National Semiconductor [object Object], LM2575-3.3, LM1575-3.3, LM2575HV-3.3, LM1575-5.0 Series Manual

LM1575/LM2575/LM2575HV
SIMPLE SWITCHER

®

1A Step-Down Voltage Regulator

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

August 2004

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
put voltage within specified input voltages and output load
conditions, and
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.

±

10% on the oscillator frequency. External

4% tolerance on out-

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)
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

±

4% max over

Applications

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

Typical Application (Fixed Output Voltage

Versions)

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

01147501

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

© 2004 National Semiconductor Corporation DS011475 www.national.com

Block Diagram and Typical Application

LM1575/LM2575/LM2575HV

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.

Connection Diagrams

number.)

Straight Leads

5–Lead TO-220 (T)

01147522

Top View

LM2575T-XX or LM2575HVT-XX

See NS Package Number T05A

01147502

FIGURE 1.

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

Bent, Staggered Leads

5-Lead TO-220 (T)

01147524

Top View

01147523

Side View
LM2575T-XX Flow LB03 or
LM2575HVT-XX Flow LB03

See NS Package Number T05D

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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)

LM1575/LM2575/LM2575HV

*No Internal Connection

Top View

LM2575N-XX or LM2575HVN-XX

See NS Package Number N16A

LM1575J-XX-QML

See NS Package Number J16A

01147525

01147526

*No Internal Connection

Top View

LM2575M-XX or LM2575HVM-XX

See NS Package Number M24B

TO-263(S)

5-Lead Surface-Mount Package

Top View

01147529

Side View

01147530

LM2575S-XX or LM2575HVS-XX
See NS Package Number TS5B

Ordering Information

Package NSC Standard High Temperature

Type Package Voltage Rating Voltage Rating Range

Number (40V) (60V)

5-Lead TO-220 T05A LM2575T-3.3 LM2575HVT-3.3

Straight Leads LM2575T-5.0 LM2575HVT-5.0

LM2575T-12 LM2575HVT-12

LM2575T-15 LM2575HVT-15

LM2575T-ADJ LM2575HVT-ADJ

5-Lead TO-220 T05D LM2575T-3.3 Flow LB03 LM2575HVT-3.3 Flow LB03

Bent and LM2575T-5.0 Flow LB03 LM2575HVT-5.0 Flow LB03

Staggered Leads LM2575T-12 Flow LB03 LM2575HVT-12 Flow LB03

LM2575T-15 Flow LB03 LM2575HVT-15 Flow LB03

LM2575T-ADJ Flow LB03 LM2575HVT-ADJ Flow LB03

www.national.com3

Ordering Information (Continued)

Package NSC Standard High Temperature

Type Package Voltage Rating Voltage Rating Range

Number (40V) (60V)

16-Pin Molded N16A LM2575N-5.0 LM2575HVN-5.0 −40˚C ≤ T

DIP LM2575N-12 LM2575HVN-12

LM2575N-15 LM2575HVN-15

LM2575N-ADJ LM2575HVN-ADJ

24-Pin M24B LM2575M-5.0 LM2575HVM-5.0

LM1575/LM2575/LM2575HV

Surface Mount LM2575M-12 LM2575HVM-12

LM2575M-15 LM2575HVM-15

LM2575M-ADJ LM2575HVM-ADJ

5-Lead TO-263 TS5B LM2575S-3.3 LM2575HVS-3.3

Surface Mount LM2575S-5.0 LM2575HVS-5.0

LM2575S-12 LM2575HVS-12

LM2575S-15 LM2575HVS-15

LM2575S-ADJ LM2575HVS-ADJ

16-Pin Ceramic J16A LM1575J-3.3-QML

DIP LM1575J-5.0-QML

LM1575J-12-QML −55˚C ≤ T

LM1575J-15-QML

LM1575J-ADJ-QML

≤ +125˚C

J

≤ +150˚C

J

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LM1575/LM2575/LM2575HV

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)2kV

Lead Temperature

(Soldering, 10 sec.) 260˚C

Maximum Supply Voltage

LM1575/LM2575 45V

Operating Ratings

LM2575HV 63V

ON /OFF Pin Input Voltage

−0.3V ≤ V ≤ +V

Output Voltage to Ground

(Steady State) −1V

Power Dissipation Internally Limited

Storage Temperature Range −65˚C to +150˚C

Maximum Junction Temperature 150˚C

IN

Temperature Range

LM1575 −55˚C ≤ T

LM2575/LM2575HV −40˚C ≤ T

≤ +150˚C

J

≤ +125˚C

J

Supply Voltage

LM1575/LM2575 40V

LM2575HV 60V

LM1575-3.3, LM2575-3.3, LM2575HV-3.3 Electrical Characteristics

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

Symbol Parameter Conditions Typ LM1575-3.3 LM2575-3.3 Units

(Limits)

SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2

V

OUT

Output Voltage VIN= 12V, I

LOAD

Circuit of Figure 2 3.267 3.234 V(Min)

V

OUT

Output Voltage 4.75V ≤ VIN≤ 40V, 0.2A ≤ I

LM1575/LM2575 Circuit of Figure 2 3.200/3.168 3.168/3.135 V(Min)

V

OUT

Output Voltage 4.75V ≤ VIN≤ 60V, 0.2A ≤ I

LM2575HV Circuit of Figure 2 3.200/3.168 3.168/3.135 V(Min)

η Efficiency V

= 12V, I

IN

LOAD

LM2575HV-3.3

Limit Limit

(Note 2) (Note 3)

= 0.2A 3.3 V

3.333 3.366 V(Max)

≤ 1A 3.3 V

LOAD

3.400/3.432 3.432/3.465 V(Max)

≤ 1A 3.3 V

LOAD

3.416/3.450 3.450/3.482 V(Max)

=1A 75 %

LM1575-5.0, LM2575-5.0, LM2575HV-5.0 Electrical Characteristics

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

Symbol Parameter Conditions Typ LM1575-5.0 LM2575-5.0 Units

(Limits)

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SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2

V

OUT

Output Voltage VIN= 12V, I

LOAD

Circuit of Figure 2 4.950 4.900 V(Min)

V

OUT

Output Voltage 0.2A ≤ I

LM1575/LM2575 8V ≤ V

≤ 1A, 5.0 V

LOAD

≤ 40V 4.850/4.800 4.800/4.750 V(Min)

IN

Circuit of Figure 2 5.150/5.200 5.200/5.250 V(Max)

V

OUT

Output Voltage 0.2A ≤ I

LM2575HV 8V ≤ V

≤ 1A, 5.0 V

LOAD

≤ 60V 4.850/4.800 4.800/4.750 V(Min)

IN

Circuit of Figure 2 5.175/5.225 5.225/5.275 V(Max)

LM2575HV-5.0

Limit Limit

(Note 2) (Note 3)

= 0.2A 5.0 V

5.050 5.100 V(Max)

LM1575-5.0, LM2575-5.0, LM2575HV-5.0

= 12V, I

IN

(Continued)

=1A 77 %

LOAD

LM2575HV-5.0

Limit Limit

(Note 2) (Note 3)

Electrical Characteristics

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

Symbol Parameter Conditions Typ LM1575-5.0 LM2575-5.0 Units

η Efficiency V

LM1575/LM2575/LM2575HV

LM1575-12, LM2575-12, LM2575HV-12 Electrical Characteristics

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

Symbol Parameter Conditions Typ LM1575-12 LM2575-12 Units

LM2575HV-12

Limit Limit

(Note 2) (Note 3)

SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2

V

OUT

V

OUT

Output Voltage VIN= 25V, I

Output Voltage 0.2A ≤ I

LM1575/LM2575 15V ≤ V

V

OUT

Output Voltage 0.2A ≤ I

LM2575HV 15V ≤ V

η Efficiency V

Circuit of Figure 2 11.88 11.76 V(Min)

LOAD

IN

Circuit of Figure 2 12.36/12.48 12.48/12.60 V(Max)

LOAD

IN

Circuit of Figure 2 12.42/12.54 12.54/12.66 V(Max)

= 15V, I

IN

= 0.2A 12 V

LOAD

12.12 12.24 V(Max)

≤ 1A, 12 V

≤ 40V 11.64/11.52 11.52/11.40 V(Min)

≤ 1A, 12 V

≤ 60V 11.64/11.52 11.52/11.40 V(Min)

=1A 88 %

LOAD

(Limits)

(Limits)

LM1575-15, LM2575-15, LM2575HV-15 Electrical Characteristics

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

Symbol Parameter Conditions Typ LM1575-15 LM2575-15 Units

(Limits)

SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2

V

OUT

Output Voltage VIN= 30V, I

LOAD

Circuit of Figure 2 14.85 14.70 V(Min)

V

OUT

Output Voltage 0.2A ≤ I

LM1575/LM2575 18V ≤ V

≤ 1A, 15 V

LOAD

≤ 40V 14.55/14.40 14.40/14.25 V(Min)

IN

Circuit of Figure 2 15.45/15.60 15.60/15.75 V(Max)

V

OUT

Output Voltage 0.2A ≤ I

LM2575HV 18V ≤ V

≤ 1A, 15 V

LOAD

≤ 60V 14.55/14.40 14.40/14.25 V(Min)

IN

Circuit of Figure 2 15.525/15.675 15.68/15.83 V(Max)

η Efficiency V

= 18V, I

IN

LOAD

LM2575HV-15

Limit Limit

(Note 2) (Note 3)

= 0.2A 15 V

15.15 15.30 V(Max)

=1A 88 %

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LM1575-ADJ, LM2575-ADJ, LM2575HV-ADJ Electrical Characteristics

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

Symbol Parameter Conditions Typ LM1575-ADJ LM2575-ADJ Units

LM2575HV-ADJ

(Limits)

Limit Limit

(Note 2) (Note 3)

SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2

V

OUT

Feedback Voltage VIN= 12V, I

V

= 5V 1.217 1.217 V(Min)

OUT

= 0.2A 1.230 V

LOAD

Circuit of Figure 2 1.243 1.243 V(Max)

V

OUT

V

OUT

η Efficiency V

Feedback Voltage 0.2A ≤ I

LM1575/LM2575 8V ≤ V

V

OUT

Feedback Voltage 0.2A ≤ I

LM2575HV 8V ≤ V

V

OUT

= 12V, I

IN

≤ 1A, 1.230 V

LOAD

≤ 40V 1.205/1.193 1.193/1.180 V(Min)

IN

= 5V, Circuit of Figure 2 1.255/1.267 1.267/1.280 V(Max)

≤ 1A, 1.230 V

LOAD

≤ 60V 1.205/1.193 1.193/1.180 V(Min)

IN

= 5V, Circuit of Figure 2 1.261/1.273 1.273/1.286 V(Max)

LOAD

= 1A, V

=5V 77 %

OUT

All Output Voltage Versions Electrical Characteristics

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

and V

= 30V for the 15V version. I

IN

LOAD

Symbol Parameter Conditions Typ LM1575-XX LM2575-XX Units

DEVICE PARAMETERS

I

b

f

O

V

SAT

Feedback Bias Current V

OUT

Oscillator Frequency (Note 13) 52 kHz

Saturation Voltage I

OUT

DC Max Duty Cycle (ON) (Note 6) 98 %

I

CL

I

L

Current Limit Peak Current (Notes 5, 13) 2.2 A

Output Leakage (Notes 7, 8) Output = 0V 2 2 mA(Max)

Current Output = −1V 7.5 mA

I

Q

I

STBY

Quiescent Current (Note 7) 5 mA

Standby Quiescent ON /OFF Pin = 5V (OFF) 50 µA

Current 200/500 200 µA(Max)

= 12V for the 3.3V, 5V, and Adjustable version, VIN= 25V for the 12V version,

IN

= 200 mA.

LM2575HV-XX

(Limits)

Limit Limit

(Note 2) (Note 3)

= 5V (Adjustable Version Only) 50 100/500 100/500 nA

47/43 47/42 kHz(Min)

58/62 58/63 kHz(Max)

= 1A (Note 5) 0.9 V

1.2/1.4 1.2/1.4 V(Max)

93 93 %(Min)

1.7/1.3 1.7/1.3 A(Min)

3.0/3.2 3.0/3.2 A(Max)

Output = −1V 30 30 mA(Max)

10/12 10 mA(Max)

LM1575/LM2575/LM2575HV

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All Output Voltage Versions
Electrical Characteristics

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

and V

Symbol Parameter Conditions Typ LM1575-XX LM2575-XX Units

LM1575/LM2575/LM2575HV

DEVICE PARAMETERS

θ

JA

θ

JA

θ

JC

θ

JA

θ

JA

θ

JA

ON /OFF CONTROL Test Circuit Figure 2

V

IH

V

IL

I

IH

I

IL

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

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

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
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

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.

= 30V for the 15V version. I

IN

Thermal Resistance T Package, Junction to Ambient (Note 9) 65

T Package, Junction to Ambient (Note 10) 45 ˚C/W

T Package, Junction to Case 2

N Package, Junction to Ambient (Note 11) 85

M Package, Junction to Ambient (Note 11) 100

S Package, Junction to Ambient (Note 12) 37

ON /OFF Pin Logic V

Input Level V

OUT

OUT

ON /OFF Pin Input ON /OFF Pin = 5V (OFF) 12 µA

Current 30 30 µA(Max)

ON /OFF Pin = 0V (ON) 0µA

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

IN

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

JA

(Continued)

= 12V for the 3.3V, 5V, and Adjustable version, VIN= 25V for the 12V version,

IN

= 200 mA.

LOAD

LM2575HV-XX

Limit Limit

(Note 2) (Note 3)

= 0V 1.4 2.2/2.4 2.2/2.4 V(Min)

= Nominal Output Voltage 1.2 1.0/0.8 1.0/0.8 V(Max)

10 10 µA(Max)

1

⁄2inch leads in a socket, or on a PC

1

⁄2inch leads soldered to a PC board

(Limits)

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Typical Performance Characteristics (Circuit of Figure 2)

Normalized Output Voltage Line Regulation

01147532 01147533

Dropout Voltage Current Limit

LM1575/LM2575/LM2575HV

Quiescent Current

01147534

01147535

Standby

Quiescent Current

01147536 01147537

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

Oscillator Frequency

LM1575/LM2575/LM2575HV

Switch Saturation

Voltage

01147538

Efficiency Minimum Operating Voltage

01147540

Quiescent Current

vs Duty Cycle

Feedback Voltage

vs Duty Cycle

01147539

01147541

01147542 01147543

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

Maximum Power Dissipation

Feedback Pin Current

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

LM1575/LM2575/LM2575HV

01147505

Switching Waveforms Load Transient Response

V

=5V

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

01147506

Test Circuit and Layout Guidelines

As in any switching regulator, layout is very important. Rap­idly 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.

01147528

01147507

Single-point grounding (as indicated) or ground plane con­struction should be used for best results. When using the
Adjustable 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

LM1575/LM2575/LM2575HV

CIN— 100 µF, 75V, Aluminum Electrolytic

— 330 µF, 25V, Aluminum Electrolytic

C

OUT

D1 — Schottky, 11DQ06

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

Adjustable Output Voltage Version

where V

R1 — 2k, 0.1%

R2 — 6.12k, 0.1%

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

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

REF

01147508

01147509

FIGURE 2.

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LM2575 Series Buck Regulator Design Procedure

PROCEDURE (Fixed Output Voltage Versions) EXAMPLE (Fixed Output Voltage Versions)

Given: V

15V) V
Maximum Load Current

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

I

LOAD

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

information, see the inductor section in the Application Hints

2. Output Capacitor Selection (C

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

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

4. Input Capacitor (C

electrolytic bypass capacitor located close to the regulator is

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

OUT

(Max) = Maximum Input Voltage I

IN

(Max) =

LOAD

(Max) and

IN

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

. For additional inductor

LOAD

section of this data sheet.

)A.The value of the

OUT

normally be needed.

maximum input voltage.

) An aluminum or tantalum

IN

needed for stable operation.

Given: V

=5VVIN(Max) = 20V I

OUT

LOAD

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.C

to 470 µF standard aluminum electrolytic. B. Capacitor

voltage rating = 20V.

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

) A 47 µF, 25V aluminum electrolytic

IN

capacitor located near the input and ground pins provides
sufficient bypassing.

(Max) = 0.8A

= 100 µF

OUT

LM1575/LM2575/LM2575HV

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Inductor Value Selection Guides (For Continuous Mode Operation)

LM1575/LM2575/LM2575HV

FIGURE 3. LM2575(HV)-3.3

FIGURE 4. LM2575(HV)-5.0

01147510

01147511

01147512

FIGURE 5. LM2575(HV)-12

01147513

FIGURE 6. LM2575(HV)-15

FIGURE 7. LM2575(HV)-ADJ

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01147514

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

PROCEDURE (Adjustable Output Voltage Versions) EXAMPLE (Adjustable Output Voltage Versions)

Given: V

Maximum Input Voltage I

= Regulated Output Voltage VIN(Max) =

OUT

(Max) = Maximum Load

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.

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

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

Given: V

= 10V VIN(Max) = 25V I

OUT

(Max) = 1A F =

LOAD

52 kHz

1.Programming Output Voltage (Selecting R1 and R2)

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

LM1575/LM2575/LM2575HV

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

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

formula:

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 hori­zontal 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 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
the inductor section in the application hints section of this data

. For additional inductor information, see

LOAD

sheet.

3. Output Capacitor Selection (C

)A.The value of the

OUT

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:

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 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 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

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.

2. Inductor Selection (L1) A. Calculate E

•

B. E•T = 115 V•µs C. I

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

(Max) = 1A D. Inductance

LOAD

•

part #430-0634, Pulse Engineering part #PE-53118, or
Renco part #RL-1961.

3. Output Capacitor Selection (C

OUT

)A.

However, for acceptable output ripple voltage select C

220 µF C

= 220 µF electrolytic capacitor

OUT

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.

T(V•µs)

OUT

≥

www.national.com15

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

PROCEDURE (Adjustable Output Voltage Versions) EXAMPLE (Adjustable Output Voltage Versions)

5. Input Capacitor (C

electrolytic bypass capacitor located close to the regulator is

needed for stable operation.

) An aluminum or tantalum

IN

5. Input Capacitor (CIN) 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 (3
diskette for IBM compatible computers from a National Semiconductor sales office in your area.

LM1575/LM2575/LM2575HV

1

⁄2")

www.national.com 16

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

LM1575/LM2575/LM2575HV

V

R

Schottky Fast Recovery

1A 3A 1A 3A

20V 1N5817 1N5820

MBR120P MBR320

SR102 SR302

30V 1N5818 1N5821

MBR130P MBR330 The following

11DQ03 31DQ03

SR103 SR303

diodes are all
rated to 100V

The following
diodes are all

rated to 100V

40V 1N5819 IN5822

MBR140P MBR340

11DQ04 31DQ04

SR104 SR304

11DF1
MUR110
HER102

31DF1

MURD310

HER302

50V MBR150 MBR350

11DQ05 31DQ05

SR105 SR305

60V MBR160 MBR360

11DQ06 31DQ06

SR106 SR306

FIGURE 8. Diode Selection Guide

Inductor Inductor Schott Pulse Eng. Renco

Code Value (Note 15) (Note 16) (Note 17)

L100 100 µH 67127000 PE-92108 RL2444

L150 150 µH 67127010 PE-53113 RL1954

L220 220 µH 67127020 PE-52626 RL1953

L330 330 µH 67127030 PE-52627 RL1952

L470 470 µH 67127040 PE-53114 RL1951

L680 680 µH 67127050 PE-52629 RL1950

H150 150 µH 67127060 PE-53115 RL2445

H220 220 µH 67127070 PE-53116 RL2446

H330 330 µH 67127080 PE-53117 RL2447

H470 470 µH 67127090 PE-53118 RL1961

H680 680 µH 67127100 PE-53119 RL1960

H1000 1000 µH 67127110 PE-53120 RL1959

H1500 1500 µH 67127120 PE-53121 RL1958

H2200 2200 µH 67127130 PE-53122 RL2448

Note 15: Schott Corp., [phone], 1000 Parkers Lake Rd., Wayzata, MN 55391.

Note 16: Pulse Engineering, [phone], P.O. Box 12236, San Diego, CA 92112.

Note 17: Renco Electronics Inc., [phone], 60 Jeffryn Blvd. East, Deer Park, NY 11729.

FIGURE 9. Inductor Selection by Manufacturer’s Part Number

www.national.com17

Application Hints

INPUT CAPACITOR (CIN)

To maintain stability, the regulator input pin must be by­passed with at least a 47 µF electrolytic capacitor. The
capacitor’s leads must be kept short, and located near the
regulator.

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-

LM1575/LM2575/LM2575HV

tures and age. Paralleling a ceramic or solid tantalum ca­pacitor will increase the regulator stability at cold tempera­tures. For maximum capacitor operating lifetime, the
capacitor’s RMS ripple current rating should be greater than

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 per­formance and requirements.

The LM2575 (or any of the Simple Switcher family) can be
used for both continuous and discontinuous modes of opera­tion.

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 val­ues 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 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.

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.

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-

pletely contained within the core, it generates more electro­magnetic interference (EMI). This EMI can cause problems
in sensitive circuits, or can give incorrect scope readings
because of induced voltages in the scope probe.

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 select­ing 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
sawtooth type of waveform (depending on the input voltage).
For a given input voltage and output voltage, the peak-to­peak amplitude of this inductor current waveform remains
constant. 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).

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.

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, 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 ca­pacitor and the amplitude of the inductor ripple current

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

(∆I

IND

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

cally 50 mV to 150 mV of output ripple voltage, while larger­value capacitors will reduce the ripple to approximately 20
mV to 50 mV.

Output Ripple Voltage = (∆I

) (ESR of C

IND

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.

www.national.com 18

Application Hints (Continued)

Tantalum capacitors can have a very low ESR, and should
be carefully evaluated if it is the only output capacitor. Be­cause of their good low temperature characteristics, a tan­talum 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 cur­rent.

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.

Because of their fast switching speed and low forward volt­age drop, Schottky diodes provide the best efficiency, espe­cially 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 prob­lems. 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 Schot­tky and “soft” fast-recovery diode selection guide.

OUTPUT VOLTAGE RIPPLE AND TRANSIENTS

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.

The output ripple voltage is due mainly to the inductor saw­tooth 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.

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.

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.

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 +VINwithout a resistor in series with it.
The ON /OFF pin should not be left open.

GROUNDING

To maintain output voltage stability, the power ground con­nections 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.

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.

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:

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, conser­vative design, a temperature approximately 15˚C cooler
than the maximum temperature should be selected.

4. LM2575 package thermal resistances θ

and θJC.

JA

Total power dissipated by the LM2575 can be estimated as
follows:

=(VIN)(IQ)+(VO/VIN)(I

P

D

where I

(quiescent current) and V

Q

Characteristic Curves shown previously, V
minimum input voltage, V
and I

is the load current. The dynamic losses during

LOAD

is the regulated output voltage,

O

)(V

LOAD

can be found in the

SAT

)

SAT

is the applied

IN

turn-on and turn-off are negligible if a Schottky type catch
diode is used.

When no heat sink is used, the junction temperature rise can
be determined by the following:

=(PD)(θJA)

∆T

J

To arrive at the actual operating junction temperature, add
the junction temperature rise to the maximum ambient tem­perature.

= ∆TJ+T

T

J

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.

When using a heat sink, the junction temperature rise can be
determined by the following:

=(PD)(θJC+ θ

∆T

J

interface

+ θ

Heat sink

)

The operating junction temperature will be:

J=TA

+ ∆T

J

T

As above, if the actual operating junction temperature is
greater than the selected safe operating junction tempera­ture, 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 prop­erties 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.

LM1575/LM2575/LM2575HV

www.national.com19

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.

LM1575/LM2575/LM2575HV

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.

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 calcu­late the heat sink thermal resistance required to maintain the
regulators junction temperature below the maximum operat­ing temperature.

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.

Because of the structural differences between the buck and
the buck-boost regulator topologies, the buck regulator de­sign 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).

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
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.

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

Where f
current operating conditions, the minimum V
the worst case. Select an inductor that is rated for the peak
current 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.

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.

= 52 kHz. Under normal continuous inductor

osc

represents

IN

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.

www.national.com 20

01147515

Because of the boosting function of this type of regulator, the
switch current is relatively high, especially at low input volt­ages. 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.

Additional Applications (Continued)

LM1575/LM2575/LM2575HV

Typical Load Current

200 mA for V

500 mA for V

Note: Pin numbers are for TO-220 package.

= −5.2V

IN

= −7V

IN

01147516

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 und­ervoltage 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 predeter­mined level.

≈ VZ1+2VBE(Q1)

V

TH

DELAYED STARTUP

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 approxi­mately 10 ms of delay time before the circuit begins switch­ing. 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: Complete circuit not shown.

01147517

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

FIGURE 12. Undervoltage Lockout for Buck Circuit

01147518

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.

Note: Complete circuit not shown.

01147519

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

FIGURE 14. Delayed Startup

www.national.com21

Additional Applications (Continued)

LM1575/LM2575/LM2575HV

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

A switching regulator topology in which a higher voltage is
converted to a lower voltage. Also known as a step-down
switching regulator.

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.

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.

01147520

01147521

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. Higher­grade capacitors (“low-ESR”, “high-frequency”, or “low­inductance”’) in the 100 µF–1000 µF range generally have
ESR of less than 0.15Ω.

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 volt­age. It is usually dominated by the output capacitor’s ESR
multiplied by the inductor’s ripple current (∆I

). The peak-

IND

to-peak value of this sawtooth ripple current can be deter­mined by reading the Inductor Ripple Current section of the
Application hints.

CAPACITOR RIPPLE CURRENT

RMS value of the maximum allowable alternating current at
which a capacitor can be operated continuously at a speci­fied temperature.

CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)

The purely resistive component of a real capacitor’s imped­ance (see Figure 16). It causes power loss resulting in
capacitor heating, which directly affects the capacitor’s op­erating lifetime. When used as a switching regulator output
filter, higher ESR values result in higher output ripple volt­ages.

www.national.com 22

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
turning the output switch OFF).

INDUCTOR RIPPLE CURRENT (∆I

IND

)

The peak-to-peak value of the inductor current waveform,
typically a sawtooth waveform when the regulator is operat­ing in the continuous mode (vs. discontinuous mode).

Definition of Terms (Continued)

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.

INDUCTOR SATURATION

The condition which exists when an inductor cannot hold any
more magnetic flux. When an inductor saturates, the induc­tor appears less inductive and the resistive component domi-

nates. Inductor current is then limited only by the DC resis­tance of the wire and the available source current.

OPERATING VOLT MICROSECOND CONSTANT (E

The product (in VoIt
and the time the voltage is applied. This E
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.

µs) of the voltage applied to the inductor

•

Topconstant is a

•

Top)

•

LM1575/LM2575/LM2575HV

www.national.com23

Physical Dimensions inches (millimeters)

unless otherwise noted

LM1575/LM2575/LM2575HV

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

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

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

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

www.national.com 24

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

LM1575/LM2575/LM2575HV

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.com25

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

LM1575/LM2575/LM2575HV

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 26

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

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

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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COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or
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accordance with instructions for use provided in the

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.

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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.

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