National Semiconductor LM2598 Technical data

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LM2598 SIMPLE SWITCHER

Power Converter 150 kHz

1A Step-Down Voltage Regulator, with Features

January 2001

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 additionalsupervisory and performance features added.

Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation 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 put voltage under all conditions of input voltage and output load conditions, and

†

, improved line and load specifications,

4% tolerance on out-

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 n High Efficiency n Uses readily available standard inductors n Thermal shutdown and current limit protection

typically 85 µA

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)

DS012593-1

†

Patent Number 5,382,918.

SIMPLE SWITCHER

and

Switchers Made Simple

are registered trademarks of National Semiconductor Corporation.

Connection Diagrams and Order Information

LM2598

Bent and Staggered Leads, Through Hole Package

7-Lead TO-220 (T)

Surface Mount Package

7-Lead TO-263 (S)

DS012593-50

Order Number LM2598T-3.3, LM2598T-5.0,

LM2598T-12 or LM2598T-ADJ

See NS Package Number TA07B

DS012593-22

Order Number LM2598S-3.3, LM2598S-5.0,

LM2598S-12 or LM2598S-ADJ

See NS Package Number TS7B

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LM2598

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 SD/SS Pin Input Voltage (Note 2) 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

) 45V

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 TJ= 25˚C, and those with boldface type apply over full Operating Temperature Range.

Symbol Parameter Conditions LM2598-3.3 Units

Typ Limit

(Note 4) (Note 5) SYSTEM PARAMETERS (Note 6) Test Circuit V

OUT

η Efficiency V

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

= 12V, I

Figure 1

≤ 1A 3.3 V

LOAD

3.168/3.135 V(min)

3.432/3.465 V(max)

=1A 78 %

LOAD

(Limits)

LM2598-5.0 Electrical Characteristics

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

Symbol Parameter Conditions LM2598-5.0 Units

Typ Limit

(Note 4) (Note 5) SYSTEM PARAMETERS (Note 6) Test Circuit V

OUT

η Efficiency V

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

= 12V, I

Figure 1

≤ 1A 5 V

LOAD

4.800/4.750 V(min)

5.200/5.250 V(max)

=1A 82 %

LOAD

(Limits)

LM2598-12 Electrical Characteristics

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

Symbol Parameter Conditions LM2598-12 Units

Typ Limit

(Note 4) (Note 5) SYSTEM PARAMETERS (Note 6) Test Circuit V

OUT

η Efficiency V

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

= 25V, I

Figure 1

≤ 1A 12 V

LOAD

11.52/11.40 V(min)

12.48/12.60 V(max)

=1A 90 %

LOAD

(Limits)

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LM2598-ADJ Electrical Characteristics

LM2598

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

Symbol Parameter Conditions LM2598-ADJ Units

Typ Limit

(Note 4) (Note 5) SYSTEM PARAMETERS (Note 6) Test Circuit V

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

OUT

Figure 1

≤ 1A 1.230 V

LOAD

programmed for 3V. Circuit of

Figure 12

. 1.193/1.180 V(min)

1.267/1.280 V(max)

η Efficiency V

= 12V, V

OUT

= 3V, I

=1A 78 %

LOAD

All Output Voltage Versions Electrical Characteristics

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

sion. I

LOAD

= 200 mA

Symbol Parameter Conditions LM2598-XX Units

DEVICE PARAMETERS

SAT

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

Oscillator Frequency (Note 7) 150 kHz

Saturation Voltage I

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

Min Duty Cycle (OFF) (Note 10) 0

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

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

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

STBY

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

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

SHUTDOWN/SOFT-START CONTROL Test Circuit of V

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

Soft-start Voltage V

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

Typ Limit

(Note 4) (Note 5)

50/100 nA(max)

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

= 1A (Note 8) (Note 9) 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)

TO220 Package, Junction to Ambient (Note 12) 50 ˚C/W TO263 Package, Junction to Ambient (Note 13) 50 ˚C/W TO263 Package, Junction to Ambient (Note 14) 30 ˚C/W TO263 Package, Junction to Ambient (Note 15) 20 ˚C/W

Figure 1

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

= 20% of Nominal Output Voltage 2 V

OUT

= 100% of Nominal Output Voltage 3

OUT

(Limits)

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All Output Voltage Versions Electrical Characteristics

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

sion. I

Symbol Parameter Conditions LM2598-XX Units

SHUTDOWN/SOFT-START CONTROL Test Circuit of

FLAG/DELAY CONTROL Test Circuit of

SAT

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%

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

Note 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

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 to12Vfor the 3.3V, 5V, and theADJ. version, and 15V for the 12V version, to force theoutput transistor

switch OFF.

Note 11: V Note 12: Junction to ambient thermal resistance (no external heat sink) forthe TO-220 package mounted vertically,with the leads soldered to a printed circuit board

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

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

the LM2598S side of the board, and approximately 16 in

Switchers Made Simple

= 200 mA

LOAD

Shutdown Current V

Soft-start Current V

Regulator Dropout Detector Low (Flag ON) 96 % Threshold Voltage 92 %(min)

Flag Output Saturation I Voltage V Flag Output Leakage

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

Delay Pin Source Current V

Delay Pin Saturation Low (Flag ON) 55 mV

Figure 1

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

= 40V.

version 4.2 software.

(Continued)

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

SHUTDOWN

= 2.5V 1.6 µA

Soft-start

Figure 1

= 3 mA 0.3 V

SINK

= 0.5V 0.7/1.0 V(max)

DELAY

= 40V 0.3 µA

FLAG

High (Flag OFF) and V

= 0.5V 3 µA

DELAY

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

Typ Limit

(Limits)

(Note 4) (Note 5)

Figure 1

= 0.5V 5µA

10 µA(max)

5 µA(max)

98 %(max)

Regulated 1.29 V(max)

OUT

6 µA(max)

350/400 mV(max)

of (1 oz.) copper area.

of (1 oz.) copper area on

LM2598

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Typical Performance Characteristics (Circuit of

LM2598

Normalized Output Voltage

Line Regulation

Figure 1

)

Efficiency

Switch Saturation Voltage

Operating Quiescent Current

DS012593-2

DS012593-15

Switch Current Limit

Shutdown Quiescent Current

DS012593-3

DS012593-16

DS012593-14

Dropout Voltage

DS012593-17

Minimum Operating Supply Voltage

DS012593-4

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DS012593-5

DS012593-6

LM2598

Typical Performance Characteristics (Circuit of

Feedback Pin Bias Current

DS012593-49

Soft-start

Flag Saturation Voltage

Shutdown/Soft-start Current

Figure 1

DS012593-7

) (Continued)

Switching Frequency

DS012593-8

Delay Pin Current

Soft-start Response

DS012593-9

DS012593-10

DS012593-11

Shutdown/Soft-start Threshold Voltage

DS012593-12

DS012593-13

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Typical Performance Characteristics (Circuit of

LM2598

Continuous Mode Switching Waveforms V

= 20V, V

L = 68 µH, C

OUT

=5V,I

LOAD

= 120 µF, C

=1A

ESR = 100 mΩ

OUT

Figure 1

)

Discontinuous Mode Switching Waveforms

= 20V, V

L = 22 µH, C

OUT

=5V,I

LOAD

= 220 µF, C

= 600 mA

ESR=50mΩ

OUT

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.

Load Transient Response for Continuous Mode V

= 20V, V

L = 68 µH, C

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

OUT

=5V,I

LOAD

= 120 µF, C

= 250 mA to 750 mA

ESR = 100 mΩ

OUT

Horizontal Time Base: 100 µs/div.

DS012593-18

DS012593-20

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.

Load Transient Response for Discontinuous Mode

= 20V, V

L = 22 µH, C

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

OUT

=5V,I

LOAD

= 220 µF, C

= 250 mA to 750 mA

ESR=50mΩ

OUT

DS012593-21

Horizontal Time Base: 200 µs/div.

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Test Circuit and Layout Guidelines

Fixed Output Voltage Versions

Component Values shown are for VIN= 15V, V 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

: — 0.1 µF

DELAY

: — 4.7k

Pull Up

OUT

=5V,I

LOAD

= 1A.

Adjustable Output Voltage Versions

LM2598

DS012593-23

where V

REF

= 1.23V

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

= 10V, I

OUT

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

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

OUT

D1 —3A, 40V Schottky Rectifier, 1N5822

LOAD

= 1A.

= 20V,

L1 —100 µH, L29

—1 kΩ,1%

—7.15k, 1%

—3.3 nF, See Application Information Section

—3 kΩ, See Application Information Section

Typical Values

CSS—0.1 µF

—0.1 µF

DELAY

—4.7k

PULL UP

FIGURE 1. Standard Test Circuits and Layout Guides

DS012593-24

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Test Circuit and Layout Guidelines

(Continued)

LM2598

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

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.) switcher lC as possible using ground plane construction or single point grounding.

LM2598 Series Buck Regulator Design Procedure (Fixed Output)

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

Given:

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

OUT

(max) = Maximum DC Input Voltage

(max) = Maximum Load Current I

LOAD

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

Figures

Figure 4,Figure 5

,or

Figure 6

(Output voltages of

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

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

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

2. Output Capacitor Selection (C

Figure 8

) 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.

Given:

=5V

OUT

(max) = 12V

(max) = 1A

LOAD

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

Figure 5

B. From the inductor value selection guide shown in 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.)

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

OUT

Figure 5

)

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