT

= 5 mA

= (V

OUT

+ 5V),

mA(Max)

OUT

= I

OUTmax

Output Noise

10 Hz100 kHz

150

240

300

µVrms

Voltage

OUT

= 5 mA

Long Term Stability

1000 Hrs.

Dropout Voltage

OUT

= I

OUTmax

0.5

1.0

0.5

1.0

0.5

1.0

V(Max)

OUT

= 50 mA

110

250

110

250

110

250

mV(Max)

Short-Circuit Current

1.0

0.6

1.0

0.6

1.0

0.6

A(Min)

Peak Line Transient

100 ms, R

= 100

V(Min)

Voltage

Maximum Operational

V(Min)

Input Voltage

Reverse DC

OUT

-0.6V, R

= 100

-30

-15

-30

-15

-30

-15

V(Min)

Input Voltage

Reverse Transient

1 ms, R

= 100

-75

-50

-75

-50

-75

-50

V(Min)

Input Voltage

LM2937

www.national.com

Electrical Characteristics

= V

NOM

+ 5V, (Note 4) I

OUTmax

= 500 mA for the TO-220 and TO-263 packages, I

OUTmax

=400mA for the SOT-223 pack-

age, C

OUT

= 10 µF unless otherwise indicated. Boldface limits apply over the entire operating temperature range of the

indicted device., all other specifications are for T

= T

= 25°C.

Output Voltage (V

OUT

)

12V

15V

Units

Parameter

Conditions

Typ

Limit

Typ

Limit

Output Voltage

5 mA

OUT

OUTmax

11.64

14.55

V (Min)

12.00

11.40

15.00

14.25

V(Min)

12.36

15.45

V(Max)

12.60

15.75

V(Max)

Line Regulation

OUT

+ 2V)

26V,

120

150

mV(Max)

OUT

= 5 mA

Load Regulation

5 mA

OUT

OUTmax

120

150

mV(Max)

Quiescent Current

OUT

+ 2V)

26V,

mA(Max)

OUT

= 5 mA

= (V

OUT

+ 5V),

mA(Max)

OUT

= I

OUTmax

Output Noise

10 Hz100 kHz,

360

450

µVrms

Voltage

OUT

= 5 mA

Long Term Stability

1000 Hrs.

Dropout Voltage

OUT

= I

OUTmax

0.5

1.0

0.5

1.0

V(Max)

OUT

= 50 mA

110

250

110

250

mV(Max)

Short-Circuit Current

1.0

0.6

1.0

0.6

A(Min)

Peak Line Transient

100 ms, R

= 100

V(Min)

Voltage

Maximum Operational

V(Min)

Input Voltage

Reverse DC

OUT

-0.6V, R

= 100

-30

-15

-30

-15

V(Min)

Input Voltage

Reverse Transient

1 ms, R

= 100

-75

-50

-75

-50

V(Min)

Input Voltage

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
outside of its rated Operating Conditions.

Note 2: The maximum allowable power dissipation at any ambient temperature is P

MAX

= (125 - T

, where 125 is the maximum junction temperature for op-

eration, T

is the ambient temperature, and

is the junction-to-ambient thermal resistance. If this dissipation is exceeded, the die temperature will rise above 125°C

and the electrical specifications do not apply. If the die temperature rises above 150°C, the LM2937 will go into thermal shutdown. For the LM2937, the
junction-to-ambient thermal resistance

is 65°C/W, for the TO-220 package, 73°C/W for the TO-263 package, and 174°C/W for the SOT-223 package. When used

with a heatsink,

is the sum of the LM2937 junction-to-case thermal resistance

of 3°C/W and the heatsink case-to-ambient thermal resistance. If the TO-263

or SOT-223 packages are used, the thermal resistance can be reduced by increasing the P.C. board copper area thermally connected to the package (see Application
Hints for more information on heatsinking).

Note 3: ESD rating is based on the human body model, 100 pF discharged through 1.5 k

Note 4: Typicals are at T

= 25°C and represent the most likely parametric norm.

LM2937

www.national.com

Application Hints

EXTERNAL CAPACITORS

The output capacitor is critical to maintaining regulator stabil-
ity, and must meet the required conditions for both ESR
(Equivalent Series Resistance) and minimum amount of ca-
pacitance.

MINIMUM CAPACITANCE:

The minimum output capacitance required to maintain stabil-
ity is 10 µF (this value may be increased without limit).
Larger values of output capacitance will give improved tran-
sient response.

ESR LIMITS:

The ESR of the output capacitor will cause loop instability if
it is too high or too low. The acceptable range of ESR plotted
versus load current is shown in the graph below.

It is essen-

tial that the output capacitor meet these requirements,
or oscillations can result.

It is important to note that for most capacitors, ESR is speci-
fied only at room temperature. However, the designer must
ensure that the ESR will stay inside the limits shown over the
entire operating temperature range for the design.

For aluminum electrolytic capacitors, ESR will increase by
about 30X as the temperature is reduced from 25°C to
-40°C. This type of capacitor is not well-suited for low tem-
perature operation.

Solid tantalum capacitors have a more stable ESR over tem-
perature, but are more expensive than aluminum electrolyt-
ics. A cost-effective approach sometimes used is to parallel
an aluminum electrolytic with a solid Tantalum, with the total
capacitance split about 75/25% with the Aluminum being the
larger value.

If two capacitors are paralleled, the effective ESR is the par-
allel of the two individual values. The "flatter" ESR of the Tan-
talum will keep the effective ESR from rising as quickly at low
temperatures.

HEATSINKING

A heatsink may be required depending on the maximum
power dissipation and maximum ambient temperature of the
application. Under all possible operating conditions, the junc-
tion temperature must be within the range specified under
Absolute Maximum Ratings.

To determine if a heatsink is required, the power dissipated
by the regulator, P

, must be calculated.

The figure below shows the voltages and currents which are
present in the circuit, as well as the formula for calculating
the power dissipated in the regulator:

The next parameter which must be calculated is the maxi-
mum allowable temperature rise, T

(max). This is calcu-

lated by using the formula:

(max) = T

(max) - T

(max)

where: T

(max)

is the maximum allowable junction tem-
perature, which is 125°C for commercial
grade parts.

(max)

is the maximum ambient temperature
which will be encountered in the applica-
tion.

Using the calculated values for T

(max) and P

, the maxi-

mum allowable value for the junction-to-ambient thermal re-
sistance,

(J-A)

, can now be found:

(J-A)

= T

(max)/P

IMPORTANT: If the maximum allowable value for

(J-A)

found to be

53°C/W for the TO-220 package,

80°C/W for

the TO-263 package, or

174°C/W for the SOT-223 pack-

age, no heatsink is needed since the package alone will dis-
sipate enough heat to satisfy these requirements.

If the calculated value for

(J-A)

falls below these limits, a

heatsink is required.

HEATSINKING TO-220 PACKAGE PARTS

The TO-220 can be attached to a typical heatsink, or se-
cured to a copper plane on a PC board. If a copper plane is
to be used, the values of

(J-A)

will be the same as shown in

the next section for the TO-263.

If a manufactured heatsink is to be selected, the value of
heatsink-to-ambient thermal resistance,

(H-A)

, must first be

calculated:

(H-A)

(J-A)

(C-H)

(J-C)

Where:

(J-C)

is defined as the thermal resistance from
the junction to the surface of the case. A
value of 3°C/W can be assumed for

(J-C)

for this calculation.

(C-H)

is defined as the thermal resistance be-
tween the case and the surface of the heat-
sink. The value of

(C-H)

will vary from

about 1.5°C/W to about 2.5°C/W (depend-
ing on method of attachment, insulator,
etc.). If the exact value is unknown, 2°C/W
should be assumed for

(C-H)

When a value for

(H-A)

is found using the equation shown,

a heatsink must be selected that has a value that is less than
or equal to this number.

Output Capacitor ESR

DS011280-24

FIGURE 1. ESR Limits

DS011280-27

= I

÷ I

= (V

- V

OUT

) I

+ (V

) I

FIGURE 2. Power Dissipation Diagram

LM2937

www.national.com

Application Hints

(Continued)

(H-A)

is specified numerically by the heatsink manufacturer

in the catalog, or shown in a curve that plots temperature rise
vs power dissipation for the heatsink.

HEATSINKING TO-263 AND SOT-223 PACKAGE PARTS

Both the TO-263 ("S") and SOT-223 ("MP") packages use a
copper plane on the PCB and the PCB itself as a heatsink.
To optimize the heat sinking ability of the plane and PCB,
solder the tab of the package to the plane.

Figure 3 shows for the TO-263 the measured values of

(J-A)

for different copper area sizes using a typical PCB with 1
ounce copper

and no solder mask over the copper area used

for heatsinking.

As shown in the figure, increasing the copper area beyond 1
square inch produces very little improvement. It should also
be observed that the minimum value of

(J-A)

for the TO-263

package mounted to a PCB is 32°C/W.

As a design aid,

Figure 4 shows the maximum allowable

power dissipation compared to ambient temperature for the
TO-263 device (assuming

(J-A)

is 35°C/W and the maxi-

mum junction temperature is 125°C).

Figure 5 and Figure 6 show the information for the SOT-223
package.

Figure 6 assumes a

(J-A)

of 74°C/W for 1 ounce

copper and 51°C/W for 2 ounce copper and a maximum
junction temperature of 125°C.

SOT-223 SOLDERING RECOMMENDATIONS

It is not recommended to use hand soldering or wave solder-
ing to attach the small SOT-223 package to a printed circuit
board. The excessive temperatures involved may cause
package cracking.

Either vapor phase or infrared reflow techniques are pre-
ferred soldering attachment methods for the SOT-223 pack-
age.

DS011280-28

FIGURE 3.

(J-A)

vs Copper (1 ounce) Area for the

TO-263 Package

DS011280-29

FIGURE 4. Maximum Power Dissipation vs T

AMB

for

the TO-263 Package

DS011280-30

FIGURE 5.

(J-A)

vs Copper (2 ounce) Area for the

SOT-223 Package

DS011280-31

FIGURE 6. Maximum Power Dissipation vs T

AMB

for

the SOT-223 Package

LM2937

www.national.com

Physical Dimensions

inches (millimeters) unless otherwise noted (Continued)

LIFE SUPPORT POLICY

NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or

systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.

2. A critical component is any component of a life

support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.

National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com

National Semiconductor
Europe

Fax: +49 (0) 180-530 85 86

Email: europe.support@nsc.com

Deutsch Tel: +49 (0) 69 9508 6208
English

Tel: +44 (0) 870 24 0 2171

Français Tel: +33 (0) 1 41 91 8790

National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: ap.support@nsc.com

National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507

www.national.com

SOT-223 3-Lead Plastic Surface Mount Package

Order Number LM2937IMP-5.0, LM2937IMP-8.0, LM2937IMP-10, LM2937IMP-12 or LM2937IMP-15

NS Package Number MP04A

LM2937

500

Low

Dropout

Regulator

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LM2937ET-5.0

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LM2937ET-5.0