LM2937-2.5,LM2937-3.3
LM2937-2.5, LM2937-3.3 400mA and 500mA Voltage Regulators
Literature Number: SNVS015D
LM2937-2.5, LM2937-3.3
400mA and 500mA Voltage Regulators
General Description
The LM2937-2.5 and LM2937-3.3 are positive voltage regu-
lators capable of supplying up to 500 mA of load current.
Both regulators are ideal for converting a common 5V logic
supply, or higher input supply voltage, to the lower 2.5V and
3.3V supplies to power VLSI ASIC’s and microcontrollers.
Special circuitry has been incorporated to minimize the qui-
escent current to typically only 10 mA with a full 500 mA load
current when the input to output voltage differential is greater
than 5V.
The LM2937 requires an output bypass capacitor for stabil-
ity. As with most regulators utilizing a PNP pass transistor,
the ESR of this capacitor remains a critical design param-
eter, but the LM2937-2.5 and LM2937-3.3 include special
compensation circuitry that relaxes ESR requirements. The
LM2937 is stable for all ESR ratings less than 5Ω. This
allows the use of low ESR chip capacitors.
The regulators are also suited for automotive applications,
with built in protection from reverse battery connections,
two-battery jumps and up to +60V/−50V load dump tran-
sients. Familiar regulator features such as short circuit and
thermal shutdown protection are also built in.
Features
nFully specified for operation over −40˚C to +125˚C
nOutput current in excess of 500 mA (400mA for
SOT-223 package)
nOutput trimmed for 5% tolerance under all operating
conditions
nWide output capacitor ESR range, 0.01Ωup to 5Ω
nInternal short circuit and thermal overload protection
nReverse battery protection
n60V input transient protection
nMirror image insertion protection
Connection Diagrams and Ordering Information
TO-220 Plastic Package SOT-223 Plastic Package
10011324
Front View
Order Number LM2937ET-2.5, LM2937ET-3.3,
See NS Package Number T03B
10011325
Front View
Order Number LM2937IMP-2.5, LM2937IMP-3.3,
See NS Package Number MA04A
TO-263 Surface-Mount Package
10011326
Top View
10011327
Side View
Order Number LM2937ES-2.5, LM2937ES-3.3,
See NS Package Number TS3B
August 2005
LM2937-2.5, LM2937-3.3 400mA and 500mA Voltage Regulators
© 2005 National Semiconductor Corporation DS100113 www.national.com
Connection Diagrams and Ordering Information (Continued)
Temperature
Range
Output Voltage NSC Package
2.5 3.3 Package
Drawing
−40˚C ≤T
A
≤125˚C LM2937ES-2.5 LM2937ES-3.3 TS3B TO-263
LM2937ET-2.5 LM2937ET-3.3 T03B TO-220
−40˚C ≤T
A
≤85˚C LM2937IMP-2.5 LM2937IMP-3.3 MA04A SOT-223
SOT-223 Package
Markings
L68B L69B
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.
LM2937-2.5, LM2937-3.3
www.national.com 2
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
Lead Temperature Soldering
TO-220 (10 seconds) 260˚C
TO-263 (10 seconds) 230˚C
SOT-223 (Vapor Phase, 60 seconds) 215˚C
SOT-223 (Infrared, 15 seconds) 220˚C
ESD Susceptibility (Note 3) 2 kV
Operating Conditions(Note 1)
Temperature Range (Note 2)
LM2937ES, LM2937ET −40˚C ≤T
A
≤
125˚C
LM2937IMP −40˚C ≤T
A
≤85˚C
Input Voltage Range 4.75V to 26V
Electrical Characteristics(Note 4)
V
IN
=V
NOM
+ 5V, I
OUTmax
= 500 mA for the TO-220 and TO-263 packages, I
OUTmax
=400mA for the SOT-223 package, C
OUT
=
10 µF unless otherwise indicated. Boldface limits apply over the entire operating temperature range, of the indicated de-
vice, all other specifications are for T
A
=T
J
= 25˚C.
Output Voltage (V
OUT
) 2.5V 3.3V Units
Parameter Conditions Typ Limit Typ Limit
Output Voltage 5 mA ≤I
OUT
≤I
OUTmax
2.42 3.20 V (Min)
2.5 2.38 3.3 3.14 V(Min)
2.56 3.40 V(Max)
2.62 3.46 V(Max)
Line Regulation(Note 5) 4.75V ≤V
IN
≤26V, 7.5 25 9.9 33 mV(Max)
I
OUT
=5mA
Load Regulation 5 mA ≤I
OUT
≤I
OUTmax
2.5 25 3.3 33 mV(Max)
Quiescent Current 7V ≤V
IN
≤26V, 2 10 210 mA(Max)
I
OUT
=5mA
V
IN
=(V
OUT
+ 5V), 10 20 10 20 mA(Max)
I
OUT
=I
OUTmax
V
IN
= 5V, I
OUT
=I
OUTmax
66 100125 66 100125 mA(Max)
Output Noise 10 Hz–100 kHz, 75 99 µVrms
Voltage I
OUT
=5mA
Long Term Stability 1000 Hrs. 10 13.2 mV
Short-Circuit Current 1.0 0.6 1.0 0.6 A(Min)
Peak Line Transient t
f
<100 ms, R
L
= 100Ω75 60 75 60 V(Min)
Voltage
Maximum Operational 26 26 V(Min)
Input Voltage
Reverse DC V
OUT
≥−0.6V, R
L
= 100Ω−30 −15 −30 −15 V(Min)
Input Voltage
Reverse Transient t
r
<1 ms, R
L
= 100Ω−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 PMAX = (125 − TA)/θJA, where 125 is the maximum junction temperature for
operation, TAis the ambient temperature, and θJA 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 regulator will go into thermal shutdown. The junction-to-ambient
thermal resistance θJA 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,
θJA is the sum of the device junction-to-case thermal resistance θJC 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 kΩ.
Note 4: Typicals are at TJ= 25˚C and represent the most likely parametric norm.
LM2937-2.5, LM2937-3.3
www.national.com3
Electrical Characteristics(Note 4) (Continued)
Note 5: The minimum input voltage required for proper biasing of these regulators is 4.75V. Below this level the outputs will fall out of regulation. This effect is not
the normal dropout characteristic where the output falls out of regulation due to the PNP pass transistor entering saturation. If a value for worst case effective input
to output dropout voltage is required in a specification, the values should be 2.37V maximum for the LM2937-2.5 and 1.6V maximum for the LM2937-3.3.
Typical Performance Characteristics
Output Voltage vs
Temperature (2.5V)
Output Voltage vs
Temperature (3.3V)
10011302 10011303
Quiescent Current vs
Output Current (2.5V)
Quiescent Current vs
Output Current (3.3V)
10011304 10011305
Quiescent Current vs
Input Voltage (2.5V)
Quiescent Current vs
Input Voltage (3.3V)
10011306 10011307
LM2937-2.5, LM2937-3.3
www.national.com 4
Typical Performance Characteristics (Continued)
Low Voltage Behavior (2.5V) Low Voltage Behavior (3.3)
10011314 10011315
Output at Voltage
Extremes Output Capacitor ESR
10011316 10011317
Peak Output Current
10011318
LM2937-2.5, LM2937-3.3
www.national.com 6
Typical Application
10011301
* Required if the regulator is located more than 3 inches from the power supply filter capacitors.
** Required for stability. Cout must be at least 10 µF (over the full expected operating temperature range) and located as close as possible to the regulator. The
equivalent series resistance, ESR, of this capacitor may be as high as 3Ω.
LM2937-2.5, LM2937-3.3
www.national.com7
Application Hints
EXTERNAL CAPACITORS
The output capacitor is critical to maintaining regulator sta-
bility, 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 sta-
bility 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
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 tem-
perature operation.
Solid tantalum capacitors have a more stable ESR over
temperature, but are more expensive than aluminum elec-
trolytics. 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
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 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
D
, 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
R
(max). This is calcu-
lated by using the formula:
T
R
(max) = T
J
(max) − T
A
(max)
where: T
J
(max) is the maximum allowable junction tem-
perature, which is 125˚C for commercial
grade parts.
T
A
(max) is the maximum ambient temperature
which will be encountered in the
application.
Using the calculated values for T
R
(max) and P
D
, the maxi-
mum allowable value for the junction-to-ambient thermal
resistance, θ
(J−A)
, can now be found:
θ
(J−A)
=T
R
(max)/P
D
IMPORTANT: If the maximum allowable value for θ
(J−A)
is
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
dissipate enough heat to satisfy these requirements.
If the calculated value for θ
(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 θ
(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, θ
(H−A)
, must first be
calculated:
θ
(H−A)
=θ
(J−A)
−θ
(C−H)
−θ
(J−C)
Where: θ
(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 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
(C−H)
will vary from about 1.5˚C/W to
about 2.5˚C/W (depending on method of at-
tachment, insulator, etc.). If the exact value is
unknown, 2˚C/W should be assumed for
θ
(C−H)
.
Output Capacitor ESR
10011317
FIGURE 1. ESR Limits
10011319
IIN =I
L÷I
G
PD=(V
IN −V
OUT)I
L+(V
IN)I
G
FIGURE 2. Power Dissipation Diagram
LM2937-2.5, LM2937-3.3
www.national.com 8
Application Hints (Continued)
When a value for θ
(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.
θ
(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 θ
(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 θ
(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 θ
(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 θ
(J−A)
of 74˚C/W for 1 ounce
copper and 51˚C/W for 2 ounce copper and a maximum
junction temperature of +85˚C.
Please see AN1028 for power enhancement techniques to
be used with the SOT-223 package.
SOT-223 SOLDERING RECOMMENDATIONS
It is not recommended to use hand soldering or wave sol-
dering 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.
10011320
FIGURE 3. θ
(J−A)
vs Copper (1 ounce) Area for the
TO-263 Package
10011321
FIGURE 4. Maximum Power Dissipation vs T
AMB
for
the TO-263 Package
10011322
FIGURE 5. θ
(J−A)
vs Copper (2 ounce) Area for the
SOT-223 Package
10011323
FIGURE 6. Maximum Power Dissipation vs T
AMB
for
the SOT-223 Package
LM2937-2.5, LM2937-3.3
www.national.com9
Physical Dimensions inches (millimeters) unless otherwise noted
Plastic Package
Order Number LM2937ET-2.5,
LM2937ET-3.3,
NS Package Number T03B
TO-263 3-Lead Plastic Surface Mount Package
Order Number LM2937ES-2.5, LM2937ES-3.3,
NS Package Number TS3B
LM2937-2.5, LM2937-3.3
www.national.com 10
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
SOT-223 3-Lead Plastic Surface Mount Package
Order Number LM2937IMP-2.5, LM2937IMP-3.3,
NS Package Number MA04A
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.
For the most current product information visit us at www.national.com.
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.
BANNED SUBSTANCE COMPLIANCE
National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products
Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain
no ‘‘Banned Substances’’ as defined in CSP-9-111S2.
Leadfree products are RoHS compliant.
National Semiconductor
Americas Customer
Support Center
Email: new.feedback@nsc.com
Tel: 1-800-272-9959
National Semiconductor
Europe Customer Support Center
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
Support Center
Email: ap.support@nsc.com
National Semiconductor
Japan Customer Support Center
Fax: 81-3-5639-7507
Email: jpn.feedback@nsc.com
Tel: 81-3-5639-7560
www.national.com
LM2937-2.5, LM2937-3.3 400mA and 500mA Voltage Regulators
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements,
and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should
obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are
sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment.
TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s standard
warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where
mandated by government requirements, testing of all parameters of each product is not necessarily performed.
TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and
applications using TI components. To minimize the risks associated with customer products and applications, customers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask work right,
or other TI intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information
published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a
warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual
property of the third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied
by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive
business practice. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional
restrictions.
Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service voids all
express and any implied warranties for the associated TI product or service and is an unfair and deceptive business practice. TI is not
responsible or liable for any such statements.
TI products are not authorized for use in safety-critical applications (such as life support) where a failure of the TI product would reasonably
be expected to cause severe personal injury or death, unless officers of the parties have executed an agreement specifically governing
such use. Buyers represent that they have all necessary expertise in the safety and regulatory ramifications of their applications, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products
and any use of TI products in such safety-critical applications, notwithstanding any applications-related information or support that may be
provided by TI. Further, Buyers must fully indemnify TI and its representatives against any damages arising out of the use of TI products in
such safety-critical applications.
TI products are neither designed nor intended for use in military/aerospace applications or environments unless the TI products are
specifically designated by TI as military-grade or "enhanced plastic."Only products designated by TI as military-grade meet military
specifications. Buyers acknowledge and agree that any such use of TI products which TI has not designated as military-grade is solely at
the Buyer's risk, and that they are solely responsible for compliance with all legal and regulatory requirements in connection with such use.
TI products are neither designed nor intended for use in automotive applications or environments unless the specific TI products are
designated by TI as compliant with ISO/TS 16949 requirements. Buyers acknowledge and agree that, if they use any non-designated
products in automotive applications, TI will not be responsible for any failure to meet such requirements.
Following are URLs where you can obtain information on other Texas Instruments products and application solutions:
Products Applications
Audio www.ti.com/audio Communications and Telecom www.ti.com/communications
Amplifiers amplifier.ti.com Computers and Peripherals www.ti.com/computers
Data Converters dataconverter.ti.com Consumer Electronics www.ti.com/consumer-apps
DLP®Products www.dlp.com Energy and Lighting www.ti.com/energy
DSP dsp.ti.com Industrial www.ti.com/industrial
Clocks and Timers www.ti.com/clocks Medical www.ti.com/medical
Interface interface.ti.com Security www.ti.com/security
Logic logic.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense
Power Mgmt power.ti.com Transportation and Automotive www.ti.com/automotive
Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video
RFID www.ti-rfid.com
OMAP Mobile Processors www.ti.com/omap
Wireless Connectivity www.ti.com/wirelessconnectivity
TI E2E Community Home Page e2e.ti.com
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright ©2011, Texas Instruments Incorporated
