Datasheet LM2937 Datasheet (National Semiconductor)

LM2937
500 mA Low Dropout Regulator

LM2937 500 mA Low Dropout Regulator

March 2000

General Description

The LM2937 is a positive voltage regulator capable of sup­plying up to 500 mAofloadcurrent.TheuseofaPNPpower
transistor provides a low dropout voltage characteristic. With
a load current of 500 mAthe minimum input to output voltage
differential required for the output to remain in regulation is
typically 0.5V (1V guaranteed maximum over the full operat­ing temperature range). Special circuitry has been incorpo­rated to minimize the quiescent current to typically only
10 mA with a full 500 mA load current when the input to out­put voltage differential is greater than 3V.

The LM2937 requires an output bypass capacitor for stabil­ity.As with most low dropout regulators, the ESR of this ca­pacitor remains a critical design parameter, but the LM2937
includes special compensation circuitry that relaxes ESR re­quirements. The LM2937 is stable for all ESR below 3Ω. 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

n Fully specified for operation over −40˚C to +125˚C
n Output current in excess of 500 mA
n Output trimmed for 5% tolerance under all operating

conditions

n Typical dropout voltage of 0.5V at full rated load current
n Wide output capacitor ESR range, up to 3Ω
n Internal short circuit and thermal overload protection
n Reverse battery protection
n 60V input transient protection
n Mirror image insertion protection

Connection Diagram and Ordering Information

TO-220 Plastic Package

SOT-223 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

TO-263 Surface-Mount Package

DS011280-5

Top View

Order Number LM2937ES-5.0, LM2937ES-8.0,
LM2937ES-10, LM2937ES-12 or LM2937ES-15

See NS Package Number TS3B

DS011280-26

Front View

Order Number LM2937IMP-5.0,

LM2937IMP-8.0, LM2937IMP-10,

LM2937IMP-12 or LM2937IMP-15

See NS Package Number MP04A

DS011280-6

Side View

© 2000 National Semiconductor Corporation DS011280 www.national.com

Connection Diagram and Ordering Information (Continued)

LM2937

Temperature

Range

−40˚C ≤ T

−40˚C ≤ T

SOT-223 Package
Markings

The small physical size of the SOT-223 package does not allow sufficient space to provide the complete device part number. The actual devices will be labeled with
the package markings shown.

≤ 125˚C LM2937ES-5.0 LM2937ES-8.0 LM2937ES-10 LM2937ES-12 LM2937ES-15 TS3B TO-263

J

≤ 85˚C LM2937IMP-5.0 LM2937IMP-8.0 LM2937IMP-10 LM2937IMP-12 LM2937IMP-15 MP04A SOT-223

J

5.0 8.0 10 12 15 Package

LM2937ET-5.0 LM2937ET-8.0 LM2937ET-10 LM2937ET-12 LM2937ET-15 T03B TO-220

LM2937IMPX-5.0 LM2937IMPX-8.0 LM2937IMPX-10 LM2937IMPX-12 LM2937IMPX-15 MP04A SOT-223

L71B L72B L73B L74B L75B

Output Voltage NSC Package

Drawing

in Tape

and Reel

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LM2937

Absolute Maximum Ratings (Note 1)

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

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

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

Operating Conditions (Note 1)

Temperature Range (Note 2)

LM2937ET, LM2937ES −40˚C ≤ T
LM2937IMP −40˚C ≤ T

Maximum Input Voltage 26V

≤125˚C

J

≤85˚C

J

TO-220 (10 seconds) 260˚C

Electrical Characteristics

VIN=V
age, C
indicated device., all other specifications are for T

Output Voltage 5 mA ≤ I

Line Regulation (V

Load Regulation 5 mA ≤ I
Quiescent Current (V

Output Noise 10 Hz–100 kHz 150 240 300 µVrms
Voltage I
Long Term Stability 1000 Hrs. 20 32 40 mV
Dropout Voltage I

Short-Circuit Current 1.0 0.6 1.0 0.6 1.0 0.6 A(Min)
Peak Line Transient t
Voltage
Maximum Operational 26 26 26 V(Min)
Input Voltage
Reverse DC V
Input Voltage
Reverse Transient t
Input Voltage

+ 5V, (Note 4) I

NOM

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

OUT

Output Voltage (V

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

OUTmax

= 25˚C.

A=TJ

) 5V 8V 10V Units

OUT

=400mA for the SOT-223 pack-

OUTmax

Parameter Conditions Typ Limit Typ Limit Typ Limit

OUT

≤ I

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)

+ 2V) ≤ VIN≤ 26V, 15 50 24 80 30 100 mV(Max)

OUT

I

=5mA

OUT

≤ I

OUT

OUTmax

+ 2V) ≤ VIN≤ 26V, 2 10 2 10 2 10 mA(Max)

OUT

I

=5mA

OUT

V

=(V

IN

I

OUT=IOUTmax

OUT

OUT=IOUTmax

I

OUT

<

100 ms, RL= 100Ω 75 60 75 60 75 60 V(Min)

f

OUT

<

1 ms, RL= 100Ω −75 −50 −75 −50 −75 −50 V(Min)

r

+ 5V), 10 20 10 20 10 20 mA(Max)

OUT

=5mA

= 50 mA 110 250 110 250 110 250 mV(Max)

≥ −0.6V, RL= 100Ω −30 −15 −30 −15 −30 −15 V(Min)

5 50 8 80 10 100 mV(Max)

0.5 1.0 0.5 1.0 0.5 1.0 V(Max)

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Electrical Characteristics

VIN=V

LM2937

age, C
indicted device., all other specifications are for T

Output Voltage 5 mA ≤ I

Line Regulation (V

Load Regulation 5 mA ≤ I
Quiescent Current (V

Output Noise 10 Hz–100 kHz, 360 450 µVrms
Voltage I
Long Term Stability 1000 Hrs. 44 56 mV
Dropout Voltage I

Short-Circuit Current 1.0 0.6 1.0 0.6 A(Min)
Peak Line Transient t
Voltage
Maximum Operational 26 26 V(Min)
Input Voltage
Reverse DC V
Input Voltage
Reverse Transient t
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
eration, T
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 θ
with a heatsink, θ
or SOT-223 packages are used, the thermal resistance can be reduced by increasing the P.C.boardcopper 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 kΩ.
Note 4: Typicals are at T

+ 5V, (Note 4) I

NOM

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

OUT

Output Voltage (V

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

OUTmax

= 25˚C.

A=TJ

) 12V 15V Units

OUT

=400mA for the SOT-223 pack-

OUTmax

Parameter Conditions Typ Limit Typ Limit

OUT

≤ I

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)

+ 2V) ≤ VIN≤ 26V, 36 120 45 150 mV(Max)

OUT

I

=5mA

OUT

≤ I

OUT

OUTmax

+ 2V) ≤ VIN≤ 26V, 2 10 2 10 mA(Max)

OUT

I

=5mA

OUT

V

=(V

IN

I

OUT=IOUTmax

OUT

OUT=IOUTmax

I

OUT

<

100 ms, RL= 100Ω 75 60 75 60 V(Min)

f

OUT

<

1 ms, RL= 100Ω −75 −50 −75 −50 V(Min)

r

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

A

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

is the sum of the LM2937 junction-to-case thermal resistance θJCof 3˚C/W and the heatsink case-to-ambient thermal resistance. If the TO-263

JA

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

J

JA

+ 5V), 10 20 10 20 mA(Max)

OUT

=5mA

= 50 mA 110 250 110 250 mV(Max)

≥ −0.6V, RL= 100Ω −30 −15 −30 −15 V(Min)

12 120 15 150 mV(Max)

0.5 1.0 0.5 1.0 V(Max)

= (125 − TA)/θJA, where 125 is the maximum junction temperature for op-

MAX

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Typical Performance Characteristics

LM2937

Dropout Voltage vs
Output Current

Quiescent Current vs
Temperature

DS011280-7

Dropout Voltage vs
Temperature

Quiescent Current vs
Input Voltage

DS011280-8

Output Voltage vs
Temperature

DS011280-9

Quiescent Current vs
Output Current

Line Transient Response

Output Impedance

DS011280-10

DS011280-13

Load Transient Response

Maximum Power
Dissipation (TO-220)

DS011280-11

DS011280-14

DS011280-12

Ripple Rejection

DS011280-15

Maximum Power Dissipation
(TO-263) (Note 2)

DS011280-16

DS011280-17

DS011280-18

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Typical Performance Characteristics (Continued)

LM2937

Low Voltage Behavior

Low Voltage Behavior

Low Voltage Behavior

Output at Voltage
Extremes

Peak Output Current

DS011280-19

DS011280-22

Output at Voltage
Extremes

DS011280-20

DS011280-23

DS011280-21

Output Capacitor ESR

DS011280-24

DS011280-25

Typical Application

* Required if the regulator is located more than 3 inches from the power supply filter capacitors.

*

Required for stability. C

*
equivalent series resistance, ESR, of this capacitor may be as high as 3Ω.

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must be at least 10 µF (over the full expected operating temperature range) and located as close as possible to the regulator. The

out

DS011280-1

Application Hints

EXTERNAL CAPACITORS

The output capacitor is critical to maintaining regulator stabil­ity, and must meet the required conditions for both ESR
(Equivalent Series Resistance) and minimum amount of ca­pacitance.

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 tran­sient 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.

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

Output Capacitor ESR

DS011280-24

FIGURE 1. ESR Limits

It is important to note that for most capacitors, ESR is speci­fied 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 tem­perature operation.

Solid tantalum capacitors have a more stable ESR over tem­perature, but are more expensive than aluminum electrolyt­ics. 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 theAluminum being the
larger value.

If two capacitors are paralleled, the effective ESR is the par­allel of the two individual values.The “flatter” ESR of the Tan­talum 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 junc­tion 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.

D

It is essen-

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:

DS011280-27

IIN=IL÷I
PD=(VIN−V

G

OUT)IL

+(VIN)I

G

FIGURE 2. Power Dissipation Diagram

The next parameter which must be calculated is the maxi­mum allowable temperature rise, T

(max). This is calcu-

R

lated by using the formula:

T

(max) = TJ(max) − TA(max)

R

where: T

(max) is the maximum allowable junction tem-

J

perature, which is 125˚C for commercial
grade parts.

T

(max) is the maximum ambient temperature

A

which will be encountered in the applica­tion.

Using the calculated values for T

(max) and PD, the maxi-

R

mum allowable value for the junction-to-ambient thermal re­sistance, θ

IMPORTANT: If the maximum allowable value for θ

, can now be found:

(J−A)

θ

(J−A)=TR

(max)/P

D

(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 pack­age, no heatsink is needed since the package alone will dis­sipate enough heat to satisfy these requirements.

If the calculated value for θ

falls below these limits, a

(J−A)

heatsink is required.

HEATSINKING TO-220 PACKAGE PARTS

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

will be the same as shown in

(J−A)

the next section for the TO-263.
If a manufactured heatsink is to be selected, the value of

heatsink-to-ambient thermal resistance, θ

, must first be

(H−A)

calculated:

θ

Where: θ

= θ

(H−A)

is defined as the thermal resistance from

(J−C)

(J−A)

− θ

(C−H)

− θ

(J−C)

the junction to the surface of the case. A
value of 3˚C/W can be assumed for θ

(J−C)

for this calculation.

θ

(C−H)

is defined as the thermal resistance be­tween the case and the surface of the heat­sink. The value of θ

will vary from

(C−H)

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

When a value for θ

is found using the equation shown,

(H−A)

(C−H)

.

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

LM2937

is

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Application Hints (Continued)

θ

LM2937

is specified numerically by the heatsink manufacturer

(H−A)

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

and no solder mask over the copper area used

for heatsinking.

(J−A)

FIGURE 5. θ

DS011280-30

vs Copper (2 ounce) Area for the

(J−A)

SOT-223 Package

DS011280-28

FIGURE 3. θ

vs Copper (1 ounce) Area for the

(J−A)

TO-263 Package

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 θ

for the TO-263

(J−A)

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 θ

is 35˚C/W and the maxi-

(J−A)

mum junction temperature is 125˚C).

DS011280-29

FIGURE 4. Maximum Power Dissipation vs T

AMB

for

the TO-263 Package

Figure 5

package.

and

Figure 6

Figure 6

show the information for the SOT-223

assumes a θ

of 74˚C/W for 1 ounce

(J−A)

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

DS011280-31

FIGURE 6. Maximum Power Dissipation vs T

AMB

for

the SOT-223 Package

SOT-223 SOLDERING RECOMMENDATIONS

It is not recommended to use hand soldering or wave solder­ing 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 pre­ferred soldering attachment methods for the SOT-223 pack­age.

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Physical Dimensions inches (millimeters) unless otherwise noted

Plastic Package

Order Number LM2937ET-5.0,

LM2937ET-8.0, LM2937ET-10, LM2937ET-12,

or LM2937ET-15

NS Package Number T03B

LM2937

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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

LM2937

TO-263 3-Lead Plastic Surface Mount Package

Order Number LM2937ES-5.0, LM2937ES-8.0, LM2937ES-10, LM2937ES-12 or LM2937ES-15

NS Package Number TS3B

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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

LM2937 500 mA Low Dropout Regulator

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

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