National Semiconductor LM2595 Technical data

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LM2595
SIMPLE SWITCHER
1A Step-Down Voltage Regulator

®

Power Converter 150 kHz

LM2595 SIMPLE SWITCHER Power Converter 150 kHz 1A Step-Down Voltage Regulator

May 1999

General Description

The LM2595 series of regulators are monolithic integrated
circuits that provide all the active functions for a step-down
(buck) switching regulator, capable of driving a 1A 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 aminimumnumber of external components, these
regulators are simple to use and include internal frequency
compensation

The LM2595 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. Typically, for output voltages less
than 12V, and ambient temperatures less than 50˚C, no heat
sink is required.

A standard series of inductors are available from several dif­ferent manufacturers optimized for use with the LM2595 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 85 µAstand-by 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

n Available in TO-220 and TO-263 (surface mount)

n Guaranteed 1A 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

Applications

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

Typical Application (Fixed Output Voltage Versions)

±

4%max over line and load conditions

packages

typically 85 µA

Q

Note:†Patent Number 5,382,918.

DS012565-1

SIMPLE SWITCHER®and

© 1999 National Semiconductor Corporation DS012565 www.national.com

Switchers Made Simple

®

are registered trademarks of National Semiconductor Corporation.

Connection Diagrams and Ordering Information

Bent and Staggered Leads, Through Hole Package

5–Lead TO-220 (T)

DS012565-2

Order Number LM2595T-3.3, LM2595T-5.0,

LM2595T-12 or LM2595T-ADJ

See NS Package Number T05D

Order Number LM2595S-3.3, LM2595S-5.0,

Surface Mount Package

5-Lead TO-263 (S)

DS012565-3

LM2595S-12 or LM2595S-ADJ

See NS Package Number TS5B

16-Lead Ceramic Dual-in-Line Package (J)

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Order Number LM2595J-3.3-QML (5962-9687901QEA),

LM2595J-5.0-QML (5962-9650301QEA),
LM2595J-12-QML (5962-9650201QEA),

or LM2595J-ADJ-QML (5962-9650401QEA)

See NS Package Number J16A

For specifications and information about Military-Aerospace products, please see the Mil-Aero web page at

http://www.national.com/appinfo/milaero/index.html.

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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

−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

ESD Susceptibility

LM2595-3.3
Electrical Characteristics

12V, I

=

25˚C, and those with boldface type apply over full Operating Tempera-

J

Typ Limit

(Note 3) (Note 4)

Figure 1

≤ 1A 3.3 V

LOAD

3.168/3.135 V(min)

3.432/3.465 V(max)

=

1A 78

LOAD

(Limits)

%

Specifications with standard type face are for T

ture Range.

Symbol Parameter Conditions LM2595-3.3 Units

SYSTEM PARAMETERS (Note 5) Test Circuit

V

OUT

η Efficiency V

Output Voltage 4.75V ≤ VIN≤ 40V, 0.1A ≤ I

=

IN

LM2595-5.0
Electrical Characteristics

12V, I

=

25˚C, and those with boldface type apply over full Operating Tempera-

J

Typ Limit

(Note 3) (Note 4)

Figure 1

≤ 1A 5.0 V

LOAD

4.800/4.750 V(min)

5.200/5.250 V(max)

=

1A 82

LOAD

(Limits)

%

Specifications with standard type face are for T

ture Range.

Symbol Parameter Conditions LM2595-5.0 Units

SYSTEM PARAMETERS (Note 5) Test Circuit

V

OUT

η Efficiency V

Output Voltage 7V ≤ VIN≤ 40V, 0.1A ≤ I

=

IN

LM2595-12
Electrical Characteristics

25V, I

=

25˚C, and those with boldface type apply over full Operating Tempera-

J

Typ Limit

(Note 3) (Note 4)

Figure 1

≤ 1A 12.0 V

LOAD

11.52/11.40 V(min)

12.48/12.60 V(max)

=

1A 90

LOAD

(Limits)

%

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Specifications with standard type face are for T

ture Range.

Symbol Parameter Conditions LM2595-12 Units

SYSTEM PARAMETERS (Note 5) Test Circuit

V

OUT

η Efficiency V

Output Voltage 15V ≤ VIN≤ 40V, 0.1A ≤ I

=

IN

LM2595-ADJ
Electrical Characteristics

12V, V

=

25˚C, and those with boldface type apply over full Operating Tempera-

J

Typ Limit

(Note 3) (Note 4)

Figure 1

≤ 1A 1.230 V

LOAD

Figure 1

1.193/1.180 V(min)

1.267/1.280 V(max)

OUT

=

3V, I

=

1A 78

LOAD

(Limits)

%

Specifications with standard type face are for T

ture Range.

Symbol Parameter Conditions LM2595-ADJ Units

SYSTEM PARAMETERS (Note 5) Test Circuit

V

FB

η Efficiency V

Feedback Voltage 4.5V ≤ VIN≤ 40V, 0.1A ≤ I

V

programmed for 3V. Circuit of

OUT

=

IN

All Output Voltage Versions
Electrical Characteristics

Specifications with standard type face are for T
ture Range. Unless otherwise specified, V
sion. I

LOAD

=

200 mA.

Symbol Parameter Conditions LM2595-XX Units

DEVICE PARAMETERS

I

b

f

O

V

SAT

Feedback Bias Current Adjustable Version Only,V

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

I

I

I

CL

L

Q

STBY

Current Limit Peak Current (Notes 7, 8) 1.5 A

Output Leakage Current Output=0V (Notes 7, 9) and (Note 10) 50 µA(max)

Quiescent Current (Note 9) 5 mA

Standby Quiescent ON/OFF pin=5V (OFF) (Note 10) 85 µA
Current 200/250 µA(max)

θ

JC

θ

JA

θ

JA

θ

JA

θ

JA

ON/OFF CONTROL Test Circuit

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)

=

25˚C, and those with boldface type apply over full Operating Tempera-

J

=

12V for the 3.3V, 5V, and Adjustable version and V

IN

=

24V for the 12V ver-

IN

Typ Limit

(Limits)

(Note 3) (Note 4)

=

1.3V 10 nA

FB

50/100 nA (max)

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

=

1A (Notes 7, 8) 1 V

OUT

1.2/1.3 V(max)
%

1.2/1.15 A(min)

2.4/2.6 A(max)

Output=−1V 2 mA

15 mA(max)

10 mA(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)

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All Output Voltage Versions
Electrical Characteristics

Specifications with standard type face are for T
ture Range. Unless otherwise specified, V
sion. I

Symbol Parameter Conditions LM2595-XX Units

ON/OFF CONTROL Test Circuit

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%produc-

tion 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. When the LM2595 is used as shown in the
Characteristics.

Note 6: The switching frequency is reduced when the second stage current limit is activated. The amount of reduction is determined by the severity of current over­load.

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 the ADJ. 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 LM2595S side of the board, and approximately 16 in
model in

=

200 mA.

LOAD

ON/OFF Pin
Input Current

=

40V.

IN

Switchers Made Simple

Figure 1

®

version 4.3 software.

(Continued)

=

25˚C, and those with boldface type apply over full Operating Tempera-

J

=

12V for the 3.3V, 5V, and Adjustable version and V

IN

=

24V for the 12V ver-

IN

Typ Limit

(Note 3) (Note 4)

=

V

V

2

.

2.5V (Regulator OFF) 5 µA

LOGIC

=

0.5V (Regulator ON) 0.02 µA

LOGIC

Figure 1

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

2

of (1 oz.) copper area.

2

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

2

(Limits)

15 µA(max)

5 µA(max)

2

of (1 oz.) copper area.

of (1 oz.) copper area on

Typical Performance Characteristics (Circuit of

Normalized
Output Voltage

DS012565-11

Line Regulation

Figure 1

DS012565-12

)

Efficiency

DS012565-13

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Typical Performance Characteristics (Circuit of

Figure 1

) (Continued)

Switch Saturation
Voltage

Operating
Quiescent Current

ON /OFF Threshold
Voltage

DS012565-14

DS012565-4

Switch Current Limit

Shutdown
Quiescent Current

ON /OFF Pin
Current (Sinking)

DS012565-15

DS012565-5

Dropout Voltage

DS012565-16

Minimum Operating
Supply Voltage

DS012565-6

Switching Frequency

DS012565-7

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DS012565-8

DS012565-9

Typical Performance Characteristics (Circuit of

Feedback Pin
Bias Current

DS012565-10

Figure 1

) (Continued)

Continuous Mode Switching Waveforms

=

V

20V, V

IN

L=68 µH, C

A: Output Pin Voltage, 10V/div.
B: Inductor Current 0.5A/div.
C: Output Ripple Voltage, 50 mV/div.

OUT

OUT

=

5V, I

=

120 µF, C

LOAD

=

1A

ESR=100 mΩ

OUT

Horizontal Time Base: 2 µs/div.

Load Transient Response for Continuous Mode

=

V

20V, V

IN

L=68 µH, C

OUT

OUT

=

5V, I

=

120 µF, C

=

250 mA to 750 mA

LOAD

OUT

ESR=100 mΩ

DS012565-17

Discontinuous Mode Switching Waveforms

=

V

20V, V

IN

L=22 µH, C

A: Output Pin Voltage, 10V/div.
B: Inductor Current 0.5A/div.
C: Output Ripple Voltage, 50 mV/div.

OUT

OUT

=

5V, I

=

220 µF, C

LOAD

=

600 mA

ESR=50 mΩ

OUT

DS012565-18

Horizontal Time Base: 2 µs/div.

Load Transient Response for Discontinuous Mode

=

V

20V, V

IN

L=22 µH, C

OUT

OUT

=

5V, I

=

220 µF, C

=

250 mA to 750 mA

LOAD

OUT

ESR=50 mΩ

A: Output Voltage, 100 mV/div. (AC)
B: 250 mA to 750 mA Load Pulse

Horizontal Time Base: 100 µs/div.

DS012565-19

A: Output Voltage, 100 mV/div. (AC)
B: 250 mA to 750 mA Load Pulse

Horizontal Time Base: 200 µs/div.

DS012565-20

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Test Circuit and Layout Guidelines

Fixed Output Voltage Versions

CIN— 120 µF, 50V,Aluminum Electrolytic Nichicon “PL Series”

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

C

OUT

D1— 3A, 40V Schottky Rectifier, 1N5822
L1— 100 µH, L29

Adjustable Output Voltage Versions

CIN— 120 µF, 50V,Aluminum Electrolytic Nichicon “PL Series”

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

C

OUT

D1— 3A, 40V Schottky Rectifier, 1N5822
L1— 100 µH, L29
R
C

%

—1kΩ,1

1

— See Application Information Section

FF

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, ex-

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

DS012565-22

DS012565-23

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.)

www.national.com 8

LM2595 Series Buck Regulator Design Procedure (Fixed Output)

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

Given:

=

V

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

OUT

(max)=Maximum DC Input Voltage

V

IN

(max)=Maximum Load Current

I

LOAD

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

ure 4

,

Figure 5

,or

Figure 6

. (Output voltages of 3.3V, 5V, or

Fig-

12V respectively.) For all other voltages, see the design pro­cedure for the adjustable version.

B. From the inductor value selectionguide, identify the induc­tance region intersected by the Maximum Input Voltage line
and the Maximum Load Current line. Each region isidentified
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 47 µF and 330
µF and low ESR solid tantalum capacitors between 56 µF
and 270 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 330 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

Made Simple

®

version 4.2 or later.

Switchers

Procedure continued on next page. Example continued on next page.

Given:

=

V

5V

OUT

(max)=12V

V

IN

(max)=1A

I

LOAD

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

in

Figure 5

.

B. From the inductor value selection guide shownin
the inductance region intersected by the 12V horizontal line
and the 1A vertical line is 68 µH, and the inductor code is
L30.

C. The inductance value required is 68 µH. From the table in

Figure 8

, go to the L30 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

OUT

)

A. See section on output capacitors in application infor­mation 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 1A 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.

220 µF 25V Panasonic HFQ Series
220 µF 25V Nichicon PL Series

C. For a 5V output, a capacitor voltage rating at least 7.5V or
more is needed. But, in this example, even a low ESR,
switching grade, 220 µF 10V aluminum electrolytic capacitor
would exhibit approximately 225 mΩ of ESR (see the curve
in

Figure 14

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 voltage rating (lower ESR)should be se­lected. A 16V or 25V capacitor will reduce the ripple voltage
by approximately half.

Figure 5

,

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