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LM2596

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SNVS124C –NOVEMBER 1999–REVISED APRIL 2013

®

LM2596 SIMPLE SWITCHER Power Converter 150 kHz

3A Step-Down Voltage Regulator

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1

FEATURES

DESCRIPTION

The LM2596 series of regulators are monolithic

23

•

3.3V, 5V, 12V, and Adjustable Output Versions

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.

•

Adjustable Version Output Voltage Range,

1.2V to 37V ±4% Max Over Line and Load

Conditions

•

Available in TO-220 and TO-263 Packages

Ensured 3A Output Load Current

Input Voltage Range Up to 40V

Requiring

a

minimum number of external

components, these regulators are simple to use and

include internal frequency compensation , and a

fixed-frequency oscillator.

Requires Only 4 External Components

Excellent Line and Load Regulation

Specifications

The LM2596 series operates at a switching frequency

of 150 kHz thus allowing smaller sized filter

components than what would be needed with lower

•

150 kHz Fixed Frequency Internal Oscillator

TTL Shutdown Capability

frequency switching regulators. Available in

a

Low Power Standby Mode, I_QTypically 80 μA

High Efficiency

standard 5-lead TO-220 package with several

different lead bend options, and a 5-lead TO-263

surface mount package.

Uses Readily Available Standard Inductors

Thermal Shutdown and Current Limit

Protection

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.

APPLICATIONS

•

Simple High-Efficiency Step-Down (Buck)

Regulator

Other features include a ensured ±4% tolerance on

output voltage under specified input voltage and

output load conditions, and ±15% on the oscillator

frequency. External 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

•

On-Card Switching Regulators

Positive to Negative Converter

(1)

fault conditions.

(1) † Patent Number 5,382,918.

Typical Application

(Fixed Output Voltage Versions)

1

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

SIMPLE SWITCHER is a registered trademark of Texas Instruments.

2

3

All other trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

LM2596

SNVS124C –NOVEMBER 1999–REVISED APRIL 2013

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Connection Diagrams

Figure 1. 5-Lead Bent and Staggered Leads,

Through Hole TO-220 (T) Package

See Package Number NDH0005D

Figure 2. 5-Lead DDPAK/TO-263 (S) Package

See Package Number KTT0005B

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

(1)(2)

Absolute Maximum Ratings

Maximum Supply Voltage

ON /OFF Pin Input Voltage

Feedback Pin Voltage

45V

−0.3 ≤ V ≤ +25V

−0.3 ≤ V ≤+25V

−1V

Output Voltage to Ground (Steady State)

Power Dissipation

Internally limited

−65°C to +150°C

Storage Temperature Range

ESD Susceptibility

(3)

Human Body Model

2 kV

Lead Temperature

DDPAK/TO-263 Package

Vapor Phase (60 sec.)

+215°C

+245°C

+260°C

+150°C

Infrared (10 sec.)

TO-220 Package (Soldering, 10 sec.)

Maximum Junction Temperature

(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 ensure specific performance limits. For ensured specifications and test

conditions, see the Electrical Characteristics.

(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and

specifications.

(3) The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin.

Operating Conditions

Temperature Range

−40°C ≤ T_J≤ +125°C

Supply Voltage

4.5V to 40V

2

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LM2596-3.3 Electrical Characteristics

Specifications with standard type face are for T_J= 25°C, and those with boldface type apply over full Operating

Temperature Range

LM2596-3.3

Units

(Limits)

Symbol

Parameter

Conditions

Typ

Limit

(1)

(2)

SYSTEM PARAMETERS ⁽³⁾Test Circuit Figure 20

V_OUT

Output Voltage

4.75V ≤ V_IN≤ 40V, 0.2A ≤ I_LOAD≤ 3A

3.3

73

V

3.168/3.135

3.432/3.465

V(min)

V(max)

%

η

Efficiency

V_IN= 12V, I_LOAD= 3A

(1) Typical numbers are at 25°C and represent the most likely norm.

(2) All limits specified 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 ensured via correlation using standard Statistical Quality Control

(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

(3) External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect

switching regulator system performance. When the LM2596 is used as shown in the Figure 20 test circuit, system performance will be

as shown in system parameters of Electrical Characteristics section.

LM2596-5.0 Electrical Characteristics

Specifications with standard type face are for T_J= 25°C, and those with boldface type apply over full Operating

Temperature Range

LM2596-5.0

Units

Symbol

Parameter

Conditions

Typ

Limit

(Limits)

(1)

(2)

SYSTEM PARAMETERS ⁽³⁾Test Circuit Figure 20

V_OUT

Output Voltage

7V ≤ V_IN≤ 40V, 0.2A ≤ I_LOAD≤ 3A

5.0

80

V

4.800/4.750

5.200/5.250

V(min)

V(max)

%

η

Efficiency

V_IN= 12V, I_LOAD= 3A

(1) Typical numbers are at 25°C and represent the most likely norm.

(2) All limits specified 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 ensured via correlation using standard Statistical Quality Control

(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

(3) External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect

switching regulator system performance. When the LM2596 is used as shown in the Figure 20 test circuit, system performance will be

as shown in system parameters of Electrical Characteristics section.

LM2596-12 Electrical Characteristics

Specifications with standard type face are for T_J= 25°C, and those with boldface type apply over full Operating

Temperature Range

LM2596-12

Units

Symbol

Parameter

Conditions

Typ

Limit

(Limits)

(1)

(2)

SYSTEM PARAMETERS ⁽³⁾Test Circuit Figure 20

V_OUT

Output Voltage

15V ≤ V_IN≤ 40V, 0.2A ≤ I_LOAD≤ 3A

12.0

90

V

11.52/11.40

12.48/12.60

V(min)

V(max)

%

η

Efficiency

V_IN= 25V, I_LOAD= 3A

(1) Typical numbers are at 25°C and represent the most likely norm.

(2) All limits specified 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 ensured via correlation using standard Statistical Quality Control

(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

(3) External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect

switching regulator system performance. When the LM2596 is used as shown in the Figure 20 test circuit, system performance will be

as shown in system parameters of Electrical Characteristics section.

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LM2596-ADJ Electrical Characteristics

Specifications with standard type face are for T_J= 25°C, and those with boldface type apply over full Operating

Temperature Range

LM2596-ADJ

Units

(Limits)

Symbol

Parameter

Conditions

Typ

Limit

(1)

(2)

SYSTEM PARAMETERS ⁽³⁾Test Circuit Figure 20

V_FB

Feedback Voltage

4.5V ≤ V_IN≤ 40V, 0.2A ≤ I_LOAD≤ 3A

1.230

73

V

V_OUTprogrammed for 3V. Circuit of Figure 20

1.193/1.180

1.267/1.280

V(min)

V(max)

%

η

Efficiency

V_IN= 12V, V_OUT= 3V, I_LOAD= 3A

(1) Typical numbers are at 25°C and represent the most likely norm.

(2) All limits specified 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 ensured via correlation using standard Statistical Quality Control

(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

(3) External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect

switching regulator system performance. When the LM2596 is used as shown in the Figure 20 test circuit, system performance will be

as shown in system parameters of Electrical Characteristics section.

All Output Voltage Versions Electrical Characteristics

Specifications with standard type face are for T_J= 25°C, and those with boldface type apply over full Operating

Temperature Range. Unless otherwise specified, V_IN= 12V for the 3.3V, 5V, and Adjustable version and V_IN= 24V for the

12V version. I_LOAD= 500 mA

LM2596-XX

Units

Symbol

Parameter

Conditions

Typ

Limit

(Limits)

(1)

(2)

DEVICE PARAMETERS

I_b

Feedback Bias Current

Adjustable Version Only, V_FB= 1.3V

10

nA

nA (max)

kHz

50/100

(3)

f_O

Oscillator Frequency

Saturation Voltage

See

150

127/110

173/173

kHz(min)

kHz(max)

V

(4) (5)

V_SAT

DC

I_OUT= 3A

1.16

1.4/1.5

V(max)

%

(5)

Max Duty Cycle (ON)

Min Duty Cycle (OFF)

Current Limit

See

100

0

(6)

See

(4)(5)

I_CL

Peak Current

4.5

A

3.6/3.4

6.9/7.5

50

A(min)

A(max)

μA(max)

mA

(4)(6)

I_L

Output Leakage Current

Quiescent Current

Output = 0V

(7)

Output = −1V

2

5

30

10

mA(max)

mA

(6)

I_Q

See

mA(max)

(1) Typical numbers are at 25°C and represent the most likely norm.

(2) All limits specified 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 ensured via correlation using standard Statistical Quality Control

(SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

(3) The switching frequency is reduced when the second stage current limit is activated.

(4) No diode, inductor or capacitor connected to output pin.

(5) Feedback pin removed from output and connected to 0V to force the output transistor switch ON.

(6) Feedback pin removed from output and connected to 12V for the 3.3V, 5V, and the ADJ. version, and 15V for the 12V version, to force

the output transistor switch OFF.

(7) V_IN= 40V.

4

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All Output Voltage Versions Electrical Characteristics (continued)

Specifications with standard type face are for T_J= 25°C, and those with boldface type apply over full Operating

Temperature Range. Unless otherwise specified, V_IN= 12V for the 3.3V, 5V, and Adjustable version and V_IN= 24V for the

12V version. I_LOAD= 500 mA

LM2596-XX

Units

Symbol

I_STBY

Parameter

Conditions

Typ

Limit

(Limits)

(1)

(2)

(7)

Standby Quiescent Current

ON/OFF pin = 5V (OFF)

80

μA

μA(max)

°C/W

200/250

θ_JC

θ_JA

Thermal Resistance

TO-220 or TO-263 Package, Junction to Case

2

(8)

TO-220 Package, Junction to Ambient

50

30

20

(9)

TO-263 Package, Junction to Ambient

(10)

TO-263 Package, Junction to Ambient

(11)

TO-263 Package, Junction to Ambient

ON/OFF CONTROL Test Circuit Figure 20

ON /OFF Pin Logic Input

1.3

V

V_IH

V_IL

I_H

Threshold Voltage

Low (Regulator ON)

0.6

2.0

V(max)

V(min)

μA

High (Regulator OFF)

ON /OFF Pin Input Current

V_LOGIC= 2.5V (Regulator OFF)

5

15

5

μA(max)

μA

I_L

V_LOGIC= 0.5V (Regulator ON)

0.02

μA(max)

(8) 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 in².

(9) Junction to ambient thermal resistance with the TO-263 package tab soldered to a single printed circuit board with 0.5 in²of (1 oz.)

copper area.

(10) Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 2.5 in²of (1

oz.) copper area.

(11) Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in²of (1 oz.)

copper area on the LM2596S side of the board, and approximately 16 in²of copper on the other side of the p-c board. See Application

Information in this data sheet and the thermal model in Switchers Made Simple™ version 4.3 software.

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Typical Performance Characteristics

(Circuit of Figure 20)

Normalized

Output Voltage

Line Regulation

Figure 3.

Figure 4.

Switch Saturation

Voltage

Efficiency

Figure 5.

Figure 6.

Switch Current Limit

Dropout Voltage

Figure 7.

Figure 8.

6

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Typical Performance Characteristics (continued)

(Circuit of Figure 20)

Operating

Quiescent Current

Shutdown

Quiescent Current

Figure 9.

Figure 10.

Minimum Operating

Supply Voltage

ON /OFF Threshold

Voltage

Figure 11.

Figure 12.

ON /OFF Pin

Current (Sinking)

Switching Frequency

Figure 13.

Figure 14.

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Typical Performance Characteristics (continued)

(Circuit of Figure 20)

Continuous Mode Switching Waveforms

Feedback Pin

Bias Current

V_IN= 20V, V_OUT= 5V, I_LOAD= 2A

L = 32 μH, C_OUT= 220 μF, C_OUTESR = 50 mΩ

A: Output Pin Voltage, 10V/div.

B: Inductor Current 1A/div.

C: Output Ripple Voltage, 50 mV/div.

Figure 15.

Figure 16. Horizontal Time Base: 2 μs/div.

Discontinuous Mode Switching Waveforms

V_IN= 20V, V_OUT= 5V, I_LOAD= 500 mA

L = 10 μH, C_OUT= 330 μF, C_OUTESR = 45 mΩ

Load Transient Response for Continuous Mode

V_IN= 20V, V_OUT= 5V, I_LOAD= 500 mA to 2A

L = 32 μH, C_OUT= 220 μF, C_OUTESR = 50 mΩ

A: Output Voltage, 100 mV/div. (AC)

B: 500 mA to 2A Load Pulse

A: Output Pin Voltage, 10V/div.

B: Inductor Current 0.5A/div.

C: Output Ripple Voltage, 100 mV/div.

Figure 17. Horizontal Time Base: 2 μs/div.

Figure 18. Horizontal Time Base: 100 μs/div.

Load Transient Response for Discontinuous Mode

V_IN= 20V, V_OUT= 5V, I_LOAD= 500 mA to 2A

L = 10 μH, C_OUT= 330 μF, C_OUTESR = 45 mΩ

A: Output Voltage, 100 mV/div. (AC)

B: 500 mA to 2A Load Pulse

Figure 19. Horizontal Time Base: 200 μs/div.

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Test Circuit and Layout Guidelines

Fixed Output Voltage Versions

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

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

D1 —5A, 40V Schottky Rectifier, 1N5825

L1 —68 μH, L38

Adjustable Output Voltage Versions

where V_REF= 1.23V

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

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

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

D1 —5A, 40V Schottky Rectifier, 1N5825

L1 —68 μH, L38

R1 —1 kΩ, 1%

C_FF—See Application Information Section

Figure 20. 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_OUTwiring can cause

problems.

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 Information section for more information.)

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LM2596 Series Buck Regulator Design Procedure (Fixed Output)

PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

Given:

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

V_IN(max) = Maximum DC Input Voltage

I_LOAD(max) = Maximum Load Current

V_OUT= 5V

V_IN(max) = 12V

I_LOAD(max) = 3A

1. Inductor Selection (L1)

A. Select the correct inductor value selection guide from Figures A. Use the inductor selection guide for the 5V version shown in

Figure 21, Figure 22, or Figure 23. (Output voltages of 3.3V, 5V, or Figure 22.

12V respectively.) For all other voltages, see the Design Procedure

for the adjustable version.

B. From the inductor value selection guide shown in Figure 22, the

inductance region intersected by the 12V horizontal line and the 3A

B. From the inductor value selection guide, identify the inductance vertical line is 33 μH, and the inductor code is L40.

region intersected by the Maximum Input Voltage line and the

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

Maximum Load Current line. Each region is identified by an

Table 3, go to the L40 line and choose an inductor part number from

inductance value and an inductor code (LXX).

any of the four manufacturers shown. (In most instance, both

C. Select an appropriate inductor from the four manufacturer's part through hole and surface mount inductors are available.)

numbers listed in Table 3.

2. Output Capacitor Selection (C_OUT

)

2. Output Capacitor Selection (C_OUT)

A. In the majority of applications, low ESR (Equivalent Series A. See section on output capacitors in Application Information

Resistance) electrolytic capacitors between 82 μF and 820 μF and section.

low ESR solid tantalum capacitors between 10 μF and 470 μF

B. From the quick design component selection table shown in

provide the best results. This capacitor should be located close to

Table 1, locate the 5V output voltage section. In the load current

the IC using short capacitor leads and short copper traces. Do not

column, choose the load current line that is closest to the current

use capacitors larger than 820 μF .

needed in your application, for this example, use the 3A line. In the

For additional information, see section on output capacitors in maximum input voltage column, select the line that covers the input

Application Information section.

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.

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

design component selection table shown in Table 1. This table

contains different input voltages, output voltages, and load currents, The capacitor list contains both through hole electrolytic and surface

and lists various inductors and output capacitors that will provide the mount tantalum capacitors from four different capacitor

best design solutions.

manufacturers. It is recommended that both the manufacturers and

the manufacturer's series that are listed in the table be used.

C. The capacitor voltage rating for electrolytic capacitors should be

at least 1.5 times greater than the output voltage, and often much In this example aluminum electrolytic capacitors from several

higher voltage ratings are needed to satisfy the low ESR different manufacturers are available with the range of ESR numbers

requirements for low output ripple voltage.

needed.

D. For computer aided design software, see Switchers Made

330 μF 35V Panasonic HFQ Series

Simple™ version 4.3 or later.

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 Figure 26 for the ESR 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.

10

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PROCEDURE (Fixed Output Voltage Version)

3. Catch Diode Selection (D1)

EXAMPLE (Fixed Output Voltage Version)

3. Catch Diode Selection (D1)

A. The catch diode current rating must be at least 1.3 times greater A. Refer to the table shown in Table 6. In this example, a 5A, 20V,

than the maximum load current. Also, if the power supply design 1N5823 Schottky diode will provide the best performance, and will

must withstand a continuous output short, the diode should have a not be overstressed even for a shorted output.

current rating equal to the maximum current limit of the LM2596. The

most stressful condition for this diode is an overload or shorted

output condition.

B. The reverse voltage rating of the diode should be at least 1.25

times the maximum input voltage.

C. This diode must be fast (short reverse recovery time) and must be

located close to the LM2596 using short leads and short printed

circuit traces. Because of their fast switching speed and low forward

voltage drop, Schottky diodes provide the best performance and

efficiency, and should be the first choice, especially in low output

voltage applications. Ultra-fast recovery, or High-Efficiency rectifiers

also provide good results. Ultra-fast recovery diodes typically have

reverse recovery times of 50 ns or less. Rectifiers such as the

1N5400 series are much too slow and should not be used.

4. Input Capacitor (C_IN

)

4. Input Capacitor (C_IN)

A low ESR aluminum or tantalum bypass capacitor is needed The important parameters for the Input capacitor are the input

between the input pin and ground pin to prevent large voltage voltage rating and the RMS current rating. With a nominal input

transients from appearing at the input. This capacitor should be voltage of 12V, an aluminum electrolytic capacitor with a voltage

located close to the IC using short leads. In addition, the RMS rating greater than 18V (1.5 × V_IN) would be needed. The next

current rating of the input capacitor should be selected to be at least higher capacitor voltage rating is 25V.

½ the DC load current. The capacitor manufacturers data sheet must

The RMS current rating requirement for the input capacitor in a buck

be checked to assure that this current rating is not exceeded. The

regulator is approximately ½ the DC load current. In this example,

curve shown in Figure 25 shows typical RMS current ratings for

with a 3A load, a capacitor with a RMS current rating of at least 1.5A

several different aluminum electrolytic capacitor values.

is needed. The curves shown in Figure 25 can be used to select an

For an aluminum electrolytic, the capacitor voltage rating should be appropriate input capacitor. From the curves, locate the 35V line and

approximately 1.5 times the maximum input voltage. Caution must note which capacitor values have RMS current ratings greater than

be exercised if solid tantalum capacitors are used (see Application 1.5A. A 680 μF/35V capacitor could be used.

Information on input capacitor). The tantalum capacitor voltage rating

For a through hole design, a 680 μF/35V electrolytic capacitor

should be 2 times the maximum input voltage and it is recommended

(Panasonic HFQ series or Nichicon PL series or equivalent) would

that they be surge current tested by the manufacturer.

be adequate. other types or other manufacturers capacitors can be

Use caution when using ceramic capacitors for input bypassing, used provided the RMS ripple current ratings are adequate.

because it may cause severe ringing at the V_INpin.

For surface mount designs, solid tantalum capacitors can be used,

For additional information, see section on input capacitors in but caution must be exercised with regard to the capacitor surge

Application Information section.

current rating (see Application Information on input capacitors in this

data sheet). The TPS series available from AVX, and the 593D

series from Sprague are both surge current tested.

Table 1. LM2596 Fixed Voltage Quick Design Component Selection Table

Conditions

Inductor

Output Capacitor

Through Hole Electrolytic

Surface Mount Tantalum

Output

Voltage

(V)

Load

Current

(A)

Max Input

Voltage

(V)

Panasonic

HFQ Series

(μF/V)

Nichicon

PL Series

(μF/V)

AVX TPS

Series

(μF/V)

Sprague

595D Series

(μF/V)

Inductance

(μH)

Inductor

(#)

3.3

3

5

7

22 L41

470/25

560/35

680/35

560/35

470/25

330/35

560/16

560/35

680/35

470/35

330/35

270/50

330/6.3

220/10

390/6.3

330/10

22 L41

33 L40

22 L33

33 L32

47 L39

10

40

6

2

10

40

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Table 1. LM2596 Fixed Voltage Quick Design Component Selection Table (continued)

Conditions

Inductor

Output Capacitor

Through Hole Electrolytic Surface Mount Tantalum

Output

Voltage

(V)

Load

Current

(A)

Max Input

Voltage

(V)

Panasonic

HFQ Series

(μF/V)

Nichicon

PL Series

(μF/V)

AVX TPS

Series

(μF/V)

Sprague

595D Series

(μF/V)

Inductance

(μH)

Inductor

(#)

5

3

8

22 L41

470/25

560/25

330/35

470/25

180/35

470/25

330/25

180/25

180/35

330/25

180/25

82/25

560/16

560/25

330/35

270/35

560/16

180/35

470/25

330/25

180/25

180/35

330/25

180/25

82/25

220/10

100/10

100/16

68/20

330/10

270/10

180/16

120/20

180/16

120/20

68/25

10

15

40

9

22 L41

33 L40

47 L39

22 L33

68 L38

22 L41

33 L40

68 L44

33 L32

68 L38

150 L42

2

3

20

40

15

18

30

40

15

20

40

12

2

LM2596 Series Buck Regulator Design Procedure (Adjustable Output)

PROCEDURE (Adjustable Output Voltage Version)

EXAMPLE (Adjustable Output Voltage Version)

Given:

V_OUT= Regulated Output Voltage

V_OUT= 20V

V_IN(max) = Maximum Input Voltage

V_IN(max) = 28V

I_LOAD(max) = Maximum Load Current

F = Switching Frequency (Fixed at a nominal 150 kHz).

I_LOAD(max) = 3A

F = Switching Frequency (Fixed at a nominal 150 kHz).

1. Programming Output Voltage (Selecting R₁and R₂, as shown in 1. Programming Output Voltage (Selecting R₁and R₂, as shown in

Figure 20 )

Use the following formula to select the appropriate resistor values.

Select R₁to be 1 kΩ, 1%. Solve for R₂.

(3)

(1)

R₂= 1k (16.26 − 1) = 15.26k, closest 1% value is 15.4 kΩ.

R₂= 15.4 kΩ.

Select a value for R₁between 240Ω and 1.5 kΩ. The lower resistor

values minimize noise pickup in the sensitive feedback pin. (For the

lowest temperature coefficient and the best stability with time, use

1% metal film resistors.)

(2)

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PROCEDURE (Adjustable Output Voltage Version)

2. Inductor Selection (L1)

EXAMPLE (Adjustable Output Voltage Version)

2. Inductor Selection (L1)

A. Calculate the inductor Volt • microsecond constant E • T (V • μs), A. Calculate the inductor Volt • microsecond constant

from the following formula:

(E • T),

where

(5)

•

V_SAT= internal switch saturation voltage =

1.16V

B. E • T = 34.2 (V • μs)

C. I_LOAD(max) = 3A

•

V_D= diode forward voltage drop = 0.5V

(4)

D. From the inductor value selection guide shown in Figure 24, the

inductance region intersected by the 34 (V • μs) horizontal line and

the 3A vertical line is 47 μH, and the inductor code is L39.

B. Use the E • T value from the previous formula and match it with

the E • T number on the vertical axis of the Inductor Value Selection

Guide shown in Figure 24.

E. From the table in Table 3, locate line L39, and select an inductor

part number from the list of manufacturers part numbers.

C. on the horizontal axis, select the maximum load current.

D. Identify the inductance region intersected by the E • T value and

the Maximum Load Current value. Each region is identified by an

inductance value and an inductor code (LXX).

E. Select an appropriate inductor from the four manufacturer's part

numbers listed in Table 3.

3. Output Capacitor Selection (C_OUT

)

3. Output Capacitor SeIection (C_OUT)

A. In the majority of applications, low ESR electrolytic or solid A. See section on C_OUTin Application Information section.

tantalum capacitors between 82 μF and 820 μF provide the best

B. From the quick design table shown in Table 2, locate the output

results. This capacitor should be located close to the IC using short

voltage column. From that column, locate the output voltage closest

capacitor leads and short copper traces. Do not use capacitors

to the output voltage in your application. In this example, select the

larger than 820 μF. For additional information, see section on

output capacitors in Application Information section.

24V line. Under the OUTPUT CAPACITOR section, select

a

capacitor from the list of through hole electrolytic or surface mount

B. To simplify the capacitor selection procedure, refer to the quick tantalum types from four different capacitor manufacturers. It is

design table shown in Table 2. This table contains different output recommended that both the manufacturers and the manufacturers

voltages, and lists various output capacitors that will provide the best series that are listed in the table be used.

design solutions.

In this example, through hole aluminum electrolytic capacitors from

C. The capacitor voltage rating should be at least 1.5 times greater several different manufacturers are available.

than the output voltage, and often much higher voltage ratings are

needed to satisfy the low ESR requirements needed for low output

ripple voltage.

220 μF/35V Panasonic HFQ Series

150 μF/35V Nichicon PL Series

C. For a 20V output, a capacitor rating of at least 30V or more is

needed. In this example, either a 35V or 50V capacitor would work.

A 35V rating was chosen, although a 50V rating could also be used

if a lower output ripple voltage is needed.

Other manufacturers or other types of capacitors may also be used,

provided the capacitor specifications (especially the 100 kHz ESR)

closely match the types listed in the table. Refer to the capacitor

manufacturers data sheet for this information.

4. Feedforward Capacitor (C_FF) (See Figure 20)

4. Feedforward Capacitor (C_FF)

For output voltages greater than approximately 10V, an additional The table shown in Table 2 contains feed forward capacitor values

capacitor is required. The compensation capacitor is typically for various output voltages. In this example, a 560 pF capacitor is

between 100 pF and 33 nF, and is wired in parallel with the output needed.

voltage setting resistor, R₂. It provides additional stability for high

output voltages, low input-output voltages, and/or very low ESR

output capacitors, such as solid tantalum capacitors.

(6)

This capacitor type can be ceramic, plastic, silver mica, etc.

(Because of the unstable characteristics of ceramic capacitors made

with Z5U material, they are not recommended.)

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PROCEDURE (Adjustable Output Voltage Version)

5. Catch Diode Selection (D1)

EXAMPLE (Adjustable Output Voltage Version)

5. Catch Diode Selection (D1)

A. The catch diode current rating must be at least 1.3 times greater A. Refer to the table shown in Table 6. Schottky diodes provide the

than the maximum load current. Also, if the power supply design best performance, and in this example a 5A, 40V, 1N5825 Schottky

must withstand a continuous output short, the diode should have a diode would be a good choice. The 5A diode rating is more than

current rating equal to the maximum current limit of the LM2596. The adequate and will not be overstressed even for a shorted output.

most stressful condition for this diode is an overload or shorted

output condition.

B. The reverse voltage rating of the diode should be at least 1.25

times the maximum input voltage.

C. This diode must be fast (short reverse recovery time) and must be

located close to the LM2596 using short leads and short printed

circuit traces. Because of their fast switching speed and low forward

voltage drop, Schottky diodes provide the best performance and

efficiency, and should be the first choice, especially in low output

voltage applications. Ultra-fast recovery, or High-Efficiency rectifiers

are also a good choice, but some types with an abrupt turn-off

characteristic may cause instability or EMl problems. Ultra-fast

recovery diodes typically have reverse recovery times of 50 ns or

less. Rectifiers such as the 1N4001 series are much too slow and

should not be used.

6. Input Capacitor (C_IN

)

6. Input Capacitor (C_IN)

A low ESR aluminum or tantalum bypass capacitor is needed The important parameters for the Input capacitor are the input

between the input pin and ground to prevent large voltage transients voltage rating and the RMS current rating. With a nominal input

from appearing at the input. In addition, the RMS current rating of voltage of 28V, an aluminum electrolytic aluminum electrolytic

the input capacitor should be selected to be at least ½ the DC load capacitor with a voltage rating greater than 42V (1.5 × V_IN) would be

current. The capacitor manufacturers data sheet must be checked to needed. Since the the next higher capacitor voltage rating is 50V, a

assure that this current rating is not exceeded. The curve shown in 50V capacitor should be used. The capacitor voltage rating of (1.5 ×

Figure 25 shows typical RMS current ratings for several different V_IN) is a conservative guideline, and can be modified somewhat if

aluminum electrolytic capacitor values.

desired.

This capacitor should be located close to the IC using short leads The RMS current rating requirement for the input capacitor of a buck

and the voltage rating should be approximately 1.5 times the regulator is approximately ½ the DC load current. In this example,

maximum input voltage.

with a 3A load, a capacitor with a RMS current rating of at least 1.5A

is needed.

If solid tantalum input capacitors are used, it is recomended that they

be surge current tested by the manufacturer.

The curves shown in Figure 25 can be used to select an appropriate

input capacitor. From the curves, locate the 50V line and note which

capacitor values have RMS current ratings greater than 1.5A. Either

a 470 μF or 680 μF, 50V capacitor could be used.

Use caution when using a high dielectric constant ceramic capacitor

for input bypassing, because it may cause severe ringing at the V_IN

pin.

For a through hole design, a 680 μF/50V electrolytic capacitor

(Panasonic HFQ series or Nichicon PL series or equivalent) would

be adequate. Other types or other manufacturers capacitors can be

used provided the RMS ripple current ratings are adequate.

For additional information, see section on input capacitors in

Application Information section.

For surface mount designs, solid tantalum capacitors can be used,

but caution must be exercised with regard to the capacitor surge

current rting (see Application Information or input capacitors in this

data sheet). The TPS series available from AVX, and the 593D

series from Sprague are both surge current tested.

To further simplify the buck regulator design procedure, Texas

Instruments is making available computer design software to be

used with the Simple Switcher line ot switching regulators.

Switchers Made Simple (version 4.3 or later) is available on a 3½″

diskette for IBM compatible computers.

LM2596 Series Buck Regulator Design Procedure (Adjustable Output)

Table 2. Output Capacitor and Feedforward Capacitor Selection Table

Output

Voltage

(V)

Through Hole Output Capacitor

Surface Mount Output Capacitor

Panasonic

HFQ Series

(μF/V)

Nichicon PL

AVX TPS

Series

Sprague

595D Series

Feedforward

Capacitor

Feedforward

Capacitor

Series

(μF/V)

2

4

6

820/35

560/35

470/25

820/35

470/35

470/25

33 nF

10 nF

3.3 nF

330/6.3

220/10

470/4

390/6.3

330/10

33 nF

10 nF

3.3 nF

14

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Table 2. Output Capacitor and Feedforward Capacitor Selection Table (continued)

Output

Voltage

(V)

Through Hole Output Capacitor

Surface Mount Output Capacitor

Panasonic

HFQ Series

(μF/V)

Nichicon PL

AVX TPS

Series

Sprague

595D Series

Feedforward

Capacitor

Feedforward

Capacitor

Series

(μF/V)

9

330/25

220/35

100/50

330/25

220/35

150/35

100/50

1.5 nF

1 nF

100/16

68/20

33/25

10/35

180/16

120/20

33/25

1.5 nF

1 nF

1 2

1 5

2 4

2 8

680 pF

560 pF

390 pF

680 pF

220 pF

15/50

LM2596 Series Buck Regulator Design Procedure

INDUCTOR VALUE SELECTION GUIDES

(For Continuous Mode Operation)

Figure 21. LM2596-3.3

Figure 22. LM2596-5.0

Figure 23. LM2596-12

Figure 24. LM2596-ADJ

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Coilcraft

Table 3. Inductor Manufacturers Part Numbers

Inductance Current

Schott

Through

Hole

Renco

Through

Hole

Pulse Engineering

(μH)

(A)

Surface

Mount

Surface

Mount

Through

Hole

Surface

Mount

Surface

Mount

L15

L21

L22

L23

L24

L25

L26

L27

L28

L29

L30

L31

L32

L33

L34

L35

L36

L37

L38

L39

L40

L41

L42

L43

L44

22

68

0.99

1.17

1.40

1.70

2.10

0.80

1.00

1.20

1.47

1.78

2.20

2.50

3.10

3.40

1.70

2.10

2.50

3.10

3.50

2.70

3.40

67148350 67148460 RL-1284-22-43

67144070 67144450 RL-5471-5

67144080 67144460 RL-5471-6

67144090 67144470 RL-5471-7

67148370 67148480 RL-1283-22-43

67148380 67148490 RL-1283-15-43

67144100 67144480 RL-5471-1

67144110 67144490 RL-5471-2

67144120 67144500 RL-5471-3

67144130 67144510 RL-5471-4

67144140 67144520 RL-5471-5

67144150 67144530 RL-5471-6

67144160 67144540 RL-5471-7

67148390 67148500 RL-1283-22-43

67148400 67148790 RL-1283-15-43

RL1500-22 PE-53815

RL1500-68 PE-53821

PE-53815-S

PE-53821-S

PE-53822-S

PE-53823-S

PE-53825-S

PE-53824-S

PE-53826-S

PE-53827-S

PE-53828-S

PE-53829-S

PE-53830-S

PE-53831-S

PE-53932-S

PE-53933-S

PE-53934-S

PE-53935-S

PE-54036-S

PE-54037-S

PE-54038-S

PE-54039-S

PE-54040-S

PE-54041-S

PE-54042-S

DO3308-223

DO3316-683

DO3316-473

DO3316-333

DO3316-223

DO3316-153

DO5022P-334

DO5022P-224

DO5022P-154

DO5022P-104

DO5022P-683

DO5022P-473

DO5022P-333

DO5022P-223

DO5022P-153

—

47

—

PE-53822

PE-53823

PE-53824

PE-53825

PE-53826

PE-53827

PE-53828

PE-53829

PE-53830

PE-53831

PE-53932

PE-53933

PE-53934

PE-53935

PE-54036

PE-54037

PE-54038

PE-54039

PE-54040

PE-54041

PE-54042

PE-54043

PE-54044

33

22

15

330

220

150

100

68

47

33

22

15

220

150

100

68

67144170

67144180

67144190

67144200

67144210

—

RL-5473-1

RL-5473-4

RL-5472-1

RL-5472-2

RL-5472-3

—

47

—

33

67144220 67148290 RL-5472-4

67144230 67148300 RL-5472-5

—

22

—

150

100

68

67148410

67144240

67144250

—

RL-5473-4

RL-5473-2

RL-5473-3

—

Table 4. Inductor Manufacturers Phone Numbers

Coilcraft Inc.

Phone

FAX

(800) 322-2645

(708) 639-1469

+11 1236 730 595

+44 1236 730 627

(619) 674-8100

(619) 674-8262

+353 93 24 107

+353 93 24 459

(800) 645-5828

(516) 586-5562

(612) 475-1173

(612) 475-1786

Coilcraft Inc., Europe

Pulse Engineering Inc.

Phone

FAX

Phone

FAX

Pulse Engineering Inc., Europe

Renco Electronics Inc.

Schott Corp.

Phone

FAX

Phone

FAX

Phone

FAX

Table 5. Capacitor Manufacturers Phone Numbers

Nichicon Corp.

Panasonic

Phone

FAX

(708) 843-7500

(708) 843-2798

(714) 373-7857

(714) 373-7102

Phone

FAX

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Table 5. Capacitor Manufacturers Phone Numbers (continued)

AVX Corp.

Phone

FAX

(803) 448-9411

(803) 448-1943

(207) 324-4140

(207) 324-7223

Sprague/Vishay

Phone

FAX

Table 6. Diode Selection Table

VR

3A Diodes

4A–6A Diodes

Surface Mount

Schottky Ultra Fast

Through Hole

Surface Mount

Through Hole

Schottky

Ultra Fast

Schottky

Ultra Fast

Schottky

Ultra Fast

Recovery

20V

All of

these

diodes

are

rated to

at least

50V.

1N5820

SR302

All of

these

diodes

are

rated to

at least

50V.

All of

these

diodes

are

rated to

at least

50V.

SR502

1N5823

SB520

All of

these

diodes

are

rated to

at least

50V.

SK32

MBR320

1N5821

MBR330

31DQ03

1N5822

SR304

30V 30WQ03

SK33

50WQ03

50WQ04

SR503

1N5824

SB530

SR504

1N5825

SB540

40V SK34

MBRS340

30WQ04

MBR340

31DQ04

SR305

MURS320

30WF10

MUR320

MURS620

50WF10

MUR620

HER601

50V SK35

or

MBRS360

MBR350

31DQ05

50WQ05

SB550

More 30WQ05

50SQ080

Block Diagram

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APPLICATION INFORMATION

Table 7. PIN DESCRIPTIONS

Name

+V_IN

Description

This is the positive input supply for the IC switching regulator. A suitable input bypass

capacitor must be present at this pin to minimize voltage transients and to supply the

switching currents needed by the regulator.

Ground

Output

Feedback

Circuit ground.

Internal switch. The voltage at this pin switches between (+V_IN− V_SAT) and approximately

−0.5V, with a duty cycle of approximately V_OUT/V_IN. To minimize coupling to sensitive

circuitry, the PC board copper area connected to this pin should be kept to a minimum.

Senses the regulated output voltage to complete the feedback loop.

Allows the switching regulator circuit to be shut down using logic level signals thus dropping

the total input supply current to approximately 80 μA. Pulling this pin below a threshold

voltage of approximately 1.3V turns the regulator on, and pulling this pin above 1.3V (up to a

maximum of 25V) shuts the regulator down. If this shutdown feature is not needed, the ON

/OFF pin can be wired to the ground pin or it can be left open, in either case the regulator will

be in the ON condition.

ON /OFF

EXTERNAL COMPONENTS

INPUT CAPACITOR

C_IN— A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground pin. It

must be located near the regulator using short leads. This capacitor prevents large voltage transients from

appearing at the input, and provides the instantaneous current needed each time the switch turns on.

The important parameters for the Input capacitor are the voltage rating and the RMS current rating. Because of

the relatively high RMS currents flowing in a buck regulator's input capacitor, this capacitor should be chosen for

its RMS current rating rather than its capacitance or voltage ratings, although the capacitance value and voltage

rating are directly related to the RMS current rating.

The RMS current rating of a capacitor could be viewed as a capacitor's power rating. The RMS current flowing

through the capacitors internal ESR produces power which causes the internal temperature of the capacitor to

rise. The RMS current rating of a capacitor is determined by the amount of current required to raise the internal

temperature approximately 10°C above an ambient temperature of 105°C. The ability of the capacitor to dissipate

this heat to the surrounding air will determine the amount of current the capacitor can safely sustain. Capacitors

that are physically large and have a large surface area will typically have higher RMS current ratings. For a given

capacitor value, a higher voltage electrolytic capacitor will be physically larger than a lower voltage capacitor, and

thus be able to dissipate more heat to the surrounding air, and therefore will have a higher RMS current rating.

The consequences of operating an electrolytic capacitor above the RMS current rating is a shortened operating

life. The higher temperature speeds up the evaporation of the capacitor's electrolyte, resulting in eventual failure.

Selecting an input capacitor requires consulting the manufacturers data sheet for maximum allowable RMS ripple

current. For a maximum ambient temperature of 40°C, a general guideline would be to select a capacitor with a

ripple current rating of approximately 50% of the DC load current. For ambient temperatures up to 70°C, a

current rating of 75% of the DC load current would be a good choice for a conservative design. The capacitor

voltage rating must be at least 1.25 times greater than the maximum input voltage, and often a much higher

voltage capacitor is needed to satisfy the RMS current requirements.

A graph shown in Figure 25 shows the relationship between an electrolytic capacitor value, its voltage rating, and

the RMS current it is rated for. These curves were obtained from the Nichicon “PL” series of low ESR, high

reliability electrolytic capacitors designed for switching regulator applications. Other capacitor manufacturers offer

similar types of capacitors, but always check the capacitor data sheet.

“Standard” electrolytic capacitors typically have much higher ESR numbers, lower RMS current ratings and

typically have a shorter operating lifetime.

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Because of their small size and excellent performance, surface mount solid tantalum capacitors are often used

for input bypassing, but several precautions must be observed. A small percentage of solid tantalum capacitors

can short if the inrush current rating is exceeded. This can happen at turn on when the input voltage is suddenly

applied, and of course, higher input voltages produce higher inrush currents. Several capacitor manufacturers do

a 100% surge current testing on their products to minimize this potential problem. If high turn on currents are

expected, it may be necessary to limit this current by adding either some resistance or inductance before the

tantalum capacitor, or select a higher voltage capacitor. As with aluminum electrolytic capacitors, the RMS ripple

current rating must be sized to the load current.

FEEDFORWARD CAPACITOR

(Adjustable Output Voltage Version)

C_FF— A Feedforward Capacitor C_FF, shown across R2 in Figure 20 is used when the ouput voltage is greater

than 10V or when C_OUThas a very low ESR. This capacitor adds lead compensation to the feedback loop and

increases the phase margin for better loop stability. For C_FFselection, see the Design Procedure section.

Figure 25. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical)

OUTPUT CAPACITOR

C_OUT— An output capacitor is required to filter the output and provide regulator loop stability. Low impedance or

low ESR Electrolytic or solid tantalum capacitors designed for switching regulator applications must be used.

When selecting an output capacitor, the important capacitor parameters are; the 100 kHz Equivalent Series

Resistance (ESR), the RMS ripple current rating, voltage rating, and capacitance value. For the output capacitor,

the ESR value is the most important parameter.

The output capacitor requires an ESR value that has an upper and lower limit. For low output ripple voltage, a

low ESR value is needed. This value is determined by the maximum allowable output ripple voltage, typically 1%

to 2% of the output voltage. But if the selected capacitor's ESR is extremely low, there is a possibility of an

unstable feedback loop, resulting in an oscillation at the output. Using the capacitors listed in the tables, or

similar types, will provide design solutions under all conditions.

If very low output ripple voltage (less than 15 mV) is required, refer to the section on OUTPUT VOLTAGE

RIPPLE AND TRANSIENTS for a post ripple filter.

An aluminum electrolytic capacitor's ESR value is related to the capacitance value and its voltage rating. In most

cases, higher voltage electrolytic capacitors have lower ESR values (see Figure 26 ). Often, capacitors with

much higher voltage ratings may be needed to provide the low ESR values required for low output ripple voltage.

The output capacitor for many different switcher designs often can be satisfied with only three or four different

capacitor values and several different voltage ratings. See the quick design component selection tables in

Table 1 and 4 for typical capacitor values, voltage ratings, and manufacturers capacitor types.

Electrolytic capacitors are not recommended for temperatures below −25°C. The ESR rises dramatically at cold

temperatures and typically rises 3X @ −25°C and as much as 10X at −40°C. See curve shown in Figure 27.

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Solid tantalum capacitors have a much better ESR spec for cold temperatures and are recommended for

temperatures below −25°C.

Figure 26. Capacitor ESR vs Capacitor Voltage Rating (Typical Low ESR Electrolytic Capacitor)

CATCH DIODE

Buck regulators require a diode to provide a return path for the inductor current when the switch turns off. This

must be a fast diode and must be located close to the LM2596 using short leads and short printed circuit traces.

Because of their very fast switching speed and low forward voltage drop, Schottky diodes provide the best

performance, especially in low output voltage applications (5V and lower). Ultra-fast recovery, or High-Efficiency

rectifiers are also a good choice, but some types with an abrupt turnoff characteristic may cause instability or

EMI problems. Ultra-fast recovery diodes typically have reverse recovery times of 50 ns or less. Rectifiers such

as the 1N5400 series are much too slow and should not be used.

Figure 27. Capacitor ESR Change vs Temperature

INDUCTOR SELECTION

All switching regulators have two basic modes of operation; continuous and discontinuous. The difference

between the two types relates to the inductor current, whether it is flowing continuously, or if it drops to zero for a

period of time in the normal switching cycle. Each mode has distinctively different operating characteristics,

which can affect the regulators performance and requirements. Most switcher designs will operate in the

discontinuous mode when the load current is low.

The LM2596 (or any of the Simple Switcher family) can be used for both continuous or discontinuous modes of

operation.

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In many cases the preferred mode of operation is the continuous mode. It offers greater output power, lower

peak switch, inductor and diode currents, and can have lower output ripple voltage. But it does require larger

inductor values to keep the inductor current flowing continuously, especially at low output load currents and/or

high input voltages.

To simplify the inductor selection process, an inductor selection guide (nomograph) was designed (see Figure 21

through 8). This guide assumes that the regulator is operating in the continuous mode, and selects an inductor

that will allow a peak-to-peak inductor ripple current to be a certain percentage of the maximum design load

current. This peak-to-peak inductor ripple current percentage is not fixed, but is allowed to change as different

design load currents are selected. (See Figure 28.)

Figure 28. (ΔI_IND) Peak-to-Peak Inductor

Ripple Current (as a Percentage of the Load Current)

vs Load Current

By allowing the percentage of inductor ripple current to increase for low load currents, the inductor value and size

can be kept relatively low.

When operating in the continuous mode, the inductor current waveform ranges from a triangular to a sawtooth

type of waveform (depending on the input voltage), with the average value of this current waveform equal to the

DC output load current.

Inductors are available in different styles such as pot core, toroid, E-core, bobbin core, etc., as well as different

core materials, such as ferrites and powdered iron. The least expensive, the bobbin, rod or stick core, consists of

wire wound on a ferrite bobbin. This type of construction makes for an inexpensive inductor, but since the

magnetic flux is not completely contained within the core, it generates more Electro-Magnetic Interference (EMl).

This magnetic flux can induce voltages into nearby printed circuit traces, thus causing problems with both the

switching regulator operation and nearby sensitive circuitry, and can give incorrect scope readings because of

induced voltages in the scope probe. Also see section on OPEN CORE INDUCTORS.

When multiple switching regulators are located on the same PC board, open core magnetics can cause

interference between two or more of the regulator circuits, especially at high currents. A torroid or E-core inductor

(closed magnetic structure) should be used in these situations.

The inductors listed in the selection chart include ferrite E-core construction for Schott, ferrite bobbin core for

Renco and Coilcraft, and powdered iron toroid for Pulse Engineering.

Exceeding an inductor's maximum current rating may cause the inductor to overheat because of the copper wire

losses, or the core may saturate. If the inductor begins to saturate, the inductance decreases rapidly and the

inductor begins to look mainly resistive (the DC resistance of the winding). This can cause the switch current to

rise very rapidly and force the switch into a cycle-by-cycle current limit, thus reducing the DC output load current.

This can also result in overheating of the inductor and/or the LM2596. Different inductor types have different

saturation characteristics, and this should be kept in mind when selecting an inductor.

The inductor manufacturer's data sheets include current and energy limits to avoid inductor saturation.

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DISCONTINUOUS MODE OPERATION

The selection guide chooses inductor values suitable for continuous mode operation, but for low current

applications and/or high input voltages, a discontinuous mode design may be a better choice. It would use an

inductor that would be physically smaller, and would need only one half to one third the inductance value needed

for a continuous mode design. The peak switch and inductor currents will be higher in a discontinuous design,

but at these low load currents (1A and below), the maximum switch current will still be less than the switch

current limit.

Discontinuous operation can have voltage waveforms that are considerable different than a continuous design.

The output pin (switch) waveform can have some damped sinusoidal ringing present. (See Typical Performance

Characteristics photo titled Discontinuous Mode Switching Waveforms) This ringing is normal for discontinuous

operation, and is not caused by feedback loop instabilities. In discontinuous operation, there is a period of time

where neither the switch or the diode are conducting, and the inductor current has dropped to zero. During this

time, a small amount of energy can circulate between the inductor and the switch/diode parasitic capacitance

causing this characteristic ringing. Normally this ringing is not a problem, unless the amplitude becomes great

enough to exceed the input voltage, and even then, there is very little energy present to cause damage.

Different inductor types and/or core materials produce different amounts of this characteristic ringing. Ferrite core

inductors have very little core loss and therefore produce the most ringing. The higher core loss of powdered iron

inductors produce less ringing. If desired, a series RC could be placed in parallel with the inductor to dampen the

ringing. The computer aided design software Switchers Made Simple (version 4.3) will provide all component

values for continuous and discontinuous modes of operation.

Figure 29. Post Ripple Filter Waveform

OUTPUT VOLTAGE RIPPLE AND TRANSIENTS

The output voltage of a switching power supply operating in the continuous mode will contain a sawtooth ripple

voltage at the switcher frequency, and may also contain short voltage spikes at the peaks of the sawtooth

waveform.

The output ripple voltage is a function of the inductor sawtooth ripple current and the ESR of the output

capacitor. A typical output ripple voltage can range from approximately 0.5% to 3% of the output voltage. To

obtain low ripple voltage, the ESR of the output capacitor must be low, however, caution must be exercised when

using extremely low ESR capacitors because they can affect the loop stability, resulting in oscillation problems. If

very low output ripple voltage is needed (less than 20 mV), a post ripple filter is recommended. (See Figure 20.)

The inductance required is typically between 1 μH and 5 μH, with low DC resistance, to maintain good load

regulation. A low ESR output filter capacitor is also required to assure good dynamic load response and ripple

reduction. The ESR of this capacitor may be as low as desired, because it is out of the regulator feedback loop.

The photo shown in Figure 29 shows a typical output ripple voltage, with and without a post ripple filter.

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When observing output ripple with a scope, it is essential that a short, low inductance scope probe ground

connection be used. Most scope probe manufacturers provide a special probe terminator which is soldered onto

the regulator board, preferable at the output capacitor. This provides a very short scope ground thus eliminating

the problems associated with the 3 inch ground lead normally provided with the probe, and provides a much

cleaner and more accurate picture of the ripple voltage waveform.

The voltage spikes are caused by the fast switching action of the output switch and the diode, and the parasitic

inductance of the output filter capacitor, and its associated wiring. To minimize these voltage spikes, the output

capacitor should be designed for switching regulator applications, and the lead lengths must be kept very short.

Wiring inductance, stray capacitance, as well as the scope probe used to evaluate these transients, all contribute

to the amplitude of these spikes.

When a switching regulator is operating in the continuous mode, the inductor current waveform ranges from a

triangular to a sawtooth type of waveform (depending on the input voltage). For a given input and output voltage,

the peak-to-peak amplitude of this inductor current waveform remains constant. As the load current increases or

decreases, the entire sawtooth current waveform also rises and falls. The average value (or the center) of this

current waveform is equal to the DC load current.

If the load current drops to a low enough level, the bottom of the sawtooth current waveform will reach zero, and

the switcher will smoothly change from a continuous to a discontinuous mode of operation. Most switcher

designs (irregardless how large the inductor value is) will be forced to run discontinuous if the output is lightly

loaded. This is a perfectly acceptable mode of operation.

Figure 30. Peak-to-Peak Inductor

Ripple Current vs Load Current

In a switching regulator design, knowing the value of the peak-to-peak inductor ripple current (ΔI_IND) can be

useful for determining a number of other circuit parameters. Parameters such as, peak inductor or peak switch

current, minimum load current before the circuit becomes discontinuous, output ripple voltage and output

capacitor ESR can all be calculated from the peak-to-peak ΔI_IND. When the inductor nomographs shown in

Figure 21 through 8 are used to select an inductor value, the peak-to-peak inductor ripple current can

immediately be determined. The curve shown in Figure 30 shows the range of (ΔI_IND) that can be expected for

different load currents. The curve also shows how the peak-to-peak inductor ripple current (ΔI_IND) changes as

you go from the lower border to the upper border (for a given load current) within an inductance region. The

upper border represents a higher input voltage, while the lower border represents a lower input voltage (see

Inductor Selection Guides section).

These curves are only correct for continuous mode operation, and only if the inductor selection guides are used

to select the inductor value

Consider the following example:

V_OUT= 5V, maximum load current of 2.5A

V_IN= 12V, nominal, varying between 10V and 16V.

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The selection guide in Figure 22 shows that the vertical line for a 2.5A load current, and the horizontal line for the

12V input voltage intersect approximately midway between the upper and lower borders of the 33 μH inductance

region. A 33 μH inductor will allow a peak-to-peak inductor current (ΔI_IND) to flow that will be a percentage of the

maximum load current. Referring to Figure 30, follow the 2.5A line approximately midway into the inductance

region, and read the peak-to-peak inductor ripple current (ΔI_IND) on the left hand axis (approximately 620 mA p-

p).

As the input voltage increases to 16V, it approaches the upper border of the inductance region, and the inductor

ripple current increases. Referring to the curve in Figure 30, it can be seen that for a load current of 2.5A, the

peak-to-peak inductor ripple current (ΔI_IND) is 620 mA with 12V in, and can range from 740 mA at the upper

border (16V in) to 500 mA at the lower border (10V in).

Once the ΔI_INDvalue is known, the following formulas can be used to calculate additional information about the

switching regulator circuit.

1. Peak Inductor or peak switch current

2. Minimum load current before the circuit becomes discontinuous

3. Output Ripple Voltage = (ΔI_IND)×(ESR of C_OUT) = 0.62A×0.1Ω = 62 mV p-p

4. added

for

line

break

OPEN CORE INDUCTORS

Another possible source of increased output ripple voltage or unstable operation is from an open core inductor.

Ferrite bobbin or stick inductors have magnetic lines of flux flowing through the air from one end of the bobbin to

the other end. These magnetic lines of flux will induce a voltage into any wire or PC board copper trace that

comes within the inductor's magnetic field. The strength of the magnetic field, the orientation and location of the

PC copper trace to the magnetic field, and the distance between the copper trace and the inductor, determine

the amount of voltage generated in the copper trace. Another way of looking at this inductive coupling is to

consider the PC board copper trace as one turn of a transformer (secondary) with the inductor winding as the

primary. Many millivolts can be generated in a copper trace located near an open core inductor which can cause

stability problems or high output ripple voltage problems.

If unstable operation is seen, and an open core inductor is used, it's possible that the location of the inductor with

respect to other PC traces may be the problem. To determine if this is the problem, temporarily raise the inductor

away from the board by several inches and then check circuit operation. If the circuit now operates correctly,

then the magnetic flux from the open core inductor is causing the problem. Substituting a closed core inductor

such as a torroid or E-core will correct the problem, or re-arranging the PC layout may be necessary. Magnetic

flux cutting the IC device ground trace, feedback trace, or the positive or negative traces of the output capacitor

should be minimized.

Sometimes, locating a trace directly beneath a bobbin in- ductor will provide good results, provided it is exactly in

the center of the inductor (because the induced voltages cancel themselves out), but if it is off center one

direction or the other, then problems could arise. If flux problems are present, even the direction of the inductor

winding can make a difference in some circuits.

This discussion on open core inductors is not to frighten the user, but to alert the user on what kind of problems

to watch out for when using them. Open core bobbin or “stick” inductors are an inexpensive, simple way of

making a compact efficient inductor, and they are used by the millions in many different applications.

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THERMAL CONSIDERATIONS

The LM2596 is available in two packages, a 5-pin TO-220 (T) and a 5-pin surface mount TO-263 (S).

The TO-220 package needs a heat sink under most conditions. The size of the heatsink depends on the input

voltage, the output voltage, the load current and the ambient temperature. The curves in Figure 31 show the

LM2596T junction temperature rises above ambient temperature for a 3A load and different input and output

voltages. The data for these curves was taken with the LM2596T (TO-220 package) operating as a buck

switching regulator in an ambient temperature of 25°C (still air). These temperature rise numbers are all

approximate and there are many factors that can affect these temperatures. Higher ambient temperatures require

more heat sinking.

The TO-263 surface mount package tab is designed to be soldered to the copper on a printed circuit board. The

copper and the board are the heat sink for this package and the other heat producing components, such as the

catch diode and inductor. The PC board copper area that the package is soldered to should be at least 0.4 in²,

and ideally should have 2 or more square inches of 2 oz. (0.0028 in.) copper. Additional copper area improves

the thermal characteristics, but with copper areas greater than approximately 6 in², only small improvements in

heat dissipation are realized. If further thermal improvements are needed, double sided, multilayer PC board with

large copper areas and/or airflow are recommended.

The curves shown in Figure 32 show the LM2596S (TO-263 package) junction temperature rise above ambient

temperature with a 2A load for various input and output voltages. This data was taken with the circuit operating

as a buck switching regulator with all components mounted on a PC board to simulate the junction temperature

under actual operating conditions. This curve can be used for a quick check for the approximate junction

temperature for various conditions, but be aware that there are many factors that can affect the junction

temperature. When load currents higher than 2A are used, double sided or multilayer PC boards with large

copper areas and/or airflow might be needed, especially for high ambient temperatures and high output voltages.

For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper

should be used in the board layout. (One exception to this is the output (switch) pin, which should not have large

areas of copper.) Large areas of copper provide the best transfer of heat (lower thermal resistance) to the

surrounding air, and moving air lowers the thermal resistance even further.

Package thermal resistance and junction temperature rise numbers are all approximate, and there are many

factors that will affect these numbers. Some of these factors include board size, shape, thickness, position,

location, and even board temperature. Other factors are, trace width, total printed circuit copper area, copper

thickness, single- or double-sided, multilayer board and the amount of solder on the board. The effectiveness of

the PC board to dissipate heat also depends on the size, quantity and spacing of other components on the

board, as well as whether the surrounding air is still or moving. Furthermore, some of these components such as

the catch diode will add heat to the PC board and the heat can vary as the input voltage changes. For the

inductor, depending on the physical size, type of core material and the DC resistance, it could either act as a

heat sink taking heat away from the board, or it could add heat to the board.

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Circuit Data for Temperature Rise Curve

TO-220 Package (T)

Through hole electrolytic

Capacitors

Inductor

Diode

Through hole, Renco

Through hole, 5A 40V, Schottky

3 square inches single sided 2 oz. copper (0.0028″)

PC board

Figure 31. Junction Temperature Rise, TO-220

Circuit Data for Temperature Rise Curve

TO-263 Package (S)

Capacitors

Inductor

Diode

Surface mount tantalum, molded “D” size

Surface mount, Pulse Engineering, 68 μH

Surface mount, 5A 40V, Schottky

PC board

9 square inches single sided 2 oz. copper (0.0028″)

Figure 32. Junction Temperature Rise, TO-263

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Figure 33. Delayed Startup

Figure 34. Undervoltage Lockout

for Buck Regulator

DELAYED STARTUP

The circuit in Figure 33 uses the the ON /OFF pin to provide a time delay between the time the input voltage is

applied and the time the output voltage comes up (only the circuitry pertaining to the delayed start up is shown).

As the input voltage rises, the charging of capacitor C1 pulls the ON /OFF pin high, keeping the regulator off.

Once the input voltage reaches its final value and the capacitor stops charging, and resistor R₂pulls the ON

/OFF pin low, thus allowing the circuit to start switching. Resistor R₁is included to limit the maximum voltage

applied to the ON /OFF pin (maximum of 25V), reduces power supply noise sensitivity, and also limits the

capacitor, C1, discharge current. When high input ripple voltage exists, avoid long delay time, because this ripple

can be coupled into the ON /OFF pin and cause problems.

This delayed startup feature is useful in situations where the input power source is limited in the amount of

current it can deliver. It allows the input voltage to rise to a higher voltage before the regulator starts operating.

Buck regulators require less input current at higher input voltages.

UNDERVOLTAGE LOCKOUT

Some applications require the regulator to remain off until the input voltage reaches a predetermined voltage. An

undervoltage lockout feature applied to a buck regulator is shown in Figure 34, while Figure 35 and Figure 36

applies the same feature to an inverting circuit. The circuit in Figure 35 features a constant threshold voltage for

turn on and turn off (zener voltage plus approximately one volt). If hysteresis is needed, the circuit in Figure 36

has a turn ON voltage which is different than the turn OFF voltage. The amount of hysteresis is approximately

equal to the value of the output voltage. If zener voltages greater than 25V are used, an additional 47 kΩ resistor

is needed from the ON /OFF pin to the ground pin to stay within the 25V maximum limit of the ON /OFF pin.

INVERTING REGULATOR

The circuit in Figure 37 converts a positive input voltage to a negative output voltage with a common ground. The

circuit operates by bootstrapping the regulator's ground pin to the negative output voltage, then grounding the

feedback pin, the regulator senses the inverted output voltage and regulates it.

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This circuit has an ON/OFF threshold of approximately 13V.

Figure 35. Undervoltage Lockout

for Inverting Regulator

This example uses the LM2596-5.0 to generate a −5V output, but other output voltages are possible by selecting

other output voltage versions, including the adjustable version. Since this regulator topology can produce an

output voltage that is either greater than or less than the input voltage, the maximum output current greatly

depends on both the input and output voltage. The curve shown in Figure 38 provides a guide as to the amount

of output load current possible for the different input and output voltage conditions.

The maximum voltage appearing across the regulator is the absolute sum of the input and output voltage, and

this must be limited to a maximum of 40V. For example, when converting +20V to −12V, the regulator would see

32V between the input pin and ground pin. The LM2596 has a maximum input voltage spec of 40V.

Additional diodes are required in this regulator configuration. Diode D1 is used to isolate input voltage ripple or

noise from coupling through the C_INcapacitor to the output, under light or no load conditions. Also, this diode

isolation changes the topology to closley resemble a buck configuration thus providing good closed loop stability.

A Schottky diode is recommended for low input voltages, (because of its lower voltage drop) but for higher input

voltages, a fast recovery diode could be used.

Without diode D3, when the input voltage is first applied, the charging current of C_INcan pull the output positive

by several volts for a short period of time. Adding D3 prevents the output from going positive by more than a

diode voltage.

This circuit has hysteresis

Regulator starts switching at V_IN= 13V

Regulator stops switching at V_IN= 8V

Figure 36. Undervoltage Lockout with Hysteresis for Inverting Regulator

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C_IN—68 μF/25V Tant. Sprague 595D

470 μF/50V Elec. Panasonic HFQ

C_OUT—47 μF/20V Tant. Sprague 595D

220 μF/25V Elec. Panasonic HFQ

Figure 37. Inverting −5V Regulator with Delayed Startup

Figure 38. Inverting Regulator Typical Load Current

Because of differences in the operation of the inverting regulator, the standard design procedure is not used to

select the inductor value. In the majority of designs, a 33 μH, 3.5A inductor is the best choice. Capacitor

selection can also be narrowed down to just a few values. Using the values shown in Figure 37 will provide good

results in the majority of inverting designs.

This type of inverting regulator can require relatively large amounts of input current when starting up, even with

light loads. Input currents as high as the LM2596 current limit (approx 4.5A) are needed for at least 2 ms or

more, until the output reaches its nominal output voltage. The actual time depends on the output voltage and the

size of the output capacitor. Input power sources that are current limited or sources that can not deliver these

currents without getting loaded down, may not work correctly. Because of the relatively high startup currents

required by the inverting topology, the delayed startup feature (C1, R₁and R₂) shown in Figure 37 is

recommended. By delaying the regulator startup, the input capacitor is allowed to charge up to a higher voltage

before the switcher begins operating. A portion of the high input current needed for startup is now supplied by the

input capacitor (C_IN). For severe start up conditions, the input capacitor can be made much larger than normal.

INVERTING REGULATOR SHUTDOWN METHODS

To use the ON /OFF pin in a standard buck configuration is simple, pull it below 1.3V (@25°C, referenced to

ground) to turn regulator ON, pull it above 1.3V to shut the regulator OFF. With the inverting configuration, some

level shifting is required, because the ground pin of the regulator is no longer at ground, but is now setting at the

negative output voltage level. Two different shutdown methods for inverting regulators are shown in Figure 39

and Figure 40.

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Figure 39. Inverting Regulator Ground Referenced Shutdown

Figure 40. Inverting Regulator Ground Referenced Shutdown using Opto Device

TYPICAL THROUGH HOLE PC BOARD LAYOUT, FIXED OUTPUT (1X SIZE), DOUBLE SIDED

C_IN—470 μF, 50V, Aluminum Electrolytic Panasonic, “HFQ Series”

C_OUT—330 μF, 35V, Aluminum Electrolytic Panasonic, “HFQ Series”

D1—5A, 40V Schottky Rectifier, 1N5825

L1—47 μH, L39, Renco, Through Hole

Thermalloy Heat Sink #7020

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TYPICAL THROUGH HOLE PC BOARD LAYOUT, ADJUSTABLE OUTPUT (1X SIZE), DOUBLE SIDED

C_IN—470 μF, 50V, Aluminum Electrolytic Panasonic, “HFQ Series”

C_OUT—220 μF, 35V Aluminum Electrolytic Panasonic, “HFQ Series”

D1—5A, 40V Schottky Rectifier, 1N5825

L1—47 μH, L39, Renco, Through Hole

R₁—1 kΩ, 1%

R₂—Use formula in Design Procedure

C_FF—See Table 2.

Thermalloy Heat Sink #7020

Figure 41. PC Board Layout

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REVISION HISTORY

Changes from Revision B (April 2013) to Revision C

Page

•

Changed layout of National Data Sheet to TI format .......................................................................................................... 31

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PACKAGE MATERIALS INFORMATION

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23-Sep-2013

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device

Package Package Pins

Type Drawing

SPQ

Reel

A0

B0

K0

P1

W

Pin1

Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant

(mm) W1 (mm)

LM2596SX-12/NOPB

LM2596SX-3.3

DDPAK/

TO-263

KTT

5

500

330.0

24.4

10.75 14.85

5.0

16.0

24.0

Q2

DDPAK/

TO-263

LM2596SX-3.3/NOPB

LM2596SX-5.0/NOPB

LM2596SX-ADJ

DDPAK/

TO-263

DDPAK/

TO-263

DDPAK/

TO-263

LM2596SX-ADJ/NOPB DDPAK/

TO-263

Pack Materials-Page 1

PACKAGE MATERIALS INFORMATION

www.ti.com

23-Sep-2013

*All dimensions are nominal

Device

Package Type Package Drawing Pins

SPQ

Length (mm) Width (mm) Height (mm)

LM2596SX-12/NOPB

LM2596SX-3.3

DDPAK/TO-263

KTT

5

500

367.0

45.0

LM2596SX-3.3/NOPB

LM2596SX-5.0/NOPB

LM2596SX-ADJ

LM2596SX-ADJ/NOPB

Pack Materials-Page 2

MECHANICAL DATA

NDH0005D

www.ti.com

MECHANICAL DATA

KTT0005B

TS5B (Rev D)

BOTTOM SIDE OF PACKAGE

www.ti.com

MECHANICAL DATA

NEB0005B

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MECHANICAL DATA

NEB0005E

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non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.

Products

Applications

Audio

www.ti.com/audio

amplifier.ti.com

dataconverter.ti.com

www.dlp.com

Automotive and Transportation www.ti.com/automotive

Communications and Telecom www.ti.com/communications

Amplifiers

Data Converters

DLP® Products

DSP

Computers and Peripherals

Consumer Electronics

Energy and Lighting

Industrial

www.ti.com/computers

www.ti.com/consumer-apps

www.ti.com/energy

dsp.ti.com

Clocks and Timers

Interface

www.ti.com/clocks

interface.ti.com

logic.ti.com

www.ti.com/industrial

www.ti.com/medical

Medical

Logic

Security

www.ti.com/security

Power Mgmt

Microcontrollers

RFID

power.ti.com

Space, Avionics and Defense

Video and Imaging

www.ti.com/space-avionics-defense

www.ti.com/video

microcontroller.ti.com

www.ti-rfid.com

www.ti.com/omap

OMAP Applications Processors

Wireless Connectivity

TI E2E Community

e2e.ti.com

www.ti.com/wirelessconnectivity

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265


型号：	PE-53933-S
厂家：	TEXAS INSTRUMENTS
描述：	LM2596 SIMPLE SWITCHERÂ® Power Converter 150 kHz 3A Step-Down Voltage Regulator LM2596 SIMPLE SWITCHERÂ®电源转换器150千赫3A降压型稳压器转换器稳压器
文件：	总42页 (文件大小：4727K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

PE-53933-S [TI]

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