LM1575J-CAD/883 [TI]

3.2A SWITCHING REGULATOR, 62kHz SWITCHING FREQ-MAX, CDIP16, CERDIP-16;


型号：	LM1575J-CAD/883
厂家：	TEXAS INSTRUMENTS
描述：	3.2A SWITCHING REGULATOR, 62kHz SWITCHING FREQ-MAX, CDIP16, CERDIP-16 CD 开关
文件：	总31页 (文件大小：670K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

National Semiconductor is now part of

Texas Instruments.

Search http://www.ti.com/ for the latest technical

information and details on our current products and services.

May 1999

LM1575/LM2575/LM2575HV Series

SIMPLE SWITCHER^®1A Step-Down Voltage Regulator

General Description

Features

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

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 Adjustable version output voltage range,

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

line and load conditions

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-regualtor 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

n Positive to negative converter (Buck-Boost)

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.

Typical Application (Fixed Output Voltage Versions)

DS011475-1

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

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

DS011475

www.national.com

Block Diagram and Typical Application

DS011475-2

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

Bent, Staggered Leads

5–Lead TO-22 (T)

5-Lead TO-220 (T)

DS011475-24

Side View

DS011475-22

DS011475-23

LM2575T-XX Flow LB03 or

LM2575HVT-XX Flow LB03

See NS Package Number T05D

Top View

LM2575T-XX or LM2575HVT-XX

See NS Package Number T05A

16–Lead DIP (N or J)

24-Lead Surface Mount (M)

DS011475-25

*No Internal Connection

Top View

DS011475-26

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

www.national.com

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

number.) (Continued)

TO-263(S)

5-Lead Surface-Mount Package

DS011475-29

Top View

DS011475-30

Side View

LM2575S-XX or LM2575HVS-XX

See NS Package Number TS5B

Ordering Information

Package

Type

NSC

Package

Number

T05A

Standard

Voltage Rating

(40V)

High

Voltage Rating

(60V)

Temperature

Range

5-Lead TO-220

Straight Leads

LM2575T-3.3

LM2575HVT-3.3

LM2575T-5.0

LM2575HVT-5.0

LM2575T-12

LM2575HVT-12

LM2575T-15

LM2575HVT-15

LM2575T-ADJ

LM2575HVT-ADJ

LM2575HVT-3.3 Flow LB03

LM2575HVT-5.0 Flow LB03

LM2575HVT-12 Flow LB03

LM2575HVT-15 Flow LB03

LM2575HVT-ADJ Flow LB03

LM2575HVN-5.0

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

LM2575N-5.0

Staggered Leads

16-Pin Molded

DIP

N16A

M24B

TS5B

−40˚C ≤ T_J≤ +125˚C

LM2575N-12

LM2575HVN-12

LM2575N-15

LM2575HVN-15

LM2575N-ADJ

LM2575HVN-ADJ

LM2575HVM-5.0

24-Pin

LM2575M-5.0

Surface Mount

LM2575M-12

LM2575HVM-12

LM2575M-15

LM2575HVM-15

LM2575M-ADJ

LM2575HVM-ADJ

LM2575HVS-3.3

5-Lead TO-236

Surface Mount

LM2575S-3.3

LM2575S-5.0

LM2575HVS-5.0

LM2575S-12

LM2575HVS-12

LM2575S-15

LM2575HVS-15

LM2575S-ADJ

LM2575HVS-ADJ

16-Pin Ceramic

DIP

J16A

LM1575J-3.3-QML

LM1575J-5.0-QML

LM1575J-12-QML

LM1575J-15-QML

LM1575J-ADJ-QML

−55˚C ≤ T_J≤ +150˚C

www.national.com

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

Operating Ratings

Temperature Range

LM1575

LM1575/LM2575

45V

63V

LM2575HV

ON /OFF Pin Input Voltage

Output Voltage to Ground

(Steady State)

−0.3V ≤ V ≤ +V_IN

−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_J25˚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

Output Voltage

V_IN12V, I_LOAD0.2A

3.3

Circuit of Figure 2

3.267

3.333

3.234

3.366

V(Min)

V(Max)

Output Voltage

4.75V ≤ V_IN≤ 40V, 0.2A ≤ I_LOAD≤ 1A

LM1575/LM2575

Circuit of Figure 2

3.200/3.168

3.400/3.432

3.168/3.135

3.432/3.465

V(Min)

V(Max)

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)

= =

V_IN12V, I_LOAD1A

Efficiency

LM1575-5.0, LM2575-5.0, LM2575HV-5.0

Electrical Characteristics

Specifications with standard type face are for T_J25˚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_IN12V, I_LOAD0.2A

5.0

Circuit of Figure 2

4.950

5.050

4.900

5.100

V(Min)

V(Max)

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)

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

= =

V_IN12V, I_LOAD1A

Efficiency

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LM1575-12, LM2575-12, LM2575HV-12

Electrical Characteristics

Specifications with standard type face are for T_J25˚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

Output Voltage

V_IN25V, I_LOAD0.2A

Circuit of Figure 2

11.88

12.12

11.76

12.24

V(Min)

V(Max)

Output Voltage

0.2A ≤ I_LOAD≤ 1A,

15V ≤ V_IN≤ 40V

Circuit of Figure 2

0.2A ≤ I_LOAD≤ 1A,

15V ≤ V_IN≤ 60V

Circuit of Figure 2

LM1575/LM2575

11.64/11.52

12.36/12.48

11.52/11.40

12.48/12.60

V(Min)

V(Max)

Output Voltage

LM2575HV

11.64/11.52

12.42/12.54

11.52/11.40

12.54/12.66

V(Min)

V(Max)

= =

V_IN15V, I_LOAD1A

Efficiency

LM1575-15, LM2575-15, LM2575HV-15

Electrical Characteristics

Specifications with standard type face are for T_J25˚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

Output Voltage

V_IN30V, I_LOAD0.2A

Circuit of Figure 2

14.85

15.15

14.70

15.30

V(Min)

V(Max)

Output Voltage

0.2A ≤ I_LOAD≤ 1A,

18V ≤ V_IN≤ 40V

Circuit of Figure 2

0.2A ≤ I_LOAD≤ 1A,

18V ≤ V_IN≤ 60V

Circuit of Figure 2

LM1575/LM2575

14.55/14.40

15.45/15.60

14.40/14.25

15.60/15.75

V(Min)

V(Max)

Output Voltage

LM2575HV

14.55/14.40

14.40/14.25

15.68/15.83

V(Min)

V(Max)

15.525/15.675

= =

V_IN18V, I_LOAD1A

Efficiency

LM1575-ADJ, LM2575-ADJ, LM2575HV-ADJ

Electrical Characteristics

Specifications with standard type face are for T_J25˚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

Feedback Voltage

V_IN12V, I_LOAD0.2A

1.230

V_OUT5V

1.217

1.243

1.217

1.243

V(Min)

V(Max)

Circuit of Figure 2

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LM1575-ADJ, LM2575-ADJ, LM2575HV-ADJ

Electrical Characteristics ^(Continued)

Specifications with standard type face are for T_J25˚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

Feedback Voltage

LM1575/LM2575

0.2A ≤ I_LOAD≤ 1A,

8V ≤ V_IN≤ 40V

1.230

1.205/1.193

1.255/1.267

1.193/1.180

1.267/1.280

V(Min)

V(Max)

V_OUT5V, Circuit of Figure 2

Feedback Voltage

LM2575HV

0.2A ≤ I_LOAD≤ 1A,

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_OUT5V, Circuit of Figure 2

= = =

V_IN12V, I_LOAD1A, V_OUT5V

Efficiency

All Output Voltage Versions

Electrical Characteristics

Specifications with standard type face are for T_J25˚C, and those with boldface type apply over full Operating Temperature

Range. Unless otherwise specified, V_IN12V for the 3.3V, 5V, and Adjustable version, V_IN25V for the 12V version, and V_IN

30V for the 15V version. I_LOAD200 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_OUT5V (Adjustable Version Only)

100/500

f_O

Oscillator Frequency

(Note 13)

kHz

kHz(Min)

kHz(Max)

47/43

58/62

47/42

58/63

V_SAT

Saturation Voltage

Max Duty Cycle (ON)

Current Limit

I_OUT1A (Note 5)

0.9

1.2/1.4

V(Max)

(Note 6)

%(Min)

I_CL

Peak Current (Notes 5, 13)

2.2

1.7/1.3

3.0/3.2

1.7/1.3

3.0/3.2

A(Min)

A(Max)

mA(Max)

Output 0V

I_L

Output Leakage

Current

(Notes 7, 8)

(Note 7)

Output −1V

7.5

Output −1V

mA(Max)

I_Q

Quiescent Current

10/12

mA(Max)

µA

I_STBY

Standby Quiescent

Current

ON /OFF Pin 5V (OFF)

200/500

200

µA(Max)

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

˚C/W

N Package, Junction to Ambient (Note 11)

M Package, Junction to Ambient (Note 11) 100

S Package, Junction to Ambient (Note 12)

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All Output Voltage Versions

Electrical Characteristics ^(Continued)

Specifications with standard type face are for T_J25˚C, and those with boldface type apply over full Operating Temperature

Range. Unless otherwise specified, V_IN12V for the 3.3V, 5V, and Adjustable version, V_IN25V for the 12V version, and V_IN

30V for the 15V version. I_LOAD200 mA.

Symbol Parameter

Conditions

Typ

LM1575-XX

LM2575-XX

LM2575HV-XX

Limit

Units

(Limits)

Limit

(Note 2)

(Note 3)

ON /OFF CONTROL Test Circuit Figure 2

V_IH

V_IL

I_IH

ON /OFF Pin Logic

Input Level

V_OUT0V

1.4

1.2

2.2/2.4

1.0/0.8

2.2/2.4

1.0/0.8

V(Min)

V(Max)

µA

V_OUTNominal Output Voltage

ON /OFF Pin 5V (OFF)

ON /OFF Pin Input

Current

µA(Max)

µA

I_IL

ON /OFF Pin 0V (ON)

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 in-

tended 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 limts are used to calculate Average Out-

going 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% pro-

duction 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.

40V (60V for the high voltage version).

Note 8:

Note 9: 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

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 soldered to a PC board

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

Note 11: Junction to ambient thermal resistance with approxmiately 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 JA 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.

Typical Performance Characteristics (Circuit of Figure 2)

Normalized Output Voltage

Line Regulation

Dropout Voltage

DS011475-34

DS011475-32

DS011475-33

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

Current Limit

Quiescent Current

Standby

Quiescent Current

DS011475-35

DS011475-36

DS011475-37

Oscillator Frequency

Switch Saturation

Voltage

Efficiency

DS011475-38

DS011475-40

DS011475-39

Minimum Operating Voltage

Quiescent Current

vs Duty Cycle

Feedback Voltage

vs Duty Cycle

DS011475-41

DS011475-42

DS011475-43

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

Feedback Pin Current

Maximum Power Dissipation

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

DS011475-5

DS011475-28

Switching Waveforms

Load Transient Response

DS011475-6

DS011475-7

OUT

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

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.

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

struction should be used for best results. When using the Ad-

justable version, physically locate the programming resistors

near the regulator, to keep the sensitive feedback wiring

short.

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Test Circuit and Layout Guidelines (Continued)

Fixed Output Voltage Versions

DS011475-8

—

100 µF, 75V, Aluminum Electrolytic

330 µF, 25V, Aluminum Electrolytic

—

OUT

—

Schottky, 11DQ06

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

Adjustable Output Voltage Version

DS011475-9

where V

REF

1.23V, R1 between 1k and 5k.

—

2k, 0.1%

6.12k, 0.1%

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

FIGURE 2.

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LM2575 Series Buck Regulator Design Procedure

PROCEDURE (Fixed Output Voltage Versions)

EXAMPLE (Fixed Output Voltage Versions)

Given:

V_OUT5V

V_OUTRegulated Output Voltage (3.3V, 5V, 12V, or 15V)

V_IN(Max) 20V

V_IN(Max) Maximum Input Voltage

I_LOAD(Max) Maximum Load Current

I_LOAD(Max) 0.8A

1. Inductor Selection (L1)

A. Select the correct Inductor value selection guide from Fig-

ures 3, 4, 5, 6 (Output voltages of 3.3V, 5V, 12V or 15V re-

spectively). For other output voltages, see the design proce-

dure for the adjustable version.

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 Fig-

ure 9, choose AIE 415-0926, Pulse Engineering PE-52627,

or RL1952.

B. From the inductor value selection guide, identify the in-

ductance 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 se-

lect 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 rat-

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

the inductor section in the Application Hints section of this

data sheet.

2. Output Capacitor Selection (C_OUT

)

2. Output Capacitor Selection (C_OUT)

A. C_OUT100 µF to 470 µF standard aluminum electrolytic.

A. The value of the output capacitor together with the induc-

tor 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 be-

tween 100 µF and 470 µF is recommended.

B. Capacitor voltage rating 20V.

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 rec-

ommended.

Higher voltage electrolytic capacitors generally have lower

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

select a capacitor rated for a higher voltage than would nor-

mally be needed.

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.

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.

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

1.25 times the maximum input voltage.

4. Input Capacitor (C_IN

)

4. Input Capacitor (C_IN)

An aluminum or tantalum electrolytic bypass capacitor lo-

cated close to the regulator is needed for stable operation.

A 47 µF, 25V aluminum electrolytic capacitor located near

the input and ground pins provides sufficient bypassing.

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(Continued)

INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation)

DS011475-12

DS011475-10

FIGURE 5. LM2575(HV)-12

FIGURE 3. LM2575(HV)-3.3

DS011475-13

DS011475-11

FIGURE 6. LM2575(HV)-15

FIGURE 4. LM2575(HV)-5.0

DS011475-14

FIGURE 7. LM2575(HV)-ADJ

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(Continued)

PROCEDURE (Adjustable Output Voltage Versions)

Given:

EXAMPLE (Adjustable Output Voltage Versions)

Given:

V_OUT10V

V_OUTRegulated Output Voltage

V_IN(Max) 25V

V_IN(Max) Maximum Input Voltage

I_LOAD(Max) 1A

I_LOAD(Max) Maximum Load Current

Switching Frequency (Fixed at 52 kHz)

52 kHz

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

1.Programming Output Voltage (Selecting R1 and R2)

shown in Figure 2 )

Use the following formula to select the appropriate resistor

values.

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

cient 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:

A. Calculate E • T (V • µs)

B. E • T 115 V • µs

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. I_LOAD(Max) 1A

D. Inductance Region H470

E. Inductor Value

470 µH Choose from AIE part

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

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

part #RL-1961.

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

value and the maximum load current value, and note the in-

ductor code for that region.

E. Identify the inductor value from the inductor code, and se-

lect 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 rat-

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

the inductor section in the application hints section of this

data sheet.

www.national.com

(Continued)

PROCEDURE (Adjustable Output Voltage Versions)

EXAMPLE (Adjustable Output Voltage Versions)

3. Output Capacitor Selection (C_OUT

)

3. Output Capacitor Selection (C_OUT

)

A. The value of the output capacitor together with the induc-

tor defines the dominate pole-pair of the switching regulator

loop. For stable operation, the capacitor must satisfy the fol-

lowing requirement:

However, for acceptable output ripple voltage select

C_OUT≥ 220 µF

C_OUT220 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 volt-

age, (approximately 1% of the output voltage) and transient

response, the output capacitor may need to be several times

larger than the above formula yields.

B. The capacitor’s voltage 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 generally have lower

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

select a capacitor rate for a higher voltage than would nor-

mally 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 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 selec-

tion guide in Figure 8.

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.

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

1.25 times the maximum input voltage.

5. Input Capacitor (C_IN

)

5. Input Capacitor (C_IN)

An aluminum or tantalum electrolytic bypass capacitor lo-

cated close to the regulator is needed for stable operation.

A 100 µF aluminum electrolytic capacitor located near the in-

put 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⁄

") dis-

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

www.national.com

(Continued)

V_R

Schottky

Fast Recovery

1A 3A

20V 1N5817

MBR120P

SR102

1N5820

MBR320

SR302

30V 1N5818

MBR130P

11DQ03

1N5821

MBR330

31DQ03

SR303

The following The following

diodes are

all

diodes are

all

SR103

rated to

100V

rated to

100V

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)

Renco

(Note 17)

RL2444

RL1954

RL1953

RL1952

RL1951

RL1950

RL2445

RL2446

RL2447

RL1961

RL1960

RL1959

RL1958

RL2448

(Note 15)

67127000

67127010

67127020

67127030

67127040

67127050

67127060

67127070

67127080

67127090

67127100

67127110

67127120

67127130

L100

L150

L220

L330

L470

L680

H150

H220

H330

H470

H680

H1000

H1500

H2200

100 µH

150 µH

220 µH

330 µH

470 µH

680 µH

150 µH

220 µH

330 µH

470 µH

680 µH

1000 µH

1500 µH

2200 µH

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

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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Application Hints

INPUT CAPACITOR (C_IN

)

in sensitive circuits, or can give incorrect scope readings be-

cause of induced voltages in the scope probe.

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

passed with at least a 47 µF electrolytic capacitor. The ca-

pacitor’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 En-

gineering, and ferrite bobbin core for Renco.

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

An inductor should not be operated beyond its maximum

rated current because it may saturate. When an inductor be-

gins 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.

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 saw-

tooth 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 con-

stant. As the load current rises or falls, the entire sawtooth

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

The inductor value selection guides in Figure 3 through Fig-

ure 7 were designed for buck regulator designs of the con-

tinuous inductor current type. When using inductor values

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

ductor ripple current will be approximately 20% to 30% of the

maximum DC current. With relatively heavy load currents,

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 discontinuous

mode.

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 alu-

minum 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, physical size

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

voltage (less than 12V) electrolytic capacitors usually have

higher ESR numbers.

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 selection guide chooses inductor values suitable for

continuous mode operation, but if the inductor value chosen

is prohibitively high, the designer should investigate the pos-

sibility of discontinuous operation. The computer design soft-

ware Switchers Made Simple will provide all component

values for discontinuous (as well as continuous) mode of op-

eration.

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 approxi-

mately 20 mV to 50 mV.

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 ex-

pensive, the bobbin core type, consists of wire wrapped on a

ferrite rod core. This type of construction makes for an inex-

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

pletely contained within the core, it generates more electro-

magnetic interference (EMI). This EMI can cause problems

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GROUNDING

Application Hints (Continued)

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.

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 tanta-

lum can be used in parallel with aluminum electrolytics, with

the tantalum making up 10% or 20% of the total capacitance.

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 in-

ductance 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, conserva-

tive design, a temperature approximately 15˚C cooler

than the maximum temperature should be selected.

4. LM2575 package thermal resistances θ_JAand θ_JC

Total power dissipated by the LM2575 can be estimated as

follows:

OUTPUT VOLTAGE RIPPLE AND TRANSIENTS

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

)

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.

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 di-

ode is used.

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

tooth ripple current multiplied by the ESR of the output ca-

pacitor. (See the inductor selection in the application hints.)

When no heat sink is used, the junction temperature rise can

be determined by the following:

The voltage spikes are present because of the the fast

switching action of the output switch, and the parasitic induc-

tance 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 evalu-

ate these transients, all contribute to the amplitude of these

spikes.

∆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

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.

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.

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

determined by the following:

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

)

FEEDBACK CONNECTION

The operating junction temperature will be:

The LM2575 (fixed voltage versions) feedback pin must be

wired to the output voltage point of the switching power sup-

ply. 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_JT_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).

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.

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.

ON /OFF INPUT

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

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.

For best thermal performance, the ground pins and all the

unconnected pins should be soldered to generous amounts

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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)

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 to select the in-

ductor 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

INVERTING REGULATOR

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

to generate a negative 12V output from a positive input volt-

age. 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 regu-

lates it to −12V.

Where f_osc52 kHz. Under normal continuous inductor cur-

rent operating conditions, the minimum V_INrepresents the

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

rent anticipated.

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.

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 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.

The switch currents in this buck-boost configuration are

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

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

DS011475-15

FIGURE 10. Inverting Buck-Boost Develops −12V

NEGATIVE BOOST REGULATOR

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.

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 maxi-

mum 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.

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Additional Applications (Continued)

DS011475-17

DS011475-16

Note: Complete circuit not shown.

Typical Load Current

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

200 mA for V

500 mA for V

−5.2V

−7V

FIGURE 12. Undervoltage Lockout for Buck Circuit

Note: Pin numbers are for TO-220 package.

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 under-

voltage 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 regu-

lator off until the input voltage reaches a predetermined

level.

V_TH≈ V_Z1+ 2V_BE(Q1)

DELAYED STARTUP

DS011475-18

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 de-

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

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.

DS011475-19

Note: Complete circuit not shown.

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

FIGURE 14. Delayed Startup

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Additional Applications (Continued)

DS011475-20

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

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

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.

Definition of Terms

BUCK REGULATOR

A switching regulator topology in which a higher voltage is

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

switching regulator.

EQUIVALENT SERIES INDUCTANCE (ESL)

The pure inductance component of a capacitor (see Figure

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

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

unwanted inductance causes voltage spikes to appear on

the output.

BUCK-BOOST REGULATOR

A switching regulator topology in which a positive voltage is

converted to a negative voltage without a transformer.

OUTPUT RIPPLE VOLTAGE

DUTY CYCLE (D)

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 de-

termined by reading the Inductor Ripple Current section of

the Application hints.

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

CAPACITOR RIPPLE CURRENT

RMS value of the maximum allowable alternating current at

which a capacitor can be operated continuously at a speci-

fied temperature.

CATCH DIODE OR CURRENT STEERING DIODE

The diode which provides a return path for the load current

when the LM2575 switch is OFF.

STANDBY QUIESCENT CURRENT (I_STBY

)

Supply current required by the LM2575 when in the standby

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

ing the output switch OFF).

EFFICIENCY (η)

The proportion of input power actually delivered to the load.

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).

CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)

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

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

pacitor heating, which directly affects the capacitor’s operat-

ing lifetime. When used as a switching regulator output filter,

higher ESR values result in higher output ripple voltages.

CONTINUOUS/DISCONTINUOUS MODE OPERATION

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.

DS011475-21

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.

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OPERATING VOLT MICROSECOND CONSTANT (E•T_op

)

Definition of Terms (Continued)

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 num-

ber 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-

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

tance of the wire and the available source current.

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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

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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

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

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

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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.

National Semiconductor

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Tel: 1-800-272-9959

Fax: 1-800-737-7018

Email: support@nsc.com

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National Semiconductor

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Response Group

Tel: 65-2544466

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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.

National Semiconductor Company

Design

Purchasing Quality Company Jobs

Products > Analog - Regulators > Simple Switchers > LM1575

Product Folder

LM1575

SIMPLE SWITCHER 1A Step-Down Voltage Regulator

Generic P/N 1575

Contents

Parametric Table

Multiple Output Capability

On/Off Pin

General Description

Features

Applications

Datasheet

Package Availability, Models, Samples

& Pricing

Yes

Input Voltage, min (Volt)

Input Voltage, max (Volt)

Output Current, max

1 Amp

Output Voltage (Volt)

Design Tools

Adjustable Output Voltage

Switching Frequency (Hz)

52000

Adjustable Switching Frequency No

Sync Pin

Efficiency (%)

Inverting

Yes

Step-down

General Description

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 available in fixed output voltages of

3.3V, 5V, 12V, 15V, and an adjustable output version.

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 reduces 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.

Other features include a guaranteed ±4% tolerance on output voltage within specified input

voltages and output load conditions, and ±10% on the oscillator frequency. External

shutdown is included, featuring 50 µA (typical) standby current. The output switch includes

cycle-by-cycle current limiting, as well as thermal shutdown for full protection under fault

conditions.

Features

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

Adjustable version output voltage range, 1.23V to 37V (57V for HV version) ±4%

max over line and load conditions

Guaranteed 1A output current

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

Requires only 4 external components

52 kHz fixed frequency internal oscillator

TTL shutdown capability, low power standby mode

High efficiency

Uses readily available standard inductors

Thermal shutdown and current limit protection

P Product Enhancement tested

Applications

Simple high-efficiency step-down (buck) regulator

Efficient pre-regualtor for linear regulators

On-card switching regulators

Positive to negative converter (Buck-Boost)

Datasheet

Size

(in

Kbytes)

Title

Date

Receive via

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Online

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LM1575/LM2575/LM2575HV Series SIMPLE SWITCHER 1A Step-Down Voltage

Regulator

1-Jun- View

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609 Kbytes

248 Kbytes

243 Kbytes

248 Kbytes

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LM1575 Mil-Aero Datasheet MNLM1575-12-X

LM1575 Mil-Aero Datasheet MNLM1575-15-X

LM1575 Mil-Aero Datasheet MNLM1575-5.0-X

LM1575 Mil-Aero Datasheet MNLM1575-ADJ-X

View

Online

Receive via

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Online

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View

Online

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Please use Adobe Acrobat to view PDF file(s).

If you have trouble printing, see Printing Problems.

Package Availability, Models, Samples & Pricing

Samples

Electronic

Orders

Package

Type

Models

Budgetary Pricing

Quantity $US each

Std

Pack

Size

Package

Marking

Part Number

Status

# pins

SPICE IBIS

tube

N/A

[logo]¢Z¢S¢4¢A$E

LM1575J-C5

/883C

LM1575J-C5/883

LM1575J-CAD/883

5962-9167301QEA

Cerdip

Lifetime buy

N/A N/A

tube

N/A

[logo]¢Z¢S¢4¢A$E

LM1575J-CAD/883Q¢M

tube

$9.3500 of

[logo]¢Z¢S¢4¢A$E

LM1575J-12-QML

5962-9167301QEA

16 Full production N/A N/A

25+

tube

$9.3500 of

[logo]¢Z¢S¢4¢A$E

LM1575J-15-QML

5962-9167401QEA

5962-9167201QEA

Cerdip

16 Full production N/A N/A

25+

tube

$9.3500 of

[logo]¢Z¢S¢4¢A$E

LM1575J-5.0-QML

5962-9167201QEA

[logo]¢Z¢S¢4¢A$E

LM1575WG12-

QML 5962-

tray

N/A

LM1575WG12-QML Ceramic SOIC 16

Preliminary

N/A N/A

9167301QZA

[logo]¢Z¢S¢4¢A$E

LM1575WG15-

QML 5962-

tray

N/A

LM1575WG15-QML Ceramic SOIC 16

LM1575WG5.0-MPR Ceramic SOIC 16

LM1575WG5.0-QML Ceramic SOIC 16

Preliminary

N/A N/A

9167401QZA

tray

N/A

[logo]¢Z¢S¢4¢A$E

LM1575WG5.0

-MPR PROTO

[logo]¢Z¢S¢4¢A$E

LM1575WG5.0-

QML 5962-

tray

N/A

9167201QZA

[logo]¢Z¢S¢4¢A$E

LM1575WGADJ-

QML 5962-

tray

N/A

LM1575WGADJ-QML Ceramic SOIC 16

Preliminary

N/A N/A

9167101QZA

tube

N/A

[logo]¢Z¢S¢4¢A$E

LM1575J-5.0-MPR

PROTO

LM1575J-5.0-MPR

Cerdip

Design Tools

Size

(in Kbytes)

Title

Date

Receive via Email

Download

View Online

SimpleSwitcher® DC-DC Converters Design Software 4 Kbytes

12-Jul-2000

View

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[Information as of 2-Sep-2000]

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LM1575J-CAD/883 [TI]

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