National Semiconductor LM2596 Technical data

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LM2596
SIMPLE SWITCHER

®

Power Converter 150 kHz

3A Step-Down Voltage Regulator

LM2596 SIMPLE SWITCHER Power Converter 150 kHz 3A Step-Down Voltage Regulator

May 2002

General Description

The LM2596 series of regulators are monolithic integrated
circuits that provide all the active functions for a step-down
(buck) switching regulator, capable of driving a 3A load with
excellent line and load regulation. These devices are avail­able in fixed output voltages of 3.3V, 5V, 12V, and an adjust­able output version.

Requiring aminimum number of external components, these
regulators are simple to use and include internal frequency
compensation

The LM2596 series operates at a switching frequency of
150 kHz thus allowing smaller sized filter components than
what would be needed with lower frequency switching regu­lators. Available in a standard 5-lead TO-220 package with
several different lead bend options, and a 5-lead TO-263
surface mount package.

A standard series of inductors are available from several
different manufacturers optimized for use with the LM2596
series. This feature greatly simplifies the design of
switch-mode power supplies.

Other features include a guaranteed
put voltage under specified input voltage and output load
conditions, and
shutdown is included, featuring typically 80 µA standby cur­rent. Self protection features include a two stage frequency
reducing current limit for the output switch and an over
temperature shutdown for complete protection under fault
conditions.

†

, and a fixed-frequency oscillator.

±

4% tolerance on out-

±

15% on the oscillator frequency. External

Features

n 3.3V, 5V, 12V, and adjustable output versions
n Adjustable version output voltage range, 1.2V to 37V

±

4% max over line and load conditions

n Available in TO-220 and TO-263 packages
n Guaranteed 3A output load current
n Input voltage range up to 40V
n Requires only 4 external components
n Excellent line and load regulation specifications
n 150 kHz fixed frequency internal oscillator
n TTL shutdown capability
n Low power standby mode, I
n High efficiency
n Uses readily available standard inductors
n Thermal shutdown and current limit protection

typically 80 µA

Q

Applications

n Simple high-efficiency step-down (buck) regulator
n On-card switching regulators
n Positive to negative converter

Note:†Patent Number 5,382,918.

Typical Application (Fixed Output Voltage

Versions)

01258301

SIMPLE SWITCHER®and

© 2002 National Semiconductor Corporation DS012583 www.national.com

Switchers Made Simple

®

are registered trademarks of National Semiconductor Corporation.

Connection Diagrams and Ordering Information

LM2596

Bent and Staggered Leads, Through Hole

Package

5-Lead TO-220 (T)

Surface Mount Package

5-Lead TO-263 (S)

Order Number LM2596T-3.3, LM2596T-5.0,

01258302

LM2596T-12 or LM2596T-ADJ

See NS Package Number T05D

Order Number LM2596S-3.3, LM2596S-5.0,

01258303

LM2596S-12 or LM2596S-ADJ

See NS Package Number TS5B

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LM2596

Absolute Maximum Ratings (Note 1)

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

Maximum Supply Voltage 45V
ON /OFF Pin Input Voltage
Feedback Pin Voltage −0.3 ≤ V ≤+25V
Output Voltage to Ground

(Steady State) −1V
Power Dissipation Internally limited
Storage Temperature Range −65˚C to +150˚C
ESD Susceptibility

−0.3 ≤ V ≤ +25V

Human Body Model (Note 2) 2 kV
Lead Temperature
S Package

Vapor Phase (60 sec.) +215˚C

Infrared (10 sec.) +245˚C
T Package (Soldering, 10 sec.) +260˚C
Maximum Junction Temperature +150˚C

Operating Conditions

Temperature Range −40˚C ≤ TJ≤ +125˚C
Supply Voltage 4.5V to 40V

LM2596-3.3
Electrical Characteristics

Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range

LM2596-3.3

Symbol Parameter Conditions

SYSTEM PARAMETERS (Note 5) Test Circuit

V

OUT

η Efficiency V

Output Voltage 4.75V ≤ VIN≤ 40V, 0.2A ≤ I

IN

= 12V, I

Figure 1

=3A 73 %

LOAD

≤ 3A 3.3 V

LOAD

Typ

(Note 3)

Limit

(Note 4)

3.168/3.135 V(min)

3.432/3.465 V(max)

(Limits)

Units

LM2596-5.0
Electrical Characteristics

Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range

LM2596-5.0

Symbol Parameter Conditions

SYSTEM PARAMETERS (Note 5) Test Circuit

V

OUT

η Efficiency V

Output Voltage 7V ≤ VIN≤ 40V, 0.2A ≤ I

IN

= 12V, I

Figure 1

=3A 80 %

LOAD

≤ 3A 5.0 V

LOAD

Typ

(Note 3)

Limit

(Note 4)

4.800/4.750 V(min)

5.200/5.250 V(max)

(Limits)

LM2596-12
Electrical Characteristics

Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range

LM2596-12

Symbol Parameter Conditions

SYSTEM PARAMETERS (Note 5) Test Circuit

V

OUT

η Efficiency V

Output Voltage 15V ≤ VIN≤ 40V, 0.2A ≤ I

IN

= 25V, I

Figure 1

=3A 90 %

LOAD

≤ 3A 12.0 V

LOAD

Typ

(Note 3)

Limit

(Note 4)

11.52/11.40 V(min)

12.48/12.60 V(max)

(Limits)

Units

Units

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LM2596-ADJ
Electrical Characteristics

LM2596

Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range

LM2596-ADJ

Symbol Parameter Conditions

SYSTEM PARAMETERS (Note 5) Test Circuit

V

FB

Feedback Voltage 4.5V ≤ VIN≤ 40V, 0.2A ≤ I

V

OUT

Figure 1

programmed for 3V. Circuit of

≤ 3A 1.230 V

LOAD

Figure 1

Typ

(Note 3)

Limit

(Note 4)

1.193/1.180 V(min)

1.267/1.280 V(max)

η Efficiency V

= 12V, V

IN

OUT

= 3V, I

=3A 73 %

LOAD

All Output Voltage Versions
Electrical Characteristics

Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range. Unless otherwise specified, V

sion. I

LOAD

= 500 mA

Symbol Parameter Conditions

DEVICE PARAMETERS

I

b

f

O

V

SAT

Feedback Bias Current Adjustable Version Only, VFB= 1.3V 10 nA

Oscillator Frequency (Note 6) 150 kHz

Saturation Voltage I

DC Max Duty Cycle (ON) (Note 8) 100 %

Min Duty Cycle (OFF) (Note 9) 0

I

CL

I

L

I

Q

I

STBY

θ

JC

θ

JA

θ

JA

θ

JA

θ

JA

ON/OFF CONTROL Test Circuit

Current Limit Peak Current (Notes 7, 8) 4.5 A

Output Leakage Current Output = 0V (Notes 7, 9) 50 µA(max)

Quiescent Current (Note 9) 5 mA

Standby Quiescent Current ON/OFF pin = 5V (OFF) (Note 10) 80 µA

Thermal Resistance TO-220 or TO-263 Package, Junction to Case 2 ˚C/W

Figure 1

ON /OFF Pin Logic Input 1.3 V

V

IH

V

IL

Threshold Voltage Low (Regulator ON) 0.6 V(max)

= 12V for the 3.3V, 5V, and Adjustable version and VIN= 24V for the 12V ver-

IN

LM2596-XX

Typ

(Note 3)

Limit

(Note 4)

50/100 nA (max)

127/110 kHz(min)
173/173 kHz(max)

= 3A (Notes 7, 8) 1.16 V

OUT

1.4/1.5 V(max)

3.6/3.4 A(min)

6.9/7.5 A(max)

Output = −1V (Note 10) 2 mA

30 mA(max)

10 mA(max)

200/250 µA(max)

TO-220 Package, Junction to Ambient (Note 11) 50 ˚C/W
TO-263 Package, Junction to Ambient (Note 12) 50 ˚C/W
TO-263 Package, Junction to Ambient (Note 13) 30 ˚C/W
TO-263 Package, Junction to Ambient (Note 14) 20 ˚C/W

High (Regulator OFF) 2.0 V(min)

Units

(Limits)

Units

(Limits)

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All Output Voltage Versions
Electrical Characteristics

Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Tempera­ture Range. Unless otherwise specified, V

sion. I

Symbol Parameter Conditions

I

H

I

L

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: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin.
Note 3: Typical numbers are at 25˚C and represent the most likely norm.
Note 4: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%

production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to
calculate Average Outgoing Quality Level (AOQL).

Note 5: External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator
system performance.WhentheLM2596is used as shown in the
Characteristics.

Note 6: The switching frequency is reduced when the second stage current limit is activated.
Note 7: No diode, inductor or capacitor connected to output pin.
Note 8: Feedback pin removed from output and connected to 0V to force the output transistor switch ON.
Note 9: Feedback pin removed from output and connected to 12V for the 3.3V,5V, and theADJ. version, and 15V for the 12V version, to force the output transistor

switch OFF.

Note 10: V
Note 11: Junction to ambient thermal resistance (no external heat sink) for the TO-220 package mounted vertically, with the leads soldered to a printed circuit board

with (1 oz.) copper area of approximately 1 in

Note 12: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single printed circuit board with 0.5 in
Note 13: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 2.5 in
Note 14: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in

the LM2596S side of the board, and approximately 16 in
model in Switchers Made Simple

= 500 mA

LOAD

ON /OFF Pin Input Current V

= 40V.

IN

™

version 4.3 software.

2

.

(Continued)

= 12V for the 3.3V, 5V, and Adjustable version and VIN= 24V for the 12V ver-

IN

LM2596-XX

Typ

(Note 3)

= 2.5V (Regulator OFF) 5 µA

LOGIC

Limit

(Note 4)

15 µA(max)

V

= 0.5V (Regulator ON) 0.02 µA

LOGIC

5 µA(max)

Figure 1

test circuit, system performance will be as shown in system parameters section of Electrical

2

of (1 oz.) copper area.

2

of (1 oz.) copper area.

2

2

of copper on the other side of the p-c board. SeeApplication Information in this data sheet and the thermal

of (1 oz.) copper area on

Units

(Limits)

LM2596

Typical Performance Characteristics (Circuit of

Normalized

Output Voltage Line Regulation Efficiency

01258304

Figure 1

01258305

)

01258306

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Typical Performance Characteristics (Circuit of

Figure 1

) (Continued)

LM2596

Switch Saturation

Voltage Switch Current Limit Dropout Voltage

01258307 01258308

Operating

Quiescent Current

Shutdown

Quiescent Current

Minimum Operating

Supply Voltage

01258309

ON /OFF Threshold

Voltage

01258310 01258311

ON /OFF Pin

Current (Sinking) Switching Frequency

01258313

01258314

01258312

01258315

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LM2596

Typical Performance Characteristics (Circuit of

Feedback Pin

Bias Current

01258316

Figure 1

) (Continued)

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Typical Performance Characteristics

LM2596

Continuous Mode Switching Waveforms

V

= 20V, V

IN

L = 32 µH, C

OUT

= 5V, I

OUT

= 220 µF, C

=2A

LOAD

ESR=50mΩ

OUT

Discontinuous Mode Switching Waveforms

V

= 20V, V

IN

L = 10 µH, C

OUT

= 5V, I

OUT

= 330 µF, C

= 500 mA

LOAD

ESR=45mΩ

OUT

Horizontal Time Base: 2 µs/div.

01258317

A: Output Pin Voltage, 10V/div.
B: Inductor Current 1A/div.
C: Output Ripple Voltage, 50 mV/div.

Load Transient Response for Continuous Mode

V

= 20V, V

IN

L = 32 µH, C

= 5V, I

OUT

= 220 µF, C

OUT

= 500 mA to 2A

LOAD

OUT

ESR=50mΩ

01258319

Horizontal Time Base: 100 µs/div.

A: Output Voltage, 100 mV/div. (AC)
B: 500 mA to 2A Load Pulse

Test Circuit and Layout Guidelines

Horizontal Time Base: 2 µs/div.

A: Output Pin Voltage, 10V/div.
B: Inductor Current 0.5A/div.
C: Output Ripple Voltage, 100 mV/div.

Load Transient Response for Discontinuous Mode

V

= 20V, V

IN

L = 10 µH, C

= 5V, I

OUT

= 330 µF, C

OUT

= 500 mA to 2A

LOAD

OUT

ESR=45mΩ

Horizontal Time Base: 200 µs/div.

A: Output Voltage, 100 mV/div. (AC)
B: 500 mA to 2A Load Pulse

01258318

01258320

Fixed Output Voltage Versions

CIN—470 µF, 50V, Aluminum Electrolytic Nichicon “PL Series”
C

—220 µF, 25V Aluminum Electrolytic, Nichicon “PL Series”

OUT

D1 — 5A, 40V Schottky Rectifier, 1N5825
L1 — 68 µH, L38

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01258322

Test Circuit and Layout Guidelines (Continued)

Adjustable Output Voltage Versions

LM2596

01258323

where V

Select R1to be approximately 1 kΩ, use a 1% resistor for best stability.
C

IN

C

OUT

D1 — 5A, 40V Schottky Rectifier, 1N5825
L1 — 68 µH, L38
R1 — 1 kΩ,1%
C

FF

= 1.23V

REF

—470 µF, 50V, Aluminum Electrolytic Nichicon “PL Series”

—220 µF, 35V Aluminum Electrolytic, Nichicon “PL Series”

—See Application Information Section

FIGURE 1. Standard Test Circuits and Layout Guides

As in any switching regulator, layout is very important. Rap­idly switching currents associated with wiring inductance can
generate voltage transients which can cause problems. For
minimal inductance and ground loops, the wires indicated by

heavy lines should be wide printed circuit traces and
should be kept as short as possible. For best results,

external components should be located as close to the
switcher lC as possible using ground plane construction or
single point grounding.

If open core inductors are used, special care must be
taken as to the location and positioning of this type of induc­tor.Allowing the inductor flux to intersect sensitive feedback,
lC groundpath and C

wiring can cause problems.

OUT

When using the adjustable version, special care must be
taken as to the location of the feedback resistors and the
associated wiring. Physically locate both resistors near the
IC, and route the wiring away from the inductor, especially an
open core type of inductor. (See application section for more
information.)

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LM2596 Series Buck Regulator Design Procedure (Fixed Output)

LM2596

PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)

Given:

V

= Regulated Output Voltage (3.3V, 5V or 12V)

OUT

V

(max) = Maximum DC Input Voltage

IN

I

(max) = Maximum Load Current

LOAD

1. Inductor Selection (L1)
A. Select the correct inductor value selection guide from Fig-

ures

Figure 4,Figure 5

,or

Figure 6

. (Output voltages of 3.3V,
5V, or 12V respectively.)For all other voltages, see the design
procedure for the adjustable version.

B. From the inductor value selection guide, identify the induc­tance region intersected by the Maximum Input Voltage line
and the Maximum Load Current line. Each region is identified
by an inductance value and an inductor code (LXX).

C. Select an appropriate inductor from the four manufacturer’s
part numbers listed in

2. Output Capacitor Selection (C

Figure 8

.

)

OUT

A. In the majority of applications, low ESR (Equivalent Series

Resistance) electrolytic capacitors between 82 µF and 820 µF
and low ESR solid tantalum capacitors between 10 µF and
470 µF provide the best results. This capacitor should be
located close to the IC using short capacitor leads and short
copper traces. Do not use capacitors larger than 820 µF .

For additional information, see section on output capaci­tors in application information section.

B. To simplify the capacitor selection procedure, refer to the

quick design component selection table shown in

Figure 2

This table contains different input voltages, output voltages,
and load currents, and lists various inductors and output ca­pacitors that will provide the best design solutions.

C. The capacitor voltage rating for electrolytic capacitors
should be at least 1.5 times greater than the output voltage,
and often much higher voltage ratings are needed to satisfy
the low ESR requirements for low output ripple voltage.

D. For computer aided design software, see

™

Simple

version 4.3 or later.

Switchers Made

Given:

=5V

V

OUT

V

(max) = 12V

IN

I

(max) = 3A

LOAD

1. Inductor Selection (L1)
A. Use the inductor selection guide for the 5V version shown

Figure 5

in

.

B. From the inductor value selection guide shown in
the inductance region intersected by the 12V horizontal line
and the 3A vertical line is 33 µH, and the inductor code is L40.

C. The inductance value required is 33 µH. From the table in

Figure 8

, go to the L40 line and choose an inductor part
number from any of the four manufacturers shown. (In most
instance, both through hole and surface mount inductors are
available.)

2. Output Capacitor Selection (C
A. See section on output capacitors in application infor-

mation section.
B. From the quick design component selection table shown in

Figure 2

, locate the 5V output voltage section. In the load
current column, choose the load current line that is closest to
the current needed in your application, for this example, use
the 3A line. In the maximum input voltage column, select the
line that covers the input voltage needed in your application, in
this example, use the 15V line. Continuing on this line are
recommended inductors and capacitors that will provide the

.

best overall performance.
The capacitor list contains both through hole electrolytic and

surface mount tantalum capacitors from four different capaci­tor manufacturers. It is recommended that both the manufac­turers and the manufacturer’s series that are listed in the table
be used.

In this example aluminum electrolytic capacitors from several
different manufacturers are available with the range of ESR
numbers needed.

330 µF 35V Panasonic HFQ Series
330 µF 35V Nichicon PL Series

C. For a 5V output, a capacitor voltage rating at least 7.5V or
more is needed. But even a low ESR, switching grade, 220 µF
10V aluminum electrolytic capacitor would exhibit approxi­mately 225 mΩ of ESR (see the curve in
vs voltage rating). This amount of ESR would result in rela­tively high output ripple voltage. To reduce the ripple to 1% of
the output voltage, or less, a capacitor with a higher value or
with a higher voltage rating (lower ESR) should be selected. A
16V or 25V capacitor will reduce the ripple voltage by approxi­mately half.

OUT

)

Figure 14

Figure 5

for the ESR

,

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