Micrel LM2576 DATA SHEET

LM2576 Micrel

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LM2576

52kHz Simple 3A Buck Voltage Regulator

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-by­cycle current limiting and thermal shutdown for full protection
under fault conditions.

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

Typical Applications

7V–40V

Unregulated

DC Input

C

IN

100µF

Note: Pin numbers are for TO-220 Package

+V

+

1

LM2576-5.0

IN

3

Gnd5On/Off

Fixed Regulator in Typical Application Adjustable Regulator in Fixed Output Application

4

Output
2

Feedback

L1

100µH

D1
1N5822

+5V, 3A

Regulated

Output

+

C

OUT

1000µF

7V–40V

Unregulated

DC Input

C

IN

100µF

Note: Pin numbers are for TO-220 Package

V

OUT

1

+V

IN

+

= 1.23 1 +

3

Gnd5On/Off

( )

LM2576

R2
R1

4

Output
2

Feedback

L1

100µH

D1
1N5822

+

C

OUT

1000µF

Regulated

870 20

+5V, 3A

Output

R2 3.09k
R1 1k

4-120 October 1998

LM2576 Micrel

Ordering Information

Part Number

LM2576BT*
LM2576-3.3BT
LM2576-5.0BT
LM2576-12BT

‡

Temperature Range Package

†

†

†

†

–40°C to +85°C 5-lead TO-220
–40°C to +85°C 5-lead TO-220
–40°C to +85°C 5-lead TO-220

–40°C to +85°C 5-lead TO-220
LM2576BU* –40°C to +85°C 5-lead TO-263
LM2576-3.3BU –40°C to +85°C 5-lead TO-263
LM2576-5.0BU –40°C to +85°C 5-lead TO-263
LM2576-12BU –40°C to +85°C 5-lead TO-263

* Adjustable output regulators.

†

Contact factory for bent or staggered leads option.

4

Pin Configurations

5-LEAD TO-220 (T)

GND

5- ON/OFF
4- FEEDBACK

3- GROUND
2- OUTPUT

1- V

IN

5-LEAD TO-263 (U)

GND

5- ON/OFF
4- FEEDBACK

3- GROUND
2- OUTPUT

1- V

IN

October 1998 4-121

LM2576 Micrel

Absolute Maximum Ratings (Note 1)

Maximum Supply Voltage 45V
ON/OFF Pin Input Voltage –0.3V ≤ V ≤ +40V

Operating Ratings

Temperature Range –40°C ≤ TJ ≤ +125°C

Supply Voltage 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 = 1.5kΩ 2 kV

FB Pin 1 kV
Lead Temperature (soldering, 10 sec.) 260°C
Maximum Junction Temperature 150°C

Electrical Characteristics Specifications with standard typeface are for T

over full Operating Temperature Range. Unless otherwise specified, V

= 12V, and I

IN

= 25°C, and those with boldface type apply

J

= 500mA.

LOAD

LM2576

Symbol Parameter Conditions Typ Limit Units

(Note 2) (Limits)

SYSTEM PARAMETERS, ADJUSTABLE REGULATORS (Note 3) Test Circuit

V

OUT

V

OUT

η Efficiency VIN = 12V, I
SYSTEM PARAMETERS, 3.3V REGULATORS (Note 3) Test Circuit
V

OUT

V

OUT

η Efficiency VIN = 12V, I
SYSTEM PARAMETERS, 5V REGULATORS (Note 3) Test Circuit
V

OUT

V

OUT

η Efficiency VIN = 12V, I
SYSTEM PARAMETERS, 12V REGULATORS (Note 3) Test Circuit
V

OUT

V

OUT

η Efficiency VIN = 25V, I

Feedback Voltage VIN = 12V , I

V

= 5V 1.217 V(min)

OUT

Feedback Voltage 0.5A ≤ I
LM2576 V

LOAD

= 5V 1.193/1.180 V(min)

OUT

Output Voltage VIN = 12V , I

V

= 3.3V 3.234 V(min)

OUT

Output Voltage 0.5A ≤ I
LM2576-3.3 V

LOAD

= 3.3V 3.168/3.135 V(min)

OUT

Output Voltage VIN = 12V , I

V

= 5V 4.900 V(min)

OUT

Output Voltage 0.5A ≤ I
LM2576-5.0 V

LOAD

= 5V 4.800/4.750 V(min)

OUT

Output Voltage VIN = 25V , I

V

= 12V 11.760 V(min)

OUT

Output Voltage 0.5A ≤ I
LMLM2576-12 V

LOAD

= 12V 11.520/11.400 V(min)

OUT

= 0.5A 1.230 V

LOAD

≤ 3A, 6V ≤ VIN ≤ 40V 1.230 V

LOAD

= 3A, V

= 5V 82 %

OUT

Figure 1

= 0.5A 3.3 V

LOAD

≤ 3A, 6V ≤ VIN ≤ 40V 3.3 V

= 3A 75 %

LOAD

Figure 1

= 0.5A 5.0 V

LOAD

≤ 3A, 8V ≤ VIN ≤ 40V 5.0 V

= 3A 82 %

LOAD

Figure 1

= 0.5A 12 V

LOAD

≤ 3A, 15V ≤ VIN ≤ 40V 12 V

= 3A 88 %

LOAD

Figure 1

1.243 V(max)

1.267/1.280 V(max)

3.366 V(max)

3.432/3.465 V(max)

5.100 V(max)

5.200/5.250 V(max)

12.240 V(max)

12.480/12.600 V(max)

4-122 October 1998