NSC LM2598T-5.0, LM2598T-3.3, LM2598SX-ADJ, LM2598SX-5.0, LM2598SX-3.3 Datasheet

LM2598
SIMPLE SWITCHER

®

Power Converter 150 kHz

1A Step-Down Voltage Regulator, with Features

General Description

The LM2598 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.

This series of switching regulators is similar to the LM2595
series, with additionalsupervisoryand performance features
added.

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

†

, improved line and load specifications,
fixed-frequency oscillator, Shutdown /Soft-start, error flag
delay and error flag output.

The LM2598 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 7-lead TO-220 package with several
different lead bend options, and a 7-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 (both through hole and sur­face mount types) are available from several different manu­facturers optimized for use with the LM2598 series. This fea­ture greatly simplifies the design of switch-mode power
supplies.

Other features include a guaranteed

±

4%tolerance on out­put voltage under all conditions of input voltage and output
load conditions, and

±

15%on the oscillator frequency. Ex-

ternal shutdown is included, featuring typically 85 µA
standby current. Self protection features include a two stage
current limit for the output switch and an over temperature
shutdown for complete protection under fault conditions.

Features

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

±

4%max over line and load conditions

n Guaranteed 1A output current
n Available in 7-pin TO-220 and TO-263 (surface mount)

package

n Input voltage range up to 40V
n Excellent line and load regulation specifications
n 150 kHz fixed frequency internal oscillator
n Shutdown /Soft-start
n Out of regulation error flag
n Error output delay
n Low power standby mode, I

Q

typically 85 µA

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)

†

Patent Number 5,382,918.

SIMPLE SWITCHER

®

and

Switchers Made Simple

®

are registered trademarks of National Semiconductor Corporation.

DS012593-1

March 1998

LM2598 SIMPLE SWITCHER Power Converter 150 kHz 1A Step-Down Voltage Regulator, with

Features

© 1999 National Semiconductor Corporation DS012593 www.national.com

Connection Diagrams and Order Information

Bent and Staggered Leads, Through Hole Package

7-Lead TO-220 (T)

DS012593-50

Order Number LM2598T-3.3, LM2598T-5.0,

LM2598T-12 or LM2598T-ADJ

See NS Package Number TA07B

Surface Mount Package

7-Lead TO-263 (S)

DS012593-22

Order Number LM2598S-3.3, LM2598S-5.0,

LM2598S-12 or LM2598S-ADJ

See NS Package Number TS7B

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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 (V

IN

) 45V

SD/SS Pin Input Voltage (Note 2)

6V
Delay Pin Voltage (Note 2) 1.5V
Flag Pin Voltage −0.3 ≤ V ≤ +45V
Feedback Pin Voltage −0.3 ≤ V ≤ +25V
Output Voltage to Ground

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

ESD Susceptibility

Human Body Model (Note 3) 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 −25˚C ≤ TJ≤ +125˚C
Supply Voltage 4.5V to 40V

LM2598-3.3
Electrical Characteristics

Specifications with standard type face are for T

J

=

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

ture Range.

Symbol Parameter Conditions LM2598-3.3 Units

(Limits)

Typ Limit

(Note 4) (Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit

Figure 1

V

OUT

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

LOAD

≤ 1A 3.3 V

3.168/3.135 V(min)

3.432/3.465 V(max)

η Efficiency V

IN

=

12V, I

LOAD

=

1A 78

%

LM2598-5.0
Electrical Characteristics

Specifications with standard type face are for T

J

=

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

ture Range.

Symbol Parameter Conditions LM2598-5.0 Units

(Limits)

Typ Limit

(Note 4) (Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit

Figure 1

V

OUT

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

LOAD

≤ 1A 5 V

4.800/4.750 V(min)

5.200/5.250 V(max)

η Efficiency V

IN

=

12V, I

LOAD

=

1A 82

%

LM2598-12
Electrical Characteristics

Specifications with standard type face are for T

J

=

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

ture Range.

Symbol Parameter Conditions LM2598-12 Units

(Limits)

Typ Limit

(Note 4) (Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit

Figure 1

V

OUT

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

LOAD

≤ 1A 12 V

11.52/11.40 V(min)

12.48/12.60 V(max)

η Efficiency V

IN

=

25V, I

LOAD

=

1A 90

%

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LM2598-ADJ
Electrical Characteristics

Specifications with standard type face are for T

J

=

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

ture Range.

Symbol Parameter Conditions LM2598-ADJ Units

(Limits)

Typ Limit

(Note 4) (Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit

Figure 1

V

FB

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

LOAD

≤ 1A 1.230 V

V

OUT

programmed for 3V. Circuit of

Figure 12

. 1.193/1.180 V(min)

1.267/1.280 V(max)

η Efficiency V

IN

=

12V, V

OUT

=

3V, I

LOAD

=

1A 78

%

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

=

200 mA

Symbol Parameter Conditions LM2598-XX Units

(Limits)

Typ Limit

(Note 4) (Note 5)

DEVICE PARAMETERS

I

b

Feedback Bias Current Adjustable Version Only, V

FB

=

1.3V 10 nA
50/100 nA(max)

f

O

Oscillator Frequency (Note 7) 150 kHz

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

V

SAT

Saturation Voltage I

OUT

=

1A (Note 8) (Note 9) 1 V

1.2/1.3 V(max)

DC Max Duty Cycle (ON) (Note 9) 100

%

Min Duty Cycle (OFF) (Note 10) 0

I

CL

Current Limit Peak Current, (Note 8) (Note 9) 1.5 A

1.2/1.15 A(min)

2.4/2.6 A(max)

I

L

Output Leakage Current Output=0V (Note 9) (Note 10) (Note 11) 50 µA(max)

Output=−1V 2 mA

15 mA(max)

I

Q

Operating Quiescent SD /SS Pin Open, (Note 10) 5mA
Current 10 mA(max)

I

STBY

Standby Quiescent SD /SS pin=0V, (Note 11) 85 µA
Current 200/250 µA(max)

θ

JC

Thermal Resistance TO220 or TO263 Package, Junction to Case 2 ˚C/W

θ

JA

TO220 Package, Junction to Ambient (Note 12) 50 ˚C/W

θ

JA

TO263 Package, Junction to Ambient (Note 13) 50 ˚C/W

θ

JA

TO263 Package, Junction to Ambient (Note 14) 30 ˚C/W

θ

JA

TO263 Package, Junction to Ambient (Note 15) 20 ˚C/W

SHUTDOWN/SOFT-START CONTROL Test Circuit of

Figure 1

V

SD

Shutdown Threshold 1.3 V
Voltage Low, (Shutdown Mode) 0.6 V(max)

High, (Soft-start Mode) 2 V(min)

V

SS

Soft-start Voltage V

OUT

=

20%of Nominal Output Voltage 2 V

V

OUT

=

100%of Nominal Output Voltage 3

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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

=

200 mA

Symbol Parameter Conditions LM2598-XX Units

(Limits)

Typ Limit

(Note 4) (Note 5)

SHUTDOWN/SOFT-START CONTROL Test Circuit of

Figure 1

I

SD

Shutdown Current V

SHUTDOWN

=

0.5V

5µA

10 µA(max)

I

SS

Soft-start Current V

Soft-start

=

2.5V 1.6 µA
5 µA(max)

FLAG/DELAY CONTROL Test Circuit of

Figure 1

Regulator Dropout Detector Low (Flag ON) 96

%

Threshold Voltage 92

%

(min)

98

%

(max)

VF

SAT

Flag Output Saturation I

SINK

=

3 mA 0.3 V

Voltage V

DELAY

=

0.5V 0.7/1.0 V(max)

IF

L

Flag Output Leakage
Current

V

FLAG

=

40V 0.3 µA

Delay Pin Threshold 1.25 V
Voltage Low (Flag ON) 1.21 V(min)

High (Flag OFF) and V

OUT

Regulated 1.29 V(max)

Delay Pin Source Current V

DELAY

=

0.5V 3 µA
6 µA(max)

Delay Pin Saturation Low (Flag ON) 55 mV

350/400 mV(max)

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: Voltage internally clamped. If clamp voltage is exceeded, limit current to a maximum of 1 mA.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin.
Note 4: Typical numbers are at 25˚C and represent the most likely norm.
Note 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%pro-

duction 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 6: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM2598
is used as shown in the

Figure 1

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

Note 7: 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 8: No diode, inductor or capacitor connected to output pin.
Note 9: Feedback pin removed from output and connected to 0V to force the output transistor switch ON.
Note 10: Feedback pin removed from output and connected to 12V for the 3.3V, 5V,andtheADJ. version, and 15V for the 12V version, to force the output transistor

switch OFF.
Note 11: V

IN

=

40V.

Note 12: 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

2

.

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

2

of (1 oz.) copper area.

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

2

of (1 oz.) copper area.

Note 15: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in

2

of (1 oz.) copper area on

the LM2598S side of the board, and approximately 16 in

2

of copper on the other side of the p-c board. See application hints in this data sheet and the thermal model

in

Switchers Made Simple

®

version 4.2 software.

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Typical Performance Characteristics (Circuit of

Figure 1

)

Normalized
Output Voltage

DS012593-2

Line Regulation

DS012593-3

Efficiency

DS012593-14

Switch Saturation
Voltage

DS012593-15

Switch Current Limit

DS012593-16

Dropout Voltage

DS012593-17

Operating
Quiescent Current

DS012593-4

Shutdown
Quiescent Current

DS012593-5

Minimum Operating
Supply Voltage

DS012593-6

Feedback Pin
Bias Current

DS012593-49

Flag Saturation
Voltage

DS012593-7

Switching Frequency

DS012593-8

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Typical Performance Characteristics (Circuit of

Figure 1

) (Continued)

Typical Performance Characteristics (Circuit of

Figure 1

)

Soft-start

DS012593-9

Shutdown/Soft-start
Current

DS012593-10

Delay Pin Current

DS012593-11

Soft-start Response

DS012593-12

Shutdown/Soft-start
Threshold Voltage

DS012593-13

Continuous Mode Switching Waveforms
V

IN

=

20V, V

OUT

=

5V, I

LOAD

=

1A

L=68 µH, C

OUT

=

120 µF, C

OUT

ESR=100 mΩ

DS012593-18

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

Horizontal Time Base: 2 µs/div.

Discontinuous Mode Switching Waveforms
V

IN

=

20V, V

OUT

=

5V, I

LOAD

=

600 mA

L=22 µH, C

OUT

=

220 µF, C

OUT

ESR=50 mΩ

DS012593-19

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

Horizontal Time Base: 2 µs/div.

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Typical Performance Characteristics (Circuit of

Figure 1

) (Continued)

Load Transient Response for Continuous Mode
V

IN

=

20V, V

OUT

=

5V, I

LOAD

=

250 mA to 750 mA

L=68 µH, C

OUT

=

120 µF, C

OUT

ESR=100 mΩ

DS012593-20

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

Horizontal Time Base: 100 µs/div.

Load Transient Response for Discontinuous Mode
V

IN

=

20V, V

OUT

=

5V, I

LOAD

=

250 mA to 750 mA

L=22 µH, C

OUT

=

220 µF, C

OUT

ESR=50 mΩ

DS012593-21

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

Horizontal Time Base: 200 µs/div.

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Test Circuit and Layout Guidelines

Fixed Output Voltage Versions

DS012593-23

Component Values shown are for V

IN

=

15V, V

OUT

=

5V, I

LOAD

=

1A.
120 µF, 50V, Aluminum Electrolytic Nichicon “PL Series”
120 µF, 35V Aluminum Electrolytic, Nichicon “PL Series”
3A, 40V Schottky Rectifier, 1N5822
68 µH, L30

Typical Values

*CSS: — 0.1 µF
C

DELAY

: — 0.1 µF

R

Pull Up

: — 4.7k

Adjustable Output Voltage Versions

DS012593-24

where V

REF

=

1.23V

Select R1to be approximately 1kΩ,usea1%resistor for best stability.
Component Values shown are for V

IN

=

20V,

V

OUT

=

10V, I

LOAD

=

1A.

C

IN

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

C

OUT

— 120 µF, 35V Aluminum Electrolytic, Nichicon “PL Series”
D1 — 3A, 40V Schottky Rectifier, 1N5822
L1 — 100 µH, L29
R

1

—1kΩ,1

%

R

2

— 7.15k, 1

%

C

FF

— 3.3 nF, See Application Information Section

R

FF

—3kΩ, See Application Information Section

Typical Values

CSS— 0.1 µF
C

DELAY

— 0.1 µF

R

PULL UP

— 4.7k

FIGURE 1. Standard Test Circuits and Layout Guides

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Test Circuit and Layout Guidelines

(Continued)

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.

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

OUT

wiring 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 section for more
information.)

LM2598 Series Buck Regulator Design Procedure (Fixed Output)

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

Given:

Given:

V

OUT

=

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

V

OUT

=

5V

V

IN

(max)=Maximum DC Input Voltage

V

IN

(max)=12V

I

LOAD

(max)=Maximum Load Current I

LOAD

(max)=1A

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

ures

Figure 4,Figure 5

,or

Figure 6

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

A. Use the inductor selection guide for the 5V version shown
in

Figure 5

.

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

B. From the inductor value selection guide shown in

Figure 5

,
the inductance region intersected by the 12V horizontal line
and the 1A vertical line is 68 µH, and the inductor code is
L30.

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

Figure 8

.

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

) 2. Output Capacitor Selection (C

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.

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

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