LM2575HVEP - National Semiconductor

LM2575EP/LM2575HVEP

SIMPLE SWITCHER®1A Step-Down Voltage Regulator

General Description

The LM2575EP series of regulators are monolithic inte-

grated 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 de-

vices 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 LM2575EP 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

LM2575EP are available from several different manufactur-

ers. This feature greatly simplifies the design of switch-mode

power supplies.

Other features include a guaranteed ±4% tolerance on out-

put voltage within specified input voltages and output load

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

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

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

ing, as well as thermal shutdown for full protection under

fault conditions.

ENHANCED PLASTIC

•Extended Temperature Performance of

−40˚C ≤T

≤+125˚C

•Baseline Control - Single Fab & Assembly Site

•Process Change Notification (PCN)

•Qualification & Reliability Data

•Solder (PbSn) Lead Finish is standard

•Enhanced Diminishing Manufacturing Sources (DMS)

Support

Features

n3.3V, 5V, 12V, 15V, and adjustable output versions

nAdjustable version output voltage range,

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

line and load conditions

nGuaranteed 1A output current

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

nRequires only 4 external components

n52 kHz fixed frequency internal oscillator

nTTL shutdown capability, low power standby mode

nHigh efficiency

nUses readily available standard inductors

nThermal shutdown and current limit protection

Product Enhancement tested

Applications

nSimple high-efficiency step-down (buck) regulator

nEfficient pre-regulator for linear regulators

nOn-card switching regulators

nPositive to negative converter (Buck-Boost)

nSelected Military Applications

nSelected Avionics Applications

Ordering Information

PART NUMBER VID PART NUMBER NS PACKAGE NUMBER (Note 3)

LM2575HVS-5.0EP V62/04742-01 TS5B

LM2575HVS-ADJEP V62/04742-02 TS5B

(Notes 1, 2) TBD TBD

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

December 2004

LM2575EP/LM2575HVEP Series SIMPLE SWITCHER 1A Step-Down Voltage Regulator

Ordering Information (Continued)

Note 1: For the following (Enhanced Plastic) version, check for availability: LM2575M-12EP, LM2575M-15EP, LM2575M-3.3EP, LM2575M-5.0EP, LM2575M-

ADJEP, LM2575MX-12EP, LM2575MX-15EP, LM2575MX-3.3EP, LM2575MX-5.0EP, LM2575MX-ADJEP, LM2575N-12EP, LM2575N-15EP, LM2575N-5.0EP,

LM2575N-ADJEP, LM2575T-12EP, LM2575T-15EP, LM2575T-3.3EP, LM2575T-5.0EP, LM2575T-ADJEP, LM2575S-12EP, LM2575S-15EP, LM2575S-3.3EP,

LM2575S-5.0EP, LM2575S-ADJEP, LM2575SX-12EP, LM2575SX-15EP, LM2575SX-3.3EP, LM2575SX-5.0EP, LM2575SX-ADJEP, LM2575HVM-12EP,

LM2575HVM-15EP, LM2575HVM-5.0EP, LM2575HVM-ADJEP, LM2575HVMX-12EP, LM2575HVMX-15EP, LM2575HVMX-5.0EP, LM2575HVMX-ADJEP,

LM2575HVN-12EP, LM2575HVN-15EP, LM2575HVN-5.0EP, LM2575HVN-ADJEP, LM2575HVT-12EP, LM2575HVT-15EP, LM2575HVT-3.3EP, LM2575HVT-

5.0EP, LM2575HVT-ADJEP, LM2575HVS-12EP, LM2575HVS-15EP, LM2575HVS-3.3EP, LM2575HVSX-12EP, LM2575HVSX-15EP, LM2575HVSX-3.3EP,

LM2575HVSX-5.0EP, LM2575HVSX-ADJEP. Parts listed with an "X" are provided in Tape & Reel and parts without an "X" are in Rails.

Note 2: FOR ADDITIONAL ORDERING AND PRODUCT INFORMATION, PLEASE VISIT THE ENHANCED PLASTIC WEB SITE AT: www.national.com/mil

Note 3: Refer to package details under Physical Dimensions

Typical Application (Fixed Output Voltage

Versions)

20113201

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

Block Diagram and Typical Application

20113202

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.

LM2575EP/LM2575HVEP

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Connection Diagrams (XX indicates output voltage option. See Device Reference Information table for com-

plete part number.)

Straight Leads

5–Lead TO-22 (T)

Bent, Staggered Leads

5-Lead TO-220 (T)

20113222

Top View

See NS Package Number T05A

20113223

Top View

20113224

Side View

See NS Package Number T05D

16–Lead DIP (N) 24-Lead Surface Mount (M)

20113225

*No Internal Connection

Top ViewSee NS Package Number N16A 20113226

*No Internal Connection

Top View

See NS Package Number M24B

TO-263(S)

5-Lead Surface-Mount Package

20113229

Top View

20113230

Side View

See NS Package Number TS5B

LM2575EP/LM2575HVEP

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Device Reference Information

Package NSC Standard High Temperature

Type Package Voltage Rating Voltage Rating Range

Number (40V) (60V)

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

Straight Leads LM2575T-5.0EP LM2575HVT-5.0EP

LM2575T-12EP LM2575HVT-12EP

LM2575T-15EP LM2575HVT-15EP

LM2575T-ADJEP LM2575HVT-ADJEP

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

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

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

LM2575T-15EP Flow LB03 LM2575HVT-15EP Flow LB03

LM2575T-ADJEP Flow

LB03

LM2575HVT-ADJEP Flow LB03

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

≤+125˚C

DIP LM2575N-12EP LM2575HVN-12EP

LM2575N-15EP LM2575HVN-15EP

LM2575N-ADJEP LM2575HVN-ADJEP

24-Pin M24B LM2575M-5.0EP LM2575HVM-5.0EP

Surface Mount LM2575M-12EP LM2575HVM-12EP

LM2575M-15EP LM2575HVM-15EP

LM2575M-ADJEP LM2575HVM-ADJEP

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

Surface Mount LM2575S-5.0EP LM2575HVS-5.0EP

LM2575S-12EP LM2575HVS-12EP

LM2575S-15EP LM2575HVS-15EP

LM2575S-ADJEP LM2575HVS-ADJEP

LM2575EP/LM2575HVEP

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Absolute Maximum Ratings (Note 4)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Maximum Supply Voltage

LM2575EP 45V

LM2575HVEP 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

Minimum ESD Rating

(C = 100 pF, R = 1.5 kΩ)2kV

Lead Temperature

(Soldering, 10 sec.) 260˚C

Operating Ratings

Temperature Range

LM2575EP/LM2575HVEP −40˚C ≤T

≤+125˚C

Supply Voltage

LM2575EP 40V

LM2575HVEP 60V

LM2575-3.3EP, LM2575HV-3.3EP

Electrical Characteristics (Note 16)

Specifications with standard type face are for T

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

ture Range .

Symbol Parameter Conditions Typ LM2575-3.3EP Units

(Limits)

LM2575HV-3.3EP

Limit

(Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit Figure 2

OUT

Output Voltage V

= 12V, I

LOAD

= 0.2A 3.3 V

Circuit of Figure 2 3.234 V(Min)

3.366 V(Max)

OUT

Output Voltage 4.75V ≤V

≤40V, 0.2A ≤I

LOAD

≤1A 3.3 V

LM2575EP Circuit of Figure 2 3.168/3.135 V(Min)

3.432/3.465 V(Max)

OUT

Output Voltage 4.75V ≤V

≤60V, 0.2A ≤I

LOAD

≤1A 3.3 V

LM2575HVEP Circuit of Figure 2 3.168/3.135 V(Min)

3.450/3.482 V(Max)

ηEfficiency V

= 12V, I

LOAD

=1A 75 %

LM2575-5.0EP, LM2575HV-5.0EP

Electrical Characteristics (Note 16)

Specifications with standard type face are for T

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

ture Range.

Symbol Parameter Conditions Typ LM2575-5.0EP Units

(Limits)

LM2575HV-5.0EP

Limit

(Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit Figure 2

OUT

Output Voltage V

= 12V, I

LOAD

= 0.2A 5.0 V

Circuit of Figure 2 4.900 V(Min)

5.100 V(Max)

OUT

Output Voltage 0.2A ≤I

LOAD

≤1A, 5.0 V

LM2575EP 8V ≤V

≤40V 4.800/4.750 V(Min)

Circuit of Figure 2 5.200/5.250 V(Max)

OUT

Output Voltage 0.2A ≤I

LOAD

≤1A, 5.0 V

LM2575HVEP 8V ≤V

≤60V 4.800/4.750 V(Min)

Circuit of Figure 2 5.225/5.275 V(Max)

LM2575EP/LM2575HVEP

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LM2575-5.0EP, LM2575HV-5.0EP

Electrical Characteristics (Note 16) (Continued)

Specifications with standard type face are for T

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

ture Range.

Symbol Parameter Conditions Typ LM2575-5.0EP Units

(Limits)

LM2575HV-5.0EP

Limit

(Note 5)

ηEfficiency V

= 12V, I

LOAD

=1A 77 %

LM2575-12EP, LM2575HV-12EP

Electrical Characteristics (Note 16)

Specifications with standard type face are for T

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

ture Range .

Symbol Parameter Conditions Typ LM2575-12EP Units

(Limits)

LM2575HV-12EP

Limit

(Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit Figure 2

OUT

Output Voltage V

= 25V, I

LOAD

= 0.2A 12 V

Circuit of Figure 2 11.76 V(Min)

12.24 V(Max)

OUT

Output Voltage 0.2A ≤I

LOAD

≤1A, 12 V

LM2575EP 15V ≤V

≤40V 11.52/11.40 V(Min)

Circuit of Figure 2 12.48/12.60 V(Max)

OUT

Output Voltage 0.2A ≤I

LOAD

≤1A, 12 V

LM2575HVEP 15V ≤V

≤60V 11.52/11.40 V(Min)

Circuit of Figure 2 12.54/12.66 V(Max)

ηEfficiency V

= 15V, I

LOAD

=1A 88 %

LM2575-15EP, LM2575HV-15EP

Electrical Characteristics (Note 16)

Specifications with standard type face are for T

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

ture Range .

Symbol Parameter Conditions Typ LM2575-15EP Units

(Limits)

LM2575HV-15EP

Limit

(Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit Figure 2

OUT

Output Voltage V

= 30V, I

LOAD

= 0.2A 15 V

Circuit of Figure 2 14.70 V(Min)

15.30 V(Max)

OUT

Output Voltage 0.2A ≤I

LOAD

≤1A, 15 V

LM2575EP 18V ≤V

≤40V 14.40/14.25 V(Min)

Circuit of Figure 2 15.60/15.75 V(Max)

OUT

Output Voltage 0.2A ≤I

LOAD

≤1A, 15 V

LM2575HVEP 18V ≤V

≤60V 14.40/14.25 V(Min)

Circuit of Figure 2 15.68/15.83 V(Max)

ηEfficiency V

= 18V, I

LOAD

=1A 88 %

LM2575EP/LM2575HVEP

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LM2575-ADJEP, LM2575HV-ADJEP

Electrical Characteristics (Note 16)

Specifications with standard type face are for T

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

Range.

Symbol Parameter Conditions Typ LM2575-ADJEP Units

(Limits)

LM2575HV-ADJEP

Limit

(Note 5)

SYSTEM PARAMETERS (Note 6) Test Circuit Figure 2

OUT

Feedback Voltage V

= 12V, I

LOAD

= 0.2A 1.230 V

OUT

= 5V 1.217 V(Min)

Circuit of Figure 2 1.243 V(Max)

OUT

Feedback Voltage 0.2A ≤I

LOAD

≤1A, 1.230 V

LM2575EP 8V ≤V

≤40V 1.193/1.180 V(Min)

OUT

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

OUT

Feedback Voltage 0.2A ≤I

LOAD

≤1A, 1.230 V

LM2575HVEP 8V ≤V

≤60V 1.193/1.180 V(Min)

OUT

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

ηEfficiency V

= 12V, I

LOAD

= 1A, V

OUT

=5V 77 %

All Output Voltage Versions

Electrical Characteristics (Note 16)

Specifications with standard type face are for T

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

ture Range. Unless otherwise specified, V

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

= 25V for the 12V version,

and V

= 30V for the 15V version. I

LOAD

= 200 mA.

Symbol Parameter Conditions Typ LM2575-XXEP Units

(Limits)

LM2575HV-XXEP

Limit

(Note 5)

DEVICE PARAMETERS

Feedback Bias Current V

OUT

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

Oscillator Frequency (Note 15) 52 kHz

47/42 kHz(Min)

58/63 kHz(Max)

SAT

Saturation Voltage I

OUT

= 1A (Note 7) 0.9 V

1.2/1.4 V(Max)

DC Max Duty Cycle (ON) (Note 8) 98 %

93 %(Min)

Current Limit Peak Current (Notes 7, 15) 2.2 A

1.7/1.3 A(Min)

3.0/3.2 A(Max)

Output Leakage (Notes 9, 10) Output = 0V 2 mA(Max)

Current Output = −1V 7.5 mA

Output = −1V 30 mA(Max)

Quiescent Current (Note 9) 5 mA

10 mA(Max)

STBY

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

Current 200 µA(Max)

LM2575EP/LM2575HVEP

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All Output Voltage Versions

Electrical Characteristics (Note 16) (Continued)

Specifications with standard type face are for T

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

ture Range. Unless otherwise specified, V

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

= 25V for the 12V version,

and V

= 30V for the 15V version. I

LOAD

= 200 mA.

Symbol Parameter Conditions Typ LM2575-XXEP Units

(Limits)

LM2575HV-XXEP

Limit

(Note 5)

DEVICE PARAMETERS

Thermal Resistance T Package, Junction to Ambient (Note 11) 65

T Package, Junction to Ambient (Note 12) 45 ˚C/W

T Package, Junction to Case 2

N Package, Junction to Ambient (Note 13) 85

M Package, Junction to Ambient (Note 13) 100

S Package, Junction to Ambient (Note 14) 37

ON /OFF CONTROL Test Circuit Figure 2

ON /OFF Pin Logic V

OUT

= 0V 1.4 2.2/2.4 V(Min)

Input Level V

OUT

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

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

Current 30 µA(Max)

ON /OFF Pin = 0V (ON) 0µA

10 µA(Max)

Note 4: 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 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%

production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods.

Note 6: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the

LM2575EP is used as shown in the Figure 2 test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.

Note 7: Output (pin 2) sourcing current. No diode, inductor or capacitor connected to output pin.

Note 8: Feedback (pin 4) removed from output and connected to 0V.

Note 9: 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 10: VIN = 40V (60V for the high voltage version).

Note 11: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with

⁄

inch leads in a socket, or on a

PC board with minimum copper area.

Note 12: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with

⁄

inch leads soldered to a PC board

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

Note 13: 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 14: 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, θJA is 50˚C/W; with 1 square inch of copper area, θJA is 37˚C/W; and with 1.6 or more square inches of copper area, θJA is 32˚C/W.

Note 15: 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 16: "Testing and other quality control techniques are used to the extent deemed necessary to ensure product performance over the specified temperature

range. Product may not necessarily be tested across the full temperature range and all parameters may not necessarily be tested. In the absence of specific

PARAMETRIC testing, product performance is assured by characterization and/or design."

LM2575EP/LM2575HVEP

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Typical Performance Characteristics (Circuit of Figure 2)

Normalized Output Voltage Line Regulation Dropout Voltage

20113232 20113233 20113234

Current Limit Quiescent Current

Standby

Quiescent Current

20113235 20113236 20113237

Oscillator Frequency

Switch Saturation

Voltage Efficiency

20113238 20113239 20113240

Minimum Operating Voltage

Quiescent Current

vs Duty Cycle

Feedback Voltage

vs Duty Cycle

20113241 20113242 20113243

LM2575EP/LM2575HVEP

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

Feedback Pin Current

Maximum Power Dissipation

(TO-263) (See (Note 14))

20113205 20113228

Switching Waveforms Load Transient Response

20113206

VOUT =5V

A: Output Pin Voltage, 10V/div

B: Output Pin Current, 1A/div

C: Inductor Current, 0.5A/div

D: Output Ripple Voltage, 20 mV/div,

AC-Coupled

Horizontal Time Base: 5 µs/div

20113207

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

Adjustable version, physically locate the programming resis-

tors near the regulator, to keep the sensitive feedback wiring

short.

LM2575EP/LM2575HVEP

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Test Circuit and Layout Guidelines (Continued)

Fixed Output Voltage Versions

20113208

CIN — 100 µF, 75V, Aluminum Electrolytic

COUT — 330 µF, 25V, Aluminum Electrolytic

D1 — Schottky, 11DQ06

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

Adjustable Output Voltage Version

20113209

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

R1 — 2k, 0.1%

R2 — 6.12k, 0.1%

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

FIGURE 2.

LM2575EP/LM2575HVEP

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LM2575EP Series Buck Regulator Design Procedure

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

Given: V

OUT

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

15V) V

(Max) = Maximum Input Voltage I

LOAD

(Max) =

Maximum Load Current

Given: V

OUT

=5VV

(Max) = 20V I

LOAD

(Max) = 0.8A

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

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

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

output voltages, see the design procedure for the adjustable

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

the inductance region intersected by V

(Max) and

LOAD

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

Identify the inductor value from the inductor code, and

select an appropriate inductor from the table shown in

Figure 9. Part numbers are listed for three inductor

manufacturers. The inductor chosen must be rated for

operation at the LM2575EP switching frequency (52 kHz)

and for a current rating of 1.15 x I

LOAD

. For additional

inductor information, see the inductor section in the

Application Hints section of this data sheet.

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

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

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

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

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

PE-52627, or RL1952.

2. Output Capacitor Selection (C

OUT

)A.The value of the

output capacitor together with the inductor defines the

dominate pole-pair of the switching regulator loop. For

stable operation and an acceptable output ripple voltage,

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

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

voltage rating should be at least 1.5 times greater than the

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

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

Higher voltage electrolytic capacitors generally have lower

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

select a capacitor rated for a higher voltage than would

normally be needed.

2. Output Capacitor Selection (C

OUT

)A.C

OUT

= 100 µF

to 470 µF standard aluminum electrolytic. B. Capacitor

voltage rating = 20V.

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

rating must be at least 1.2 times greater than the maximum

load current. Also, if the power supply design must

withstand a continuous output short, the diode should have

a current rating equal to the maximum current limit of the

LM2575EP. The most stressful condition for this diode is an

overload or shorted output condition. B. The reverse voltage

rating of the diode should be at least 1.25 times the

maximum input voltage.

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

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

Schottky diode, or any of the suggested fast-recovery

diodes shown in Figure 8.

4. Input Capacitor (C

)An aluminum or tantalum

electrolytic bypass capacitor located close to the regulator is

needed for stable operation.

4. Input Capacitor (C

)A 47 µF, 25V aluminum electrolytic

capacitor located near the input and ground pins provides

sufficient bypassing.

LM2575EP/LM2575HVEP

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Inductor Value Selection Guides (For Continuous Mode Operation)

20113210

FIGURE 3. LM2575(HV)-3.3EP

20113211

FIGURE 4. LM2575(HV)-5.0EP

20113212

FIGURE 5. LM2575(HV)-12EP

20113213

FIGURE 6. LM2575(HV)-15EP

20113214

FIGURE 7. LM2575(HV)-ADJEP

LM2575EP/LM2575HVEP

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

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

Given: V

OUT

= Regulated Output Voltage V

(Max) =

Maximum Input Voltage I

LOAD

(Max) = Maximum Load

Current F = Switching Frequency (Fixed at 52 kHz)

Given: V

OUT

= 10V V

(Max) = 25V I

LOAD

(Max) = 1A F =

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.

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

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

1.Programming Output Voltage (Selecting R1 and R2)

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:

B. Use the E •T value from the previous formula and match

it with the E •T number on the vertical axis of the Inductor

Value Selection Guide shown in Figure 7.C. On the hori-

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

inductance region intersected by the E •T value and the

maximum load current value, and note the inductor code for

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

code, and select an appropriate inductor from the table shown

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

facturers. The inductor chosen must be rated for operation at

the LM2575EP switching frequency (52 kHz) and for a current

rating of 1.15 x I

LOAD

. For additional inductor information, see

the inductor section in the application hints section of this data

sheet.

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

B. E•T = 115 V •µs C. I

LOAD

(Max) = 1A D. Inductance

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

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

Renco part #RL-1961.

3. Output Capacitor Selection (C

OUT

)A.The value of the

output capacitor together with the inductor defines the

dominate pole-pair of the switching regulator loop. For

stable operation, the capacitor must satisfy the following

requirement:

The above formula yields capacitor values between 10 µF

and 2000 µF that will satisfy the loop requirements for stable

operation. But to achieve an acceptable output ripple voltage,

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

sponse, the output capacitor may need to be several times

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

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

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

is recommended. Higher voltage electrolytic capacitors gen-

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

necessary to select a capacitor rate for a higher voltage than

would normally be needed.

3. Output Capacitor Selection (C

OUT

)A.

However, for acceptable output ripple voltage select C

OUT

≥

220 µF C

OUT

= 220 µF electrolytic capacitor

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

LM2575EP. 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.

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.

LM2575EP/LM2575HVEP

www.national.com 14

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

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

5. Input Capacitor (C

)An aluminum or tantalum

electrolytic bypass capacitor located close to the regulator is

needed for stable operation.

5. Input Capacitor (C

)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.

LM2575EP/LM2575HVEP

www.national.com15

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

Schottky Fast Recovery

1A 3A 1A 3A

20V 1N5817 1N5820

MBR120P MBR320

SR102 SR302

30V 1N5818 1N5821

MBR130P MBR330 The following

diodes are all

rated to 100V

11DF1

MUR110

HER102

The following

diodes are all

rated to 100V

31DF1

MURD310

HER302

11DQ03 31DQ03

SR103 SR303

40V 1N5819 IN5822

MBR140P MBR340

11DQ04 31DQ04

SR104 SR304

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 17) (Note 18) (Note 19)

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

Note 18: Pulse Engineering, (619) 674-8100, P.O. Box 12236, San Diego, CA 92112.

Note 19: Renco Electronics Inc., (516) 586-5566, 60 Jeffryn Blvd. East, Deer Park, NY 11729.

FIGURE 9. Inductor Selection by Manufacturer’s Part Number

LM2575EP/LM2575HVEP

www.national.com 16

Application Hints

INPUT CAPACITOR (C

)

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

passed with at least a 47 µF electrolytic capacitor. The

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

regulator.

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

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.

The LM2575EP (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 val-

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

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

the maximum DC current. With relatively heavy load cur-

rents, the circuit operates in the continuous mode (inductor

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

circuit will be forced to the discontinuous mode (inductor

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

mode of operation is perfectly acceptable. For light loads

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

operate the regulator in the discontinuous mode, primarily

because of the lower inductor values required for the discon-

tinuous mode.

The 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 electro-

magnetic interference (EMI). This EMI can cause problems

in sensitive circuits, or can give incorrect scope readings

because of induced voltages in the scope probe.

The inductors listed in the selection chart include ferrite pot

core construction for AIE, powdered iron toroid for Pulse

Engineering, and ferrite bobbin core for Renco.

An inductor should not be operated beyond its maximum

rated current because it may saturate. When an inductor

begins to saturate, the inductance decreases rapidly and the

inductor begins to look mainly resistive (the DC resistance of

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

rapidly. Different inductor types have different saturation

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

ing an inductor.

The inductor manufacturer’s data sheets include current and

energy limits to avoid inductor saturation.

INDUCTOR RIPPLE CURRENT

When the switcher is operating in the continuous mode, the

inductor current waveform ranges from a triangular to a

sawtooth type of waveform (depending on the input voltage).

For a given input voltage and output voltage, the peak-to-

peak amplitude of this inductor current waveform remains

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

tooth current waveform also rises or falls. The average DC

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

buck regulator configuration).

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 LM2575EP using short pc board traces. Standard

aluminum electrolytics are usually adequate, but low ESR

types are recommended for low output ripple voltage and

good stability. The ESR of a capacitor depends on many

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

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

low voltage (less than 12V) electrolytic capacitors usually

have higher ESR numbers.

The amount of output ripple voltage is primarily a function of

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

pacitor and the amplitude of the inductor ripple current

(∆I

IND

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

tion Hints.

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

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

value capacitors will reduce the ripple to approximately 20

mV to 50 mV.

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

0.05Ωcan cause instability in the regulator.

LM2575EP/LM2575HVEP

www.national.com17

Application Hints (Continued)

Tantalum capacitors can have a very low ESR, and should

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

cause of their good low temperature characteristics, a tan-

talum can be used in parallel with aluminum electrolytics,

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

tance.

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

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

rent.

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 LM2575EP using short leads and

short printed circuit traces.

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.

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 saw-

tooth ripple current multiplied by the ESR of the output

capacitor. (See the inductor selection in the application

hints.)

The voltage spikes are present because of the fast switching

action of the output switch, and the parasitic inductance of

the output filter capacitor. To minimize these voltage spikes,

special low inductance capacitors can be used, and their

lead lengths must be kept short. Wiring inductance, stray

capacitance, as well as the scope probe used to evaluate

these transients, all contribute to the amplitude of these

spikes.

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 LM2575EP (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 kΩbecause 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 +V

without a resistor in series with it.

The ON /OFF pin should not be left open.

GROUNDING

To maintain output voltage stability, the power ground con-

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

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

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

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

same copper lead frame.

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

LM2575EP junction temperature within the allowed operat-

ing 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 (125˚C for the

LM2575EP). For a safe, conservative design, a tem-

perature approximately 15˚C cooler than the maximum

temperature should be selected.

4. LM2575EP package thermal resistances θ

and θ

Total power dissipated by the LM2575EP can be estimated

as follows:

=(V

)(I

)+(V

)(I

LOAD

)(V

SAT

)

where I

(quiescent current) and V

SAT

can be found in the

Characteristic Curves shown previously, V

is the applied

minimum input voltage, V

is the regulated output voltage,

and I

LOAD

is the load current. The dynamic losses during

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:

∆T

=(P

)(θ

)

To arrive at the actual operating junction temperature, add

the junction temperature rise to the maximum ambient tem-

perature.

=∆T

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:

∆T

=(P

)(θ

+θ

interface

+θ

Heat sink

)

The operating junction temperature will be:

+∆T

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 LM2575EP 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.

LM2575EP/LM2575HVEP

www.national.com 18

Application Hints (Continued)

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

readily conducted through the leads to the printed circuit

board copper, which is acting as a heat sink.

For best thermal performance, the ground pins and all the

unconnected pins should be soldered to generous amounts

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

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

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

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

there is no direct copper contact between the two sides.

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

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

a carefully engineered pc board.

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.

Additional Applications

INVERTING REGULATOR

Figure 10 shows a LM2575-12EP in a buck-boost configu-

ration 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 volt-

age 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

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 de-

sign procedure section can not be used to select the inductor

or the output capacitor. The recommended range of inductor

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

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

is normally required for buck designs. Low input voltages or

high output currents require a large value output capacitor

(in the thousands of micro Farads).

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

switch current, can be calculated from the following formula:

Where f

osc

= 52 kHz. Under normal continuous inductor

current operating conditions, the minimum V

represents

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 LM2575EP is

+28V, or +48V for the LM2575HVEP.

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.

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

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.

20113215

FIGURE 10. Inverting Buck-Boost Develops −12V

LM2575EP/LM2575HVEP

www.national.com19

Additional Applications (Continued)

UNDERVOLTAGE LOCKOUT

In some applications it is desirable to keep the regulator off

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

ervoltage lockout circuit which accomplishes this task is

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

applied to a buck-boost configuration. These circuits keep

the regulator off until the input voltage reaches a predeter-

mined level.

≈V

+2V

(Q1)

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 approxi-

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

ing. Increasing the RC time constant can provide longer

delay times. But excessively large RC time constants can

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

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

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.

20113216

Typical Load Current

200 mA for VIN = −5.2V

500 mA for VIN = −7V

Note: Pin numbers are for TO-220 package.

FIGURE 11. Negative Boost

20113217

Note: Complete circuit not shown.

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

FIGURE 12. Undervoltage Lockout for Buck Circuit

20113218

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

20113219

Note: Complete circuit not shown.

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

FIGURE 14. Delayed Startup

LM2575EP/LM2575HVEP

www.national.com 20

Additional Applications (Continued)

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 LM2575EP switch is OFF.

EFFICIENCY (η)

The proportion of input power actually delivered to the load.

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

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

erating lifetime. When used as a switching regulator output

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

ages.

Most standard aluminum electrolytic capacitors in the

100 µF–1000 µF range have 0.5Ωto 0.1ΩESR. 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.

EQUIVALENT SERIES INDUCTANCE (ESL)

The pure inductance component of a capacitor (see Figure

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

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

this unwanted inductance causes voltage spikes to appear

on the output.

OUTPUT RIPPLE VOLTAGE

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

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

multiplied by the inductor’s ripple current (∆I

IND

). The peak-

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

mined by reading the Inductor Ripple Current section of the

Application hints.

CAPACITOR RIPPLE CURRENT

RMS value of the maximum allowable alternating current at

which a capacitor can be operated continuously at a speci-

fied temperature.

STANDBY QUIESCENT CURRENT (I

STBY

)

Supply current required by the LM2575EP 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 operat-

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

20113220

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

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

20113221

FIGURE 16. Simple Model of a Real Capacitor

LM2575EP/LM2575HVEP

www.national.com21

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 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.

OPERATING VOLT MICROSECOND CONSTANT (E•T

)

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

and the time the voltage is applied. This E•T

constant is a

measure of the energy handling capability of an inductor and

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

number of turns, and the duty cycle.

LM2575EP/LM2575HVEP

www.national.com 22

Physical Dimensions inches (millimeters)

unless otherwise noted

24-Lead Molded Package

NS Package Number M24B

16-Lead Molded DIP (N)

NS Package Number N16A

LM2575EP/LM2575HVEP

www.national.com23

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

5-Lead TO-220 (T)

NS Package Number T05A

LM2575EP/LM2575HVEP

www.national.com 24

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

TO-263, Molded, 5-Lead Surface Mount

NS Package Number TS5B

LM2575EP/LM2575HVEP

www.national.com25

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

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

NS Package Number T05D

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.

For the most current product information visit us at www.national.com.

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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.

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LM2575EP/LM2575HVEP Series SIMPLE SWITCHER 1A Step-Down Voltage Regulator