LM2576-5.0 - Micrel Semiconductor, Inc.

December 2002 1 LM2576

LM2576 Micrel

LM2576

52kHz Simple 3A Buck Regulator

Final Information

General Description

The LM2576 series of monolithic integrated circuits provide

all the active functions for a step-down (buck) switching

regulator. Fixed versions are available with a 3.3V, 5V, or 12V

fixed output. Adjustable versions have an output voltage

range from 1.23V to 37V. Both versions are capable of driving

a 3A load with excellent line and load regulation.

These regulators are simple to use because they require a

minimum number of external components and include internal

frequency compensation and a fixed-frequency oscillator.

The LM2576 series offers a high efficiency replacement for

popular three-terminal adjustable 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 available from several different

manufacturers are ideal for use with the LM2576 series. This

feature greatly simplifies the design of switch-mode power

supplies.

The feedback voltage is guaranteed to ±2% tolerance for

adjustable versions, and the output voltage is guaranteed to

±3% for fixed versions, within specified input voltages and

output load conditions. The oscillator frequency is guaranteed

to ±10%. External shutdown is included, featuring less than

200µA standby current. The output switch includes cycle-by-

cycle current limiting and thermal shutdown for full protection

under fault conditions.

870 20

Typical Applications

Features

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

• Voltage over specified line and load conditions:

Fixed version: ±3% max. output voltage

Adjustable version: ±2% max. feedback voltage

• Guaranteed 3A output current

• Wide input voltage range:

4V to 40V

• Wide output voltage range

1.23V to 37V

• Requires only 4 external components

• 52kHz fixed frequency internal oscillator

• Low power standby mode IQ typically < 200µA

• 80% efficiency (adjustable version typically > 80%)

• Uses readily available standard inductors

• Thermal shutdown and current limit protection

• 100% electrical thermal limit burn-in

Applications

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

• Efficient pre-regulator for linear regulators

• On-card switching regulators

• Positive to negative converter (inverting Buck-Boost)

• Isolated Flyback Converter using minimum number of

external components

• Negative Boost Converter

7V–40V

Unregulated

DC Input LM2576

100µF

Gnd 5

On/Off

Output

4Feedback

100µH +

1N5822 C

OUT

1000µF

R2 3.09k

R1 1k

OUT

= 1.23 1 +

( )

+5V, 3A

Regulated

Output

Note: Pin numbers are for TO-220 Package

7V–40V

Unregulated

DC Input LM2576-5.0

100µF

Gnd 5

On/Off

Output

4Feedback

100µH +

1N5822 C

OUT

1000µF

+5V, 3A

Regulated

Output

Note: Pin numbers are for TO-220 Package

Fixed Regulator in Typical Application Adjustable Regulator in Fixed Output Application

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com

LM2576 2 December 2002

LM2576 Micrel

Part Number‡Temperature Range Package

LM2576BT*†–40°C to +85°C TO-220-5

LM2576-3.3BT†–40°C to +85°C TO-220-5

LM2576-5.0BT†–40°C to +85°C TO-220-5

LM2576-12BT†–40°C to +85°C TO-220-5

LM2576BU* –40°C to +85°C TO-263-5

LM2576-3.3BU –40°C to +85°C TO-263-5

LM2576-5.0BU –40°C to +85°C TO-263-5

LM2576-12BU –40°C to +85°C TO-263-5

* Adjustable output regulators.

† Contact factory for bent or staggered leads option.

Pin Configurations

GND 5- ON/OFF

4- FEEDBACK

3- GROUND

2- OUTPUT

1- VIN

5-LEAD TO-263 (U)

GND 5- ON/OFF

4- FEEDBACK

3- GROUND

2- OUTPUT

1- VIN

5-LEAD TO-220 (T)

Ordering Information

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Electrical Characteristics Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply

over full Operating Temperature Range. Unless otherwise specified, VIN = 12V, and ILOAD = 500mA.

LM2576

Symbol Parameter Conditions Typ Limit Units

(Note 2) (Limits)

SYSTEM PARAMETERS, ADJUSTABLE REGULATORS (Note 3) Test Circuit

Figure 1

VOUT Feedback Voltage VIN = 12V , ILOAD = 0.5A 1.230 V

VOUT = 5V 1.217 V(min)

1.243 V(max)

VOUT Feedback Voltage 0.5A ≤ ILOAD ≤ 3A, 8V ≤ VIN ≤ 40V 1.230 V

LM2576 VOUT = 5V 1.193/1.180 V(min)

1.267/1.280 V(max)

ηEfficiency VIN = 12V, ILOAD = 3A, VOUT = 5V 82 %

SYSTEM PARAMETERS, 3.3V REGULATORS (Note 3) Test Circuit

Figure 1

VOUT Output Voltage VIN = 12V , ILOAD = 0.5A 3.3 V

VOUT = 3.3V 3.234 V(min)

3.366 V(max)

VOUT Output Voltage 0.5A ≤ ILOAD ≤ 3A, 6V ≤ VIN ≤ 40V 3.3 V

LM2576-3.3 VOUT = 3.3V 3.168/3.135 V(min)

3.432/3.465 V(max)

ηEfficiency VIN = 12V, ILOAD = 3A 75 %

SYSTEM PARAMETERS, 5V REGULATORS (Note 3) Test Circuit

Figure 1

VOUT Output Voltage VIN = 12V , ILOAD = 0.5A 5.0 V

VOUT = 5V 4.900 V(min)

5.100 V(max)

VOUT Output Voltage 0.5A ≤ ILOAD ≤ 3A, 8V ≤ VIN ≤ 40V 5.0 V

LM2576-5.0 VOUT = 5V 4.800/4.750 V(min)

5.200/5.250 V(max)

ηEfficiency VIN = 12V, ILOAD = 3A 82 %

SYSTEM PARAMETERS, 12V REGULATORS (Note 3) Test Circuit

Figure 1

VOUT Output Voltage VIN = 25V , ILOAD = 0.5A 12 V

VOUT = 12V 11.760 V(min)

12.240 V(max)

VOUT Output Voltage 0.5A ≤ ILOAD ≤ 3A, 15V ≤ VIN ≤ 40V 12 V

LMLM2576-12 VOUT = 12V 11.520/11.400 V(min)

12.480/12.600 V(max)

ηEfficiency VIN = 25V, ILOAD = 3A 88 %

Operating Ratings

Temperature Range –40°C ≤ TJ ≤ +125°C

Supply Voltage 40V

Absolute Maximum Ratings (Note 1)

Maximum Supply Voltage 45V

ON/OFF Pin Input Voltage –0.3V ≤ V ≤ +40V

Output Voltage to Ground (Steady State) –1V

Power Dissipation Internally Limited

Storage Temperature Range –65°C to +150°C

Minimum ESD Rating

C = 100pF, R = 1.5kΩ2 kV

FB Pin 1 kV

Lead Temperature (soldering, 10 sec.) 260°C

Maximum Junction Temperature 150°C

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LM2576 Micrel

Electrical Characteristics (continued)

LM2576 Units

Symbol Parameter Conditions Typ Limit (Limits)

(Note 2)

DEVICE PARAMETERS, ADJUSTABLE REGULATOR

IBFeedback Bias Current VOUT = 5V 50 100/500 nA

DEVICE PARAMETERS, FIXED and ADJUSTABLE REGULATORS

fOOscillator Frequency 52 kHz

47/42 kHz (min)

58/63 kHz (max)

VSAT Saturation Voltage IOUT = 3A (Note 4) 1.4 V

1.8/2.0 V(max)

DC Max Duty Cycle (ON) (Note 5) 98 %

93 %(min)

ICL Current Limit Peak Current, tON ≤ 3µs (Note 4) 5.8 A

4.2/3.5 A(min)

6.9/7.5 A(max)

ILOutput Leakage Current VIN = 40V, (Note 6), Output = 0V 2 mA(max)

Output = –1V 7.5 mA

(Note 6) Output = –1V 30 mA(max)

IQQuiescent Current (Note 6) 5 mA

10 mA(max)

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

Current 200 µA(max)

θJA Thermal Resistance T,U Package, Junction to Ambient (Note 7) 65 °C/W

θJA T,U Package, Junction to Ambient (Note 8) 45

θJC T,U Package, Junction to Case 2

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LM2576 Micrel

Electrical Characteristics (continued)

LM2576 Units

Symbol Parameter Conditions Typ Limit (Limits)

(Note 2)

ON/OFF CONTROL, FIXED and ADJUSTABLE REGULATORS Test Circuit

Figure 1

VIH ON/OFF Pin Logic VOUT = 0V 1.4 2.2/2.4 V(min)

VIL Input Level VOUT = 5V 1.2 1.0/0.8 V(max)

IIH ON /OFF Pin Logic ON /OFF Pin = 5V (OFF) 4 µA

Current 30 µA(max)

IIL ON/OFF Pin = 0V (ON) 0.01 µA

10 µA(max)

Note 1: Absolute Maximum Rating 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 room temperature limits are

100% production tested. All limits at temperature extreme are guaranteed via testing.

Note 3: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the

LM2576/LM1576 is used as shown in

Figure 1

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

Characteristics.

Note 4: Output (pin 2) sourcing current. No diode, inductor or capacitor connected to output.

Note 5: Feedback (pin 4) removed from output and connected to 0V.

Note 6: Feedback (pin 4) removed from output and connected to 12V to force the output transistor OFF.

Note 7: Junction to ambient thermal resistance (no external heat sink) for the 5-lead TO-220 package mounted vertically, with 1/2" leads in a socket, or

on PC board with minimum copper area.

Note 8: Junction to ambient thermal resistance (no external heat sink) for the 5-lead TO-220 package mounted vertically, with 1/4" leads soldered to PC

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

Note 9: Junction to ambient thermal resistance with approximately 1 square inch of pc board copper surrounding the leads. Additional copper will lower

thermal resistance further.

Typical Performance Characteristics

Normalized

Feedback Voltage*

JUNCTION TEMPERATURE (˚C)

NORMALIZED FEEDBACK VOLTAGE (mV)

-5

-10

-15

-20

-25

-75 -50 -25 0 25 50 75 100125150

VIN = 12V

ILOAD = 200mA

Normalized to TJ = 25˚C

Feedback Voltage

vs Duty Cycle*

DUTY CYCLE (%)

FEEDBACK VOLTAGE CHANGE (mV)

-5

-10

-15

-20

ILOAD = 200 mA

VIN = 40V

VIN = 7V

020 40 60 80 100

* Adjustable version only

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LM2576 Micrel

Typical Performance Characteristics (continued) (Circuit of

Figure 1

)

Supply Current

INPUT VOLTAGE (V)

SUPPLY CURRENT (mA)

20 Measured at

Ground Pin

TJ = 25˚C

VOUT = 5V

40102030405060

ILOAD to 1A

Supply Current

vs. Duty Cycle

DUTY CYCLE (%)

20.0

17.5

15.0

12.5

10.0

7.5

5.0

2.5

00 2040 6080100

VIN from 7V to 40V

ILOAD = 200 mA

SUPPLY CURRENT (mA)

JUNCTION TEMPERATURE (˚C)

200

150

100

-75

VIN = 12V

STANDBY QUIESCENT CURRENT (µA)

Standby

Quiescent Current

VIN = 40V

-50 -25 0 25 50 75 100 125150

Minimum Operating

Voltage

JUNCTION TEMPERATURE (˚C)

5.0

ILOAD = 200 mA

INPUT VOLTAGE (V)

Line Regulation

INPUT VOLTAGE (V)

NORMALIZED FEEDBACK VOLTAGE (mV)

JUNCTION TEMPERATURE (˚C)

100

-100

-75

STANDBY QUIESCENT CURRENT (µA)

Feedback Pin Current

-50 -25 0 25 50 75 100 125150

VOUT = 1.23V

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

-75 -50 -25 0 25 50 75 100125150

-2

-4

-6 51015202530

-25

-50

-75

JUNCTION TEMPERATURE (˚C)

-8

-75

NORMALIZED FREQUENCY (%)

Oscillator Frequency

-50 -25 0 25 50 75 100125150

-2

-4

--6 VIN = 12V

VIN = 40V

Normalized at 25˚C

Normalized to VIN = 10V

VOUT = 5V

ILOAD = 500mA

TJ = 25

VON/OFF = 5V

Normalized

Output Voltage

JUNCTION TEMPERATURE (˚C)

OUTPUT VOLTAGE CHANGE (mV)

100

-25

-50

-75

-100

-75 -50 -25 0 25 50 75 100125150

VIN = 12V

ILOAD = 200mA

Normalized to TJ = 25˚C

Current Limit

JUNCTION TEMPERATURE (˚C)

6.5

6.0

5.5

5.0

4.5

4.0

-75

VIN = 12V

OUTPUT CURRENT (A)

Switch

Saturation Voltage

SWITCH CURRENT (A)

1.5

-55˚C

1.4

1.2

1.0

0.8

0.6

0.4

0.2

SATURATION VOLTAGE (V)

INPUT VOLTAGE (V)

100

EFFICIENCY (%)

Efficiency

VOUT = 12V

-50 -25 0 25 50 75 100125150 0.5 1.0 1.5 2.0 2.5 3.0

25˚C

150˚C

200 mA

VOUT = 3V

0 5 10 15 20 25 30 35 40

Dropout Voltage

JUNCTION TEMPERATURE (˚C)

INPUT-OUTPUT DIFFERENTIAL (V)

2.0

-75 -50 -25 0 25 50 75 100125150

ILOAD = 3A L1 = 330 µH

ILOAD = 1A

ILOAD = 200 mA

1.5

1.0

0.5

December 2002 7 LM2576

LM2576 Micrel

100 µS/div.

Load Transient Response

+100mV

-100mV

Output

Voltage

Change

Output

Current

50V

5 µS/div.

Switching Waveforms

A: Output pin voltage 50V/div

B: Output pin current 2A/div

C: Inductor current 2A/div

D: Output ripple voltage 50 mV/div., AC coupled

Horizontal Time Base: 5µS/div

VOUT = 5V VIN = 45V

Typical Performance Characteristics (Circuit of

Figure 1

)

LM2576 8 December 2002

LM2576 Micrel

LM2575

+100 µF

+VIN

3GND 5ON/OFF 2

OUTPUT

4FEEDBACK

330 µH +

MBR360

COUT

470µF R2

VOUT

5.00V

7V - 40V

UNREGULATED

DC INPUT CIN

CIN — 100µF, 75V Aluminum Electrolytic

COUT — 470µF, 15V Aluminum Electrolytic

D1 — Schottky, MBR360

L1 — 330µH, 415-0926 (AIE)

R1 — 1k, 0.01%

R2 — 3.065k, 0.01%

5-pin TO-220 socket—2936 (Loranger Mfg. Co.)

4-pin TO-3 socket—8112-AG7 (Augat Inc.)

LM2575-5.0

+100 µF

+VIN

3GND 5ON/OFF 2

OUTPUT

4FEEDBACK

330 µH +

11DQ06

COUT

220µF

VOUT

5.00V

Note: Pin numbers are for TO-220 Package

7V - 40V

UNREGULATED

DC INPUT CIN

CIN — 100µF, 75V Aluminum Electrolytic

COUT — 330µF, 15V Aluminum Electrolytic

D1 — Schottky, 11DQ06

L1 — 100µH, 415-0926 (AIE)

5-pin TO-220 socket—2936 (Loranger Mfg. Co.)

4-pin TO-3 socket—8112-AG7 (Augat Inc.)

ON/OFF

COMPARATOR

FIXED GAIN

ERROR AMP

3 AMP

SWITCH

OUTPUT

DRIVER

VIN

FEED-

BACK

1.23V

BAND-GAP

REFERENCE 52 kHz

OSCILLATOR RESET THERMAL

SHUTDOWN CURRENT

LIMIT

Note: Pin numbers are for the TO-220 package

INTERNAL

REGULATOR ON/OFF

GND

ON/OFF

COMPARATOR

FIXED GAIN

ERROR AMP

3 AMP

SWITCH

OUTPUT

DRIVER

VIN

FEED-

BACK

1.23V

BAND-GAP

REFERENCE 52 kHz

OSCILLATOR RESET THERMAL

SHUTDOWN CURRENT

LIMIT

INTERNAL

REGULATOR ON/OFF

GND

3.1k

1.0k

Block Diagrams

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 stray 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 construction should be used for best results.

Fixed Regulator Adjustable Regulator

Test Circuits and Layout Guidelines

Figure 1.

December 2002 9 LM2576

LM2576 Micrel

Package Information

0.018 ±0.008

(0.46 ±0.20)

0.268 REF

(6.81 REF)

0.032 ±0.005

(0.81 ±0.13)

0.550 ±0.010

(13.97 ±0.25)

7°

Typ.

SEATING

PLANE

0.578 ±0.018

(14.68 ±0.46)

0.108 ±0.005

(2.74 ±0.13)

0.050 ±0.005

(1.27 ±0.13)

0.150 D ±0.005

(3.81 D ±0.13)

0.400 ±0.015

(10.16 ±0.38)

0.177 ±0.008

(4.50 ±0.20)

0.103 ±0.013

(2.62±0.33)

0.241 ±0.017

(6.12 ±0.43)

0.067 ±0.005

(1.70 ±0.127)

inch

(mm)

Dimensions:

5-Lead TO-220 (T)

0.067±0.005 0.032 ±0.003

0.360±0.005

0.600±0.025

0.405±0.005

0.060±0.005

0.176±0.005

8° MAX 0.100±0.01

0.050±0.005

0.015 ±0.002

0.004+0.004

–0.008

SEATING PLANE

0.065±0.010

20°±2°

DIM. = INCH

5-Lead TO-263 (U)

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MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA

TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com

This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or

other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel, Inc.