LM2575HV3.3MWC_技术文档

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January 2004

LM1575/LM2575/LM2575HV

SIMPLE SWITCHER^®1A Step-Down Voltage Regulator

General Description

Features

n 3.3V, 5V, 12V, 15V, and adjustable output versions

n Adjustable version output voltage range,

1.23V to 37V (57V for HV version) 4% max over

line and load conditions

The LM2575 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 avail-

able in fixed output voltages of 3.3V, 5V, 12V, 15V, and an

adjustable output version.

n Guaranteed 1A output current

n Wide input voltage range, 40V up to 60V for HV version

n Requires only 4 external components

n 52 kHz fixed frequency internal oscillator

n TTL shutdown capability, low power standby mode

n High efficiency

n Uses readily available standard inductors

n Thermal shutdown and current limit protection

n P⁺Product Enhancement tested

Requiring a minimum number of external components, these

regulators are simple to use and include internal frequency

compensation and a fixed-frequency oscillator.

The LM2575 series offers a high-efficiency replacement for

popular three-terminal linear regulators. It substantially re-

duces the size of the heat sink, and in many cases no heat

sink is required.

A standard series of inductors optimized for use with the

LM2575 are available from several different manufacturers.

This feature greatly simplifies the design of switch-mode

power supplies.

Applications

n Simple high-efficiency step-down (buck) regulator

n Efficient pre-regulator for linear regulators

n On-card switching regulators

Other features include a guaranteed 4% tolerance on out-

put voltage within specified input voltages and output load

conditions, and 10% on the oscillator frequency. External

shutdown is included, featuring 50 µA (typical) standby cur-

rent. The output switch includes cycle-by-cycle current limit-

ing, as well as thermal shutdown for full protection under

fault conditions.

n Positive to negative converter (Buck-Boost)

Typical Application (Fixed Output Voltage

Versions)

01147501

Note: Pin numbers are for the TO-220 package.

SIMPLE SWITCHER^®is a registered trademark of National Semiconductor Corporation.

DS011475

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Block Diagram and Typical Application

01147502

3.3V, R2 = 1.7k

5V, R2 = 3.1k

12V, R2 = 8.84k

15V, R2 = 11.3k

For ADJ. Version

R1 = Open, R2 = 0Ω

Note: Pin numbers are for the TO-220 package.

FIGURE 1.

Connection Diagrams ^{(XX indicates output voltage option. See Ordering Information table for complete part}

number.)

Straight Leads

5–Lead TO-22 (T)

Bent, Staggered Leads

5-Lead TO-220 (T)

01147524

01147522

01147523

Side View

Top View

LM2575T-XX Flow LB03 or

LM2575HVT-XX Flow LB03

See NS Package Number T05D

LM2575T-XX or LM2575HVT-XX

See NS Package Number T05A

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2

Connection Diagrams (XX indicates output voltage option. See Ordering Information table for complete part

number.) (Continued)

16–Lead DIP (N or J)

24-Lead Surface Mount (M)

01147525

*No Internal Connection

Top View

01147526

LM2575N-XX or LM2575HVN-XX

See NS Package Number N16A

LM1575J-XX-QML

*No Internal Connection

Top View

LM2575M-XX or LM2575HVM-XX

See NS Package Number M24B

See NS Package Number J16A

TO-263(S)

5-Lead Surface-Mount Package

01147529

Top View

01147530

Side View

LM2575S-XX or LM2575HVS-XX

See NS Package Number TS5B

Ordering Information

Package

NSC

Standard

High

Temperature

Range

Type

Package

Number

Voltage Rating

(40V)

Voltage Rating

(60V)

5-Lead TO-220

Straight Leads

T05A

LM2575T-3.3

LM2575HVT-3.3

LM2575T-5.0

LM2575HVT-5.0

LM2575T-12

LM2575HVT-12

LM2575T-15

LM2575HVT-15

LM2575T-ADJ

LM2575HVT-ADJ

5-Lead TO-220

Bent and

T05D

LM2575T-3.3 Flow LB03

LM2575T-5.0 Flow LB03

LM2575T-12 Flow LB03

LM2575T-15 Flow LB03

LM2575T-ADJ Flow LB03

LM2575HVT-3.3 Flow LB03

LM2575HVT-5.0 Flow LB03

LM2575HVT-12 Flow LB03

LM2575HVT-15 Flow LB03

LM2575HVT-ADJ Flow LB03

Staggered Leads

3

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Ordering Information (Continued)

Package

NSC

Standard

Voltage Rating

(40V)

High

Voltage Rating

(60V)

Temperature

Range

Type

Package

Number

16-Pin Molded

DIP

N16A

LM2575N-5.0

LM2575HVN-5.0

−40˚C ≤ T_J≤ +125˚C

LM2575N-12

LM2575HVN-12

LM2575HVN-15

LM2575HVN-ADJ

LM2575HVM-5.0

LM2575HVM-12

LM2575HVM-15

LM2575HVM-ADJ

LM2575HVS-3.3

LM2575HVS-5.0

LM2575HVS-12

LM2575HVS-15

LM2575HVS-ADJ

LM2575N-15

LM2575N-ADJ

LM2575M-5.0

LM2575M-12

24-Pin

M24B

TS5B

Surface Mount

LM2575M-15

LM2575M-ADJ

LM2575S-3.3

5-Lead TO-263

Surface Mount

LM2575S-5.0

LM2575S-12

LM2575S-15

LM2575S-ADJ

LM1575J-3.3-QML

LM1575J-5.0-QML

LM1575J-12-QML

LM1575J-15-QML

LM1575J-ADJ-QML

16-Pin Ceramic

DIP

J16A

−55˚C ≤ T_J≤ +150˚C

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4

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Minimum ESD Rating

(C = 100 pF, R = 1.5 kΩ)

Lead Temperature

2 kV

(Soldering, 10 sec.)

260˚C

Maximum Supply Voltage

LM1575/LM2575

45V

63V

Operating Ratings

LM2575HV

Temperature Range

ON /OFF Pin Input Voltage

Output Voltage to Ground

(Steady State)

−0.3V ≤ V ≤ +V_IN

LM1575

−55˚C ≤ T_J≤ +150˚C

−40˚C ≤ T_J≤ +125˚C

LM2575/LM2575HV

Supply Voltage

LM1575/LM2575

LM2575HV

−1V

Internally Limited

−65˚C to +150˚C

150˚C

Power Dissipation

40V

60V

Storage Temperature Range

Maximum Junction Temperature

LM1575-3.3, LM2575-3.3, LM2575HV-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

Typ

LM1575-3.3

LM2575-3.3

LM2575HV-3.3

Limit

Units

(Limits)

Limit

(Note 2)

(Note 3)

SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2

V_OUT

η

Output Voltage

V_IN= 12V, I_LOAD= 0.2A

3.3

75

V

Circuit of Figure 2

3.267

3.333

3.234

3.366

V(Min)

V(Max)

V

Output Voltage

4.75V ≤ V_IN≤ 40V, 0.2A ≤ I_LOAD≤ 1A

Circuit of Figure 2

LM1575/LM2575

3.200/3.168

3.400/3.432

3.168/3.135

3.432/3.465

V(Min)

V(Max)

V

Output Voltage

LM2575HV

4.75V ≤ V_IN≤ 60V, 0.2A ≤ I_LOAD≤ 1A

Circuit of Figure 2

3.200/3.168

3.416/3.450

3.168/3.135

3.450/3.482

V(Min)

V(Max)

%

Efficiency

V_IN= 12V, I_LOAD= 1A

LM1575-5.0, LM2575-5.0, LM2575HV-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

Typ

LM1575-5.0

LM2575-5.0

LM2575HV-5.0

Limit

Units

(Limits)

Limit

(Note 2)

(Note 3)

SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2

V_OUT

Output Voltage

V_IN= 12V, I_LOAD= 0.2A

5.0

V

Circuit of Figure 2

4.950

5.050

4.900

5.100

V(Min)

V(Max)

V

Output Voltage

0.2A ≤ I_LOAD≤ 1A,

8V ≤ V_IN≤ 40V

LM1575/LM2575

4.850/4.800

5.150/5.200

4.800/4.750

5.200/5.250

V(Min)

V(Max)

V

Circuit of Figure 2

0.2A ≤ I_LOAD≤ 1A,

8V ≤ V_IN≤ 60V

Output Voltage

LM2575HV

4.850/4.800

5.175/5.225

4.800/4.750

5.225/5.275

V(Min)

V(Max)

Circuit of Figure 2

5

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LM1575-5.0, LM2575-5.0, LM2575HV-5.0

Electrical Characteristics ^(Continued)

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

Typ

LM1575-5.0

LM2575-5.0

LM2575HV-5.0

Limit

Units

(Limits)

Limit

(Note 2)

(Note 3)

η

Efficiency

V_IN= 12V, I_LOAD= 1A

77

%

LM1575-12, LM2575-12, LM2575HV-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

Typ

LM1575-12

LM2575-12

LM2575HV-12

Limit

Units

(Limits)

Limit

(Note 2)

(Note 3)

SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2

V_OUT

η

Output Voltage

V_IN= 25V, I_LOAD= 0.2A

12

88

V

Circuit of Figure 2

11.88

12.12

11.76

12.24

V(Min)

V(Max)

V

Output Voltage

0.2A ≤ I_LOAD≤ 1A,

15V ≤ V_IN≤ 40V

LM1575/LM2575

11.64/11.52

12.36/12.48

11.52/11.40

12.48/12.60

V(Min)

V(Max)

V

Circuit of Figure 2

0.2A ≤ I_LOAD≤ 1A,

15V ≤ V_IN≤ 60V

Output Voltage

LM2575HV

11.64/11.52

12.42/12.54

11.52/11.40

12.54/12.66

V(Min)

V(Max)

%

Circuit of Figure 2

V_IN= 15V, I_LOAD= 1A

Efficiency

LM1575-15, LM2575-15, LM2575HV-15

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

Typ

LM1575-15

LM2575-15

LM2575HV-15

Limit

Units

(Limits)

Limit

(Note 2)

(Note 3)

SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2

V_OUT

η

Output Voltage

V_IN= 30V, I_LOAD= 0.2A

15

88

V

Circuit of Figure 2

14.85

15.15

14.70

15.30

V(Min)

V(Max)

V

Output Voltage

0.2A ≤ I_LOAD≤ 1A,

18V ≤ V_IN≤ 40V

LM1575/LM2575

14.55/14.40

15.45/15.60

14.40/14.25

15.60/15.75

V(Min)

V(Max)

V

Circuit of Figure 2

0.2A ≤ I_LOAD≤ 1A,

18V ≤ V_IN≤ 60V

Output Voltage

LM2575HV

14.55/14.40

14.40/14.25

15.68/15.83

V(Min)

V(Max)

%

Circuit of Figure 2

V_IN= 18V, I_LOAD= 1A

15.525/15.675

Efficiency

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6

LM1575-ADJ, LM2575-ADJ, LM2575HV-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.

Symbol

Parameter

Conditions

Typ

LM1575-ADJ

LM2575-ADJ

LM2575HV-ADJ

Limit

Units

(Limits)

Limit

(Note 2)

(Note 3)

SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2

V_OUT

η

Feedback Voltage

V_IN= 12V, I_LOAD= 0.2A

V_OUT= 5V

1.230

77

V

1.217

1.243

1.217

1.243

V(Min)

V(Max)

V

Circuit of Figure 2

Feedback Voltage

LM1575/LM2575

0.2A ≤ I_LOAD≤ 1A,

8V ≤ V_IN≤ 40V

1.205/1.193

1.255/1.267

1.193/1.180

1.267/1.280

V(Min)

V(Max)

V

V_OUT= 5V, Circuit of Figure 2

0.2A ≤ I_LOAD≤ 1A,

Feedback Voltage

LM2575HV

8V ≤ V_IN≤ 60V

1.205/1.193

1.261/1.273

1.193/1.180

1.273/1.286

V(Min)

V(Max)

%

V_OUT= 5V, Circuit of Figure 2

V_IN= 12V, I_LOAD= 1A, V_OUT= 5V

Efficiency

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 Tempera-

ture Range. Unless otherwise specified, V_IN= 12V for the 3.3V, 5V, and Adjustable version, V_IN= 25V for the 12V version,

and V_IN= 30V for the 15V version. I_LOAD= 200 mA.

Symbol

Parameter

Conditions

Typ LM1575-XX

LM2575-XX

LM2575HV-XX

Limit

Units

(Limits)

Limit

(Note 2)

(Note 3)

DEVICE PARAMETERS

I_b

Feedback Bias Current V_OUT= 5V (Adjustable Version Only)

50

52

100/500

nA

kHz

f_O

Oscillator Frequency

(Note 13)

47/43

58/62

47/42

58/63

kHz(Min)

kHz(Max)

V

V_SAT

DC

Saturation Voltage

Max Duty Cycle (ON)

Current Limit

I_OUT= 1A (Note 5)

(Note 6)

0.9

98

1.2/1.4

V(Max)

%

93

%(Min)

A

I_CL

Peak Current (Notes 5, 13)

2.2

1.7/1.3

3.0/3.2

2

1.7/1.3

3.0/3.2

2

A(Min)

A(Max)

mA(Max)

mA

I_L

Output Leakage

Current

(Notes 7, 8)

(Note 7)

Output = 0V

Output = −1V

7.5

5

30

10

mA(Max)

mA

I_Q

Quiescent Current

10/12

mA(Max)

µA

I_STBY

Standby Quiescent

Current

ON /OFF Pin = 5V (OFF)

50

200/500

200

µA(Max)

7

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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 Tempera-

ture Range. Unless otherwise specified, V_IN= 12V for the 3.3V, 5V, and Adjustable version, V_IN= 25V for the 12V version,

and V_IN= 30V for the 15V version. I_LOAD= 200 mA.

Symbol

Parameter

Conditions

Typ LM1575-XX

LM2575-XX

LM2575HV-XX

Limit

Units

(Limits)

Limit

(Note 2)

(Note 3)

DEVICE PARAMETERS

θ_JA

θ_JC

θ_JA

Thermal Resistance

T Package, Junction to Ambient (Note 9)

T Package, Junction to Ambient (Note 10)

T Package, Junction to Case

65

45

2

˚C/W

N Package, Junction to Ambient (Note 11)

M Package, Junction to Ambient (Note 11)

S Package, Junction to Ambient (Note 12)

85

100

37

ON /OFF CONTROL Test Circuit Figure 2

V_IH

V_IL

I_IH

ON /OFF Pin Logic

Input Level

V_OUT= 0V

1.4

1.2

12

2.2/2.4

1.0/0.8

2.2/2.4

1.0/0.8

V(Min)

V(Max)

µA

V_OUT= Nominal Output Voltage

ON /OFF Pin = 5V (OFF)

ON /OFF Pin Input

Current

30

µA(Max)

µA

I_IL

ON /OFF Pin = 0V (ON)

0

10

µA(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: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All limits are used to calculate Average

Outgoing Quality Level, and all are 100% production tested.

Note 3: 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.

Note 4: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the

LM1575/LM2575 is used as shown in the Figure 2 test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.

Note 5: Output (pin 2) sourcing current. No diode, inductor or capacitor connected to output pin.

Note 6: Feedback (pin 4) removed from output and connected to 0V.

Note 7: Feedback (pin 4) removed from output and connected to +12V for the Adjustable, 3.3V, and 5V versions, and +25V for the 12V and 15V versions, to force

the output transistor OFF.

Note 8: V = 40V (60V for the high voltage version).

IN

Note 9: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with ¹

board with minimum copper area.

Note 10: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with ¹

⁄

2

inch leads in a socket, or on a PC

inch leads soldered to a PC board

⁄

2

containing approximately 4 square inches of copper area surrounding the leads.

Note 11: Junction to ambient thermal resistance with approximately 1 square inch of pc board copper surrounding the leads. Additional copper area will lower

thermal resistance further. See thermal model in Switchers made Simple software.

Note 12: If the TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package: Using

0.5 square inches of copper area, θ is 50˚C/W; with 1 square inch of copper area, θ is 37˚C/W; and with 1.6 or more square inches of copper area, θ is 32˚C/W.

JA

Note 13: The oscillator frequency reduces to approximately 18 kHz in the event of an output short or an overload which causes the regulated output voltage to drop

approximately 40% from the nominal output voltage. This self protection feature lowers the average power dissipation of the IC by lowering the minimum duty cycle

from 5% down to approximately 2%.

Note 14: Refer to RETS LM1575J for current revision of military RETS/SMD.

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8

Typical Performance Characteristics (Circuit of Figure 2)

Normalized Output Voltage

Line Regulation

Dropout Voltage

01147534

01147537

01147540

01147543

01147532

01147533

01147536

01147539

Standby

Quiescent Current

Current Limit

Quiescent Current

01147535

Switch Saturation

Voltage

Oscillator Frequency

Efficiency

01147538

Quiescent Current

vs Duty Cycle

Feedback Voltage

vs Duty Cycle

Minimum Operating Voltage

01147541

01147542

9

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Typical Performance Characteristics (Circuit of Figure 2) (Continued)

Maximum Power Dissipation

Feedback Pin Current

(TO-263) (See (Note 12))

01147528

01147505

Switching Waveforms

Load Transient Response

01147506

01147507

V

OUT

= 5V

A: Output Pin Voltage, 10V/div

B: Output Pin Current, 1A/div

C: Inductor Current, 0.5A/div

D: Output Ripple Voltage, 20 mV/div,

AC-Coupled

Horizontal Time Base: 5 µs/div

Single-point grounding (as indicated) or ground plane con-

struction should be used for best results. When using the

Adjustable version, physically locate the programming resis-

tors near the regulator, to keep the sensitive feedback wiring

short.

Test Circuit and Layout Guidelines

As in any switching regulator, layout is very important. Rap-

idly switching currents associated with wiring inductance

generate voltage transients which can cause problems. For

minimal inductance and ground loops, the length of the leads

indicated by heavy lines should be kept as short as possible.

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Test Circuit and Layout Guidelines (Continued)

Fixed Output Voltage Versions

01147508

C

— 100 µF, 75V, Aluminum Electrolytic

IN

— 330 µF, 25V, Aluminum Electrolytic

OUT

D1 — Schottky, 11DQ06

L1 — 330 µH, PE-52627 (for 5V in, 3.3V out, use 100 µH, PE-92108)

Adjustable Output Voltage Version

01147509

where V

= 1.23V, R1 between 1k and 5k.

REF

R1 — 2k, 0.1%

R2 — 6.12k, 0.1%

Note: Pin numbers are for the TO-220 package.

FIGURE 2.

11

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LM2575 Series Buck Regulator Design Procedure

PROCEDURE (Fixed Output Voltage Versions)

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

15V) V_IN(Max) = Maximum Input Voltage I_LOAD(Max) =

Maximum Load Current

EXAMPLE (Fixed Output Voltage Versions)

Given: V_OUT= 5V V_IN(Max) = 20V I_LOAD(Max) = 0.8A

1. Inductor Selection (L1) A. Select the correct Inductor

value selection guide from Figures 3, 4, 5, 6 (Output

voltages of 3.3V, 5V, 12V or 15V respectively). For other

output voltages, see the design procedure for the adjustable

version. B. From the inductor value selection guide, identify

the inductance region intersected by V_IN(Max) and

I_LOAD(Max), and note the inductor code for that region. C.

Identify the inductor value from the inductor code, and

select an appropriate inductor from the table shown in

Figure 9. Part numbers are listed for three inductor

manufacturers. The inductor chosen must be rated for

operation at the LM2575 switching frequency (52 kHz) and

for a current rating of 1.15 x I_LOAD. For additional inductor

information, see the inductor section in the Application Hints

section of this data sheet.

1. Inductor Selection (L1) A. Use the selection guide

shown in Figure 4. B. From the selection guide, the

inductance area intersected by the 20V line and 0.8A line is

L330. C. Inductor value required is 330 µH. From the table

in Figure 9, choose AIE 415-0926, Pulse Engineering

PE-52627, or RL1952.

2. Output Capacitor Selection (C_OUT) A. The value of the

output capacitor together with the inductor defines the

dominate pole-pair of the switching regulator loop. For

stable operation and an acceptable output ripple voltage,

(approximately 1% of the output voltage) a value between

100 µF and 470 µF is recommended. B. The capacitor’s

voltage rating should be at least 1.5 times greater than the

output voltage. For a 5V regulator, a rating of at least 8V is

appropriate, and a 10V or 15V rating is recommended.

Higher voltage electrolytic capacitors generally have lower

ESR numbers, and for this reason it may be necessary to

select a capacitor rated for a higher voltage than would

normally be needed.

2. Output Capacitor Selection (C_OUT) A. C_OUT= 100 µF

to 470 µF standard aluminum electrolytic. B. Capacitor

voltage rating = 20V.

3. Catch Diode Selection (D1) A. The catch-diode current

rating must be at least 1.2 times greater than the maximum

load current. Also, if the power supply design must

withstand a continuous output short, the diode should have

a current rating equal to the maximum current limit of the

LM2575. 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.

3. Catch Diode Selection (D1) A. For this example, a 1A

current rating is adequate. B. Use a 30V 1N5818 or SR103

Schottky diode, or any of the suggested fast-recovery

diodes shown in Figure 8.

4. Input Capacitor (C_IN) An aluminum or tantalum

electrolytic bypass capacitor located close to the regulator is

needed for stable operation.

4. Input Capacitor (C_IN) A 47 µF, 25V aluminum electrolytic

capacitor located near the input and ground pins provides

sufficient bypassing.

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Inductor Value Selection Guides (For Continuous Mode Operation)

01147512

01147510

FIGURE 5. LM2575(HV)-12

FIGURE 3. LM2575(HV)-3.3

01147513

01147511

FIGURE 6. LM2575(HV)-15

FIGURE 4. LM2575(HV)-5.0

01147514

FIGURE 7. LM2575(HV)-ADJ

13

www.national.com

Inductor Value Selection Guides (For Continuous Mode Operation) (Continued)

PROCEDURE (Adjustable Output Voltage Versions)

Given: V_OUT= Regulated Output Voltage V_IN(Max) =

Maximum Input Voltage I_LOAD(Max) = Maximum Load

Current F = Switching Frequency (Fixed at 52 kHz)

1. Programming Output Voltage (Selecting R1 and R2, as

shown in Figure 2 ) Use the following formula to select the

appropriate resistor values.

EXAMPLE (Adjustable Output Voltage Versions)

Given: V_OUT= 10V V_IN(Max) = 25V I_LOAD(Max) = 1A F =

52 kHz

1.Programming Output Voltage (Selecting R1 and R2)

R₁can be between 1k and 5k. (For best temperature coef-

ficient and stability with time, use 1% metal film resistors)

R2 = 1k (8.13 − 1) = 7.13k, closest 1% value is 7.15k

2. Inductor Selection (L1) A. Calculate the inductor Volt •

microsecond constant, E • T (V • µs), from the following

formula:

2. Inductor Selection (L1) A. Calculate E • T (V • µs)

B. E • T = 115 V • µs C. I_LOAD(Max) = 1A D. Inductance

Region = H470 E. Inductor Value = 470 µH Choose from AIE

part #430-0634, Pulse Engineering part #PE-53118, or

Renco part #RL-1961.

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 7. C. On the hori-

zontal axis, select the maximum load current. D. Identify the

inductance region intersected by the E • T value and the

maximum load current value, and note the inductor code for

that region. E. Identify the inductor value from the inductor

code, and select an appropriate inductor from the table shown

in Figure 9. Part numbers are listed for three inductor manu-

facturers. The inductor chosen must be rated for operation at

the LM2575 switching frequency (52 kHz) and for a current

rating of 1.15 x I_LOAD. For additional inductor information, see

the inductor section in the application hints section of this data

sheet.

3. Output Capacitor Selection (C_OUT) A. The value of the

output capacitor together with the inductor defines the

dominate pole-pair of the switching regulator loop. For

stable operation, the capacitor must satisfy the following

requirement:

3. Output Capacitor Selection (C_OUT) A.

However, for acceptable output ripple voltage select C_OUT

220 µF C_OUT= 220 µF electrolytic capacitor

≥

The above formula yields capacitor values between 10 µF

and 2000 µF that will satisfy the loop requirements for stable

operation. But to achieve an acceptable output ripple voltage,

(approximately 1% of the output voltage) and transient re-

sponse, the output capacitor may need to be several times

larger than the above formula yields. B. The capacitor’s volt-

age rating should be at last 1.5 times greater than the output

voltage. For a 10V regulator, a rating of at least 15V or more

is recommended. Higher voltage electrolytic capacitors gen-

erally have lower ESR numbers, and for this reason it may be

necessary to select a capacitor rate for a higher voltage than

would normally be needed.

4. Catch Diode Selection (D1) A. The catch-diode current

rating must be at least 1.2 times greater than the maximum

load current. Also, if the power supply design must

4. Catch Diode Selection (D1) A. For this example, a 3A

current rating is adequate. B. Use a 40V MBR340 or

31DQ04 Schottky diode, or any of the suggested

fast-recovery diodes in Figure 8.

withstand a continuous output short, the diode should have

a current rating equal to the maximum current limit of the

LM2575. The most stressful condition for this diode is an

overload or shorted output. See diode selection guide in

Figure 8. B. The reverse voltage rating of the diode should

be at least 1.25 times the maximum input voltage.

www.national.com

14

Inductor Value Selection Guides (For Continuous Mode Operation) (Continued)

PROCEDURE (Adjustable Output Voltage Versions)

5. Input Capacitor (C_IN) An aluminum or tantalum

electrolytic bypass capacitor located close to the regulator is

needed for stable operation.

EXAMPLE (Adjustable Output Voltage Versions)

5. Input Capacitor (C_IN) A 100 µF aluminum electrolytic

capacitor located near the input and ground pins provides

sufficient bypassing.

To further simplify the buck regulator design procedure, National Semiconductor is making available computer design software to

be used with the Simple Switcher line of switching regulators. Switchers Made Simple (version 3.3) is available on a (3¹⁄

")

2

diskette for IBM compatible computers from a National Semiconductor sales office in your area.

15

www.national.com

Inductor Value Selection Guides (For Continuous Mode Operation) (Continued)

V_R

Schottky

Fast Recovery

1A 3A

1A

3A

1N5820

20V 1N5817

MBR120P

SR102

MBR320

SR302

30V 1N5818

MBR130P

11DQ03

1N5821

MBR330

31DQ03

SR303

The following The following

diodes are all diodes are all

rated to 100V rated to 100V

SR103

40V 1N5819

MBR140P

11DQ04

IN5822

MBR340

31DQ04

SR304

11DF1

MUR110

HER102

31DF1

MURD310

HER302

SR104

50V MBR150

11DQ05

MBR350

31DQ05

SR305

SR105

60V MBR160

11DQ06

MBR360

31DQ06

SR306

SR106

FIGURE 8. Diode Selection Guide

Inductor

Code

Inductor

Value

Schott

Pulse Eng.

(Note 16)

PE-92108

PE-53113

PE-52626

PE-52627

PE-53114

PE-52629

PE-53115

PE-53116

PE-53117

PE-53118

PE-53119

PE-53120

PE-53121

PE-53122

Renco

(Note 17)

RL2444

RL1954

RL1953

RL1952

RL1951

RL1950

RL2445

RL2446

RL2447

RL1961

RL1960

RL1959

RL1958

RL2448

(Note 15)

L100

L150

L220

L330

L470

L680

H150

H220

H330

H470

H680

H1000

H1500

H2200

100 µH

150 µH

67127000

67127010

67127020

67127030

67127040

67127050

67127060

67127070

67127080

67127090

67127100

67127110

67127120

67127130

220 µH

330 µH

470 µH

680 µH

150 µH

220 µH

330 µH

470 µH

680 µH

1000 µH

1500 µH

2200 µH

Note 15: Schott Corp., (612) 475-1173, 1000 Parkers Lake Rd., Wayzata, MN 55391.

Note 16: Pulse Engineering, (619) 674-8100, P.O. Box 12236, San Diego, CA 92112.

Note 17: Renco Electronics Inc., (516) 586-5566, 60 Jeffryn Blvd. East, Deer Park, NY 11729.

FIGURE 9. Inductor Selection by Manufacturer’s Part Number

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16

pletely contained within the core, it generates more electro-

magnetic interference (EMI). This EMI can cause problems

in sensitive circuits, or can give incorrect scope readings

because of induced voltages in the scope probe.

Application Hints

INPUT CAPACITOR (C_IN

)

To maintain stability, the regulator input pin must be by-

passed with at least a 47 µF electrolytic capacitor. The

capacitor’s leads must be kept short, and located near the

regulator.

The inductors listed in the selection chart include ferrite pot

core construction for AIE, powdered iron toroid for Pulse

Engineering, and ferrite bobbin core for Renco.

An inductor should not be operated beyond its maximum

rated current because it may saturate. When an inductor

begins to saturate, the inductance decreases rapidly and the

inductor begins to look mainly resistive (the DC resistance of

the winding). This will cause the switch current to rise very

rapidly. Different inductor types have different saturation

characteristics, and this should be kept in mind when select-

ing an inductor.

If the operating temperature range includes temperatures

below −25˚C, the input capacitor value may need to be

larger. With most electrolytic capacitors, the capacitance

value decreases and the ESR increases with lower tempera-

tures and age. Paralleling a ceramic or solid tantalum ca-

pacitor will increase the regulator stability at cold tempera-

tures. For maximum capacitor operating lifetime, the

capacitor’s RMS ripple current rating should be greater than

The inductor manufacturer’s data sheets include current and

energy limits to avoid inductor saturation.

INDUCTOR RIPPLE CURRENT

When the switcher 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 voltage and output voltage, the peak-to-

peak amplitude of this inductor current waveform remains

constant. As the load current rises or falls, the entire saw-

tooth current waveform also rises or falls. The average DC

value of this waveform is equal to the DC load current (in the

buck regulator configuration).

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 regulator per-

formance and requirements.

If the load current drops to a low enough level, the bottom of

the sawtooth current waveform will reach zero, and the

switcher will change to a discontinuous mode of operation.

This is a perfectly acceptable mode of operation. Any buck

switching regulator (no matter how large the inductor value

is) will be forced to run discontinuous if the load current is

light enough.

The LM2575 (or any of the Simple Switcher family) can be

used for both continuous and discontinuous modes of opera-

tion.

OUTPUT CAPACITOR

An output capacitor is required to filter the output voltage and

is needed for loop stability. The capacitor should be located

near the LM2575 using short pc board traces. Standard

aluminum electrolytics are usually adequate, but low ESR

types are recommended for low output ripple voltage and

good stability. The ESR of a capacitor depends on many

factors, some which are: the value, the voltage rating, physi-

cal size and the type of construction. In general, low value or

low voltage (less than 12V) electrolytic capacitors usually

have higher ESR numbers.

The inductor value selection guides in Figure 3 through

Figure 7 were designed for buck regulator designs of the

continuous inductor current type. When using inductor val-

ues shown in the inductor selection guide, the peak-to-peak

inductor ripple current will be approximately 20% to 30% of

the maximum DC current. With relatively heavy load cur-

rents, the circuit operates in the continuous mode (inductor

current always flowing), but under light load conditions, the

circuit will be forced to the discontinuous mode (inductor

current falls to zero for a period of time). This discontinuous

mode of operation is perfectly acceptable. For light loads

(less than approximately 200 mA) it may be desirable to

operate the regulator in the discontinuous mode, primarily

because of the lower inductor values required for the discon-

tinuous mode.

The amount of output ripple voltage is primarily a function of

the ESR (Equivalent Series Resistance) of the output ca-

pacitor and the amplitude of the inductor ripple current

(∆I_IND). See the section on inductor ripple current in Applica-

tion Hints.

The lower capacitor values (220 µF–680 µF) will allow typi-

cally 50 mV to 150 mV of output ripple voltage, while larger-

value capacitors will reduce the ripple to approximately 20

mV to 50 mV.

The selection guide chooses inductor values suitable for

continuous mode operation, but if the inductor value chosen

is prohibitively high, the designer should investigate the

possibility of discontinuous operation. The computer design

software Switchers Made Simple will provide all component

values for discontinuous (as well as continuous) mode of

operation.

Output Ripple Voltage = (∆I_IND) (ESR of C_OUT

)

To further reduce the output ripple voltage, several standard

electrolytic capacitors may be paralleled, or a higher-grade

capacitor may be used. Such capacitors are often called

“high-frequency,” “low-inductance,” or “low-ESR.” These will

reduce the output ripple to 10 mV or 20 mV. However, when

operating in the continuous mode, reducing the ESR below

0.05Ω can cause instability in the regulator.

Inductors are available in different styles such as pot core,

toriod, E-frame, bobbin core, etc., as well as different core

materials, such as ferrites and powdered iron. The least

expensive, the bobbin core type, consists of wire wrapped

on a ferrite rod core. This type of construction makes for an

inexpensive inductor, but since the magnetic flux is not com-

17

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high-level TTL or CMOS signal. The ON /OFF pin can be

safely pulled up to +V_INwithout a resistor in series with it.

The ON /OFF pin should not be left open.

Application Hints (Continued)

Tantalum capacitors can have a very low ESR, and should

be carefully evaluated if it is the only output capacitor. Be-

cause of their good low temperature characteristics, a tan-

talum can be used in parallel with aluminum electrolytics,

with the tantalum making up 10% or 20% of the total capaci-

tance.

GROUNDING

To maintain output voltage stability, the power ground con-

nections must be low-impedance (see Figure 2). For the

TO-3 style package, the case is ground. For the 5-lead

TO-220 style package, both the tab and pin 3 are ground and

either connection may be used, as they are both part of the

same copper lead frame.

The capacitor’s ripple current rating at 52 kHz should be at

least 50% higher than the peak-to-peak inductor ripple cur-

rent.

With the N or M packages, all the pins labeled ground, power

ground, or signal ground should be soldered directly to wide

printed circuit board copper traces. This assures both low

inductance connections and good thermal properties.

CATCH DIODE

Buck regulators require a diode to provide a return path for

the inductor current when the switch is off. This diode should

be located close to the LM2575 using short leads and short

printed circuit traces.

HEAT SINK/THERMAL CONSIDERATIONS

In many cases, no heat sink is required to keep the LM2575

junction temperature within the allowed operating range. For

each application, to determine whether or not a heat sink will

be required, the following must be identified:

Because of their fast switching speed and low forward volt-

age drop, Schottky diodes provide the best efficiency, espe-

cially in low output voltage switching regulators (less than

5V). Fast-Recovery, High-Efficiency, or Ultra-Fast Recovery

diodes are also suitable, but some types with an abrupt

turn-off characteristic may cause instability and EMI prob-

lems. A fast-recovery diode with soft recovery characteristics

is a better choice. Standard 60 Hz diodes (e.g., 1N4001 or

1N5400, etc.) are also not suitable. See Figure 8 for Schot-

tky and “soft” fast-recovery diode selection guide.

1. Maximum ambient temperature (in the application).

2. Maximum regulator power dissipation (in application).

3. Maximum allowed junction temperature (150˚C for the

LM1575 or 125˚C for the LM2575). For a safe, conser-

vative design, a temperature approximately 15˚C cooler

than the maximum temperature should be selected.

4. LM2575 package thermal resistances θ_JAand θ_JC

.

OUTPUT VOLTAGE RIPPLE AND TRANSIENTS

Total power dissipated by the LM2575 can be estimated as

follows:

The output voltage of a switching power supply will contain a

sawtooth ripple voltage at the switcher frequency, typically

about 1% of the output voltage, and may also contain short

voltage spikes at the peaks of the sawtooth waveform.

P_D= (V_IN) (I_Q) + (V_O/V_IN) (I_LOAD) (V_SAT

)

where I_Q(quiescent current) and V_SATcan be found in the

Characteristic Curves shown previously, V_INis the applied

minimum input voltage, V_Ois the regulated output voltage,

and I_LOADis the load current. The dynamic losses during

turn-on and turn-off are negligible if a Schottky type catch

diode is used.

The output ripple voltage is due mainly to the inductor saw-

tooth ripple current multiplied by the ESR of the output

capacitor. (See the inductor selection in the application

hints.)

The voltage spikes are present because of the fast switching

action of the output switch, and the parasitic inductance of

the output filter capacitor. To minimize these voltage spikes,

special low inductance capacitors can be used, and their

lead lengths must be kept 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 no heat sink is used, the junction temperature rise can

be determined by the following:

∆T_J= (P_D) (θ_JA

)

To arrive at the actual operating junction temperature, add

the junction temperature rise to the maximum ambient tem-

perature.

T_J= ∆T_J+ T_A

An additional small LC filter (20 µH & 100 µF) can be added

to the output (as shown in Figure 15) to further reduce the

amount of output ripple and transients. A 10 x reduction in

output ripple voltage and transients is possible with this filter.

If the actual operating junction temperature is greater than

the selected safe operating junction temperature determined

in step 3, then a heat sink is required.

When using a heat sink, the junction temperature rise can be

determined by the following:

FEEDBACK CONNECTION

The LM2575 (fixed voltage versions) feedback pin must be

wired to the output voltage point of the switching power

supply. When using the adjustable version, physically locate

both output voltage programming resistors near the LM2575

to avoid picking up unwanted noise. Avoid using resistors

greater than 100 kΩ because of the increased chance of

noise pickup.

∆T_J= (P_D) (θ_JC+ θ_interface+ θ_{Heat sink}

The operating junction temperature will be:

T_J= T_A+ ∆T_J

As above, if the actual operating junction temperature is

greater than the selected safe operating junction tempera-

ture, then a larger heat sink is required (one that has a lower

thermal resistance).

)

ON /OFF INPUT

When using the LM2575 in the plastic DIP (N) or surface

mount (M) packages, several items about the thermal prop-

erties of the packages should be understood. The majority of

the heat is conducted out of the package through the leads,

with a minor portion through the plastic parts of the package.

For normal operation, the ON /OFF pin should be grounded

or driven with a low-level TTL voltage (typically below 1.6V).

To put the regulator into standby mode, drive this pin with a

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18

the available output current. Also, the start-up input current

of the buck-boost converter is higher than the standard

buck-mode regulator, and this may overload an input power

source with a current limit less than 1.5A. Using a delayed

turn-on or an undervoltage lockout circuit (described in the

next section) would allow the input voltage to rise to a high

enough level before the switcher would be allowed to turn

on.

Application Hints (Continued)

Since the lead frame is solid copper, heat from the die is

readily conducted through the leads to the printed circuit

board copper, which is acting as a heat sink.

For best thermal performance, the ground pins and all the

unconnected pins should be soldered to generous amounts

of printed circuit board copper, such as a ground plane.

Large areas of copper provide the best transfer of heat to the

surrounding air. Copper on both sides of the board is also

helpful in getting the heat away from the package, even if

there is no direct copper contact between the two sides.

Thermal resistance numbers as low as 40˚C/W for the SO

package, and 30˚C/W for the N package can be realized with

a carefully engineered pc board.

Because of the structural differences between the buck and

the buck-boost regulator topologies, the buck regulator de-

sign procedure section can not be used to select the inductor

or the output capacitor. The recommended range of inductor

values for the buck-boost design is between 68 µH and 220

µH, and the output capacitor values must be larger than what

is normally required for buck designs. Low input voltages or

high output currents require a large value output capacitor

(in the thousands of micro Farads).

Included on the Switchers Made Simple design software is

a more precise (non-linear) thermal model that can be used

to determine junction temperature with different input-output

parameters or different component values. It can also calcu-

late the heat sink thermal resistance required to maintain the

regulators junction temperature below the maximum operat-

ing temperature.

The peak inductor current, which is the same as the peak

switch current, can be calculated from the following formula:

Additional Applications

Where f_osc= 52 kHz. Under normal continuous inductor

current operating conditions, the minimum V_INrepresents

the worst case. Select an inductor that is rated for the peak

current anticipated.

INVERTING REGULATOR

Figure 10 shows a LM2575-12 in a buck-boost configuration

to generate a negative 12V output from a positive input

voltage. This circuit bootstraps the regulator’s ground pin to

the negative output voltage, then by grounding the feedback

pin, the regulator senses the inverted output voltage and

regulates it to −12V.

Also, the maximum voltage appearing across the regulator is

the absolute sum of the input and output voltage. For a −12V

output, the maximum input voltage for the LM2575 is +28V,

or +48V for the LM2575HV.

The Switchers Made Simple (version 3.3) design software

can be used to determine the feasibility of regulator designs

using different topologies, different input-output parameters,

different components, etc.

For an input voltage of 12V or more, the maximum available

output current in this configuration is approximately 0.35A. At

lighter loads, the minimum input voltage required drops to

approximately 4.7V.

The switch currents in this buck-boost configuration are

higher than in the standard buck-mode design, thus lowering

01147515

FIGURE 10. Inverting Buck-Boost Develops −12V

NEGATIVE BOOST REGULATOR

Because of the boosting function of this type of regulator, the

switch current is relatively high, especially at low input volt-

ages. Output load current limitations are a result of the

maximum current rating of the switch. Also, boost regulators

can not provide current limiting load protection in the event of

a shorted load, so some other means (such as a fuse) may

be necessary.

Another variation on the buck-boost topology is the negative

boost configuration. The circuit in Figure 11 accepts an input

voltage ranging from −5V to −12V and provides a regulated

−12V output. Input voltages greater than −12V will cause the

output to rise above −12V, but will not damage the regulator.

19

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Additional Applications (Continued)

01147517

01147516

Note: Complete circuit not shown.

Typical Load Current

Note: Pin numbers are for the TO-220 package.

200 mA for V = −5.2V

IN

500 mA for V = −7V

IN

Note: Pin numbers are for TO-220 package.

FIGURE 12. Undervoltage Lockout for Buck Circuit

FIGURE 11. Negative Boost

UNDERVOLTAGE LOCKOUT

In some applications it is desirable to keep the regulator off

until the input voltage reaches a certain threshold. An und-

ervoltage lockout circuit which accomplishes this task is

shown in Figure 12, while Figure 13 shows the same circuit

applied to a buck-boost configuration. These circuits keep

the regulator off until the input voltage reaches a predeter-

mined level.

V_TH≈ V_Z1+ 2V_BE(Q1)

01147518

DELAYED STARTUP

Note: Complete circuit not shown (see Figure 10).

The ON /OFF pin can be used to provide a delayed startup

feature as shown in Figure 14. With an input voltage of 20V

and for the part values shown, the circuit provides approxi-

mately 10 ms of delay time before the circuit begins switch-

ing. Increasing the RC time constant can provide longer

delay times. But excessively large RC time constants can

cause problems with input voltages that are high in 60 Hz or

120 Hz ripple, by coupling the ripple into the ON /OFF pin.

Note: Pin numbers are for the TO-220 package.

FIGURE 13. Undervoltage Lockout

for Buck-Boost Circuit

ADJUSTABLE OUTPUT, LOW-RIPPLE

POWER SUPPLY

A 1A power supply that features an adjustable output voltage

is shown in Figure 15. An additional L-C filter that reduces

the output ripple by a factor of 10 or more is included in this

circuit.

01147519

Note: Complete circuit not shown.

Note: Pin numbers are for the TO-220 package.

FIGURE 14. Delayed Startup

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20

Additional Applications (Continued)

01147520

Note: Pin numbers are for the TO-220 package.

FIGURE 15. 1.2V to 55V Adjustable 1A Power Supply with Low Output Ripple

Definition of Terms

BUCK REGULATOR

01147521

A switching regulator topology in which a higher voltage is

converted to a lower voltage. Also known as a step-down

switching regulator.

FIGURE 16. Simple Model of a Real Capacitor

Most standard aluminum electrolytic capacitors in the

100 µF–1000 µF range have 0.5Ω to 0.1Ω ESR. Higher-

grade capacitors (“low-ESR”, “high-frequency”, or “low-

inductance”’) in the 100 µF–1000 µF range generally have

ESR of less than 0.15Ω.

BUCK-BOOST REGULATOR

A switching regulator topology in which a positive voltage is

converted to a negative voltage without a transformer.

DUTY CYCLE (D)

Ratio of the output switch’s on-time to the oscillator period.

EQUIVALENT SERIES INDUCTANCE (ESL)

The pure inductance component of a capacitor (see Figure

16). The amount of inductance is determined to a large

extent on the capacitor’s construction. In a buck regulator,

this unwanted inductance causes voltage spikes to appear

on the output.

OUTPUT RIPPLE VOLTAGE

The AC component of the switching regulator’s output volt-

age. It is usually dominated by the output capacitor’s ESR

multiplied by the inductor’s ripple current (∆I_IND). The peak-

to-peak value of this sawtooth ripple current can be deter-

mined by reading the Inductor Ripple Current section of the

Application hints.

CATCH DIODE OR CURRENT STEERING DIODE

The diode which provides a return path for the load current

when the LM2575 switch is OFF.

EFFICIENCY (η)

The proportion of input power actually delivered to the load.

CAPACITOR RIPPLE CURRENT

RMS value of the maximum allowable alternating current at

which a capacitor can be operated continuously at a speci-

fied temperature.

STANDBY QUIESCENT CURRENT (I_STBY

)

CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)

Supply current required by the LM2575 when in the standby

mode (ON /OFF pin is driven to TTL-high voltage, thus

turning the output switch OFF).

The purely resistive component of a real capacitor’s imped-

ance (see Figure 16). It causes power loss resulting in

capacitor heating, which directly affects the capacitor’s op-

erating lifetime. When used as a switching regulator output

filter, higher ESR values result in higher output ripple volt-

ages.

INDUCTOR RIPPLE CURRENT (∆I_IND

)

The peak-to-peak value of the inductor current waveform,

typically a sawtooth waveform when the regulator is operat-

ing in the continuous mode (vs. discontinuous mode).

21

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nates. Inductor current is then limited only by the DC resis-

tance of the wire and the available source current.

Definition of Terms (Continued)

CONTINUOUS/DISCONTINUOUS MODE OPERATION

OPERATING VOLT MICROSECOND CONSTANT (E•T_op

)

Relates to the inductor current. In the continuous mode, the

inductor current is always flowing and never drops to zero,

vs. the discontinuous mode, where the inductor current

drops to zero for a period of time in the normal switching

cycle.

The product (in VoIt•µs) of the voltage applied to the inductor

and the time the voltage is applied. This E•T_opconstant is a

measure of the energy handling capability of an inductor and

is dependent upon the type of core, the core area, the

number of turns, and the duty cycle.

INDUCTOR SATURATION

The condition which exists when an inductor cannot hold any

more magnetic flux. When an inductor saturates, the induc-

tor appears less inductive and the resistive component domi-

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22

Physical Dimensions inches (millimeters)

unless otherwise noted

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

Order Number LM1575J-3.3/883, LM1575J-5.0/883,

LM1575J-12/883, LM1575J-15/883, or LM1575J-ADJ/883

NS Package Number J16A

14-Lead Wide Surface Mount (WM)

Order Number LM2575M-5.0, LM2575HVM-5.0, LM2575M-12,

LM2575HVM-12, LM2575M-15, LM2575HVM-15,

LM2575M-ADJ or LM2575HVM-ADJ

NS Package Number M24B

23

www.national.com

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

16-Lead Molded DIP (N)

Order Number LM2575N-5.0, LM2575HVN-5.0, LM2575N-12, LM2575HVN-12,

LM2575N-15, LM2575HVN-15, LM2575N-ADJ or LM2575HVN-ADJ

NS Package Number N16A

5-Lead TO-220 (T)

Order Number LM2575T-3.3, LM2575HVT-3.3, LM2575T-5.0, LM2575HVT-5.0, LM2575T-12,

LM2575HVT-12, LM2575T-15, LM2575HVT-15, LM2575T-ADJ or LM2575HVT-ADJ

NS Package Number T05A

www.national.com

24

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

TO-263, Molded, 5-Lead Surface Mount

Order Number LM2575S-3.3, LM2575HVS-3.3, LM2575S-5.0, LM2575HVS-5.0, LM2575S-12,

LM2575HVS-12, LM2575S-15, LM2575HVS-15, LM2575S-ADJ or LM2575HVS-ADJ

NS Package Number TS5B

25

www.national.com

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

Bent, Staggered 5-Lead TO-220 (T)

Order Number LM2575T-3.3 Flow LB03, LM2575HVT-3.3 Flow LB03,

LM2575T-5.0 Flow LB03, LM2575HVT-5.0 Flow LB03,

LM2575T-12 Flow LB03, LM2575HVT-12 Flow LB03,

LM2575T-15 Flow LB03, LM2575HVT-15 Flow LB03,

LM2575T-ADJ Flow LB03 or LM2575HVT-ADJ Flow LB03

NS Package Number T05D

LIFE SUPPORT POLICY

NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT

DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL

COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or

systems which, (a) are intended for surgical implant

into the body, or (b) support or sustain life, and

whose failure to perform when properly used in

accordance with instructions for use provided in the

labeling, can be reasonably expected to result in a

significant injury to the user.

2. A critical component is any component of a life

support device or system whose failure to perform

can be reasonably expected to cause the failure of

the life support device or system, or to affect its

safety or effectiveness.

BANNED SUBSTANCE COMPLIANCE

National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products

Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification

(CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2.

National Semiconductor

Americas Customer

Support Center

National Semiconductor

Europe Customer Support Center

Fax: +49 (0) 180-530 85 86

National Semiconductor

Asia Pacific Customer

Support Center

National Semiconductor

Japan Customer Support Center

Fax: 81-3-5639-7507

Email: new.feedback@nsc.com

Tel: 1-800-272-9959

Email: europe.support@nsc.com

Deutsch Tel: +49 (0) 69 9508 6208

English Tel: +44 (0) 870 24 0 2171

Français Tel: +33 (0) 1 41 91 8790

Email: ap.support@nsc.com

Email: jpn.feedback@nsc.com

Tel: 81-3-5639-7560

www.national.com

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.


型号：	LM2575HV3.3MWC
厂家：	National Semiconductor
描述：	IC 3.2 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, UUC, WAFER, Switching Regulator or Controller 开关
文件：	总27页 (文件大小：753K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LM2575HV3.3MWC [NSC]

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