Datasheet LM2576BT, LM2576-5.0BU, LM2576-5.0BT, LM2576-3.3BU, LM2576-12BU Datasheet (MICREL)

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Page 1

LM2576 Micrel

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

100µF

Note: Pin numbers are for TO-220 Package

LM2576-5.0

Gnd5On/Off

Fixed Regulator in Typical Application Adjustable Regulator in Fixed Output Application

Output 2

Feedback

100µH

D1 1N5822

+5V, 3A

Regulated

Output

OUT

1000µF

7V–40V

Unregulated

DC Input

100µF

Note: Pin numbers are for TO-220 Package

OUT

= 1.23 1 +

Gnd5On/Off

( )

LM2576

R2 R1

Output 2

Feedback

100µH

D1 1N5822

OUT

1000µF

Regulated

870 20

+5V, 3A

Output

R2 3.09k R1 1k

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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.

Pin Configurations

5-LEAD TO-220 (T)

GND

5- ON/OFF 4- FEEDBACK

3- GROUND 2- OUTPUT

1- V

5-LEAD TO-263 (U)

GND

5- ON/OFF 4- FEEDBACK

3- GROUND 2- OUTPUT

1- V

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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

= 25°C, and those with boldface type apply

= 500mA.

LOAD

LM2576

Symbol Parameter Conditions Typ Limit Units

(Note 2) (Limits)

SYSTEM PARAMETERS, ADJUSTABLE REGULATORS (Note 3) Test Circuit

OUT

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

OUT

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

OUT

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

OUT

η Efficiency VIN = 25V, I

Feedback Voltage VIN = 12V , I

= 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

= 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

= 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

= 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)

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LM2576 Micrel

Electrical Characteristics (continued)

LM2576 Units

Symbol Parameter Conditions Typ Limit (Limits)

(Note 2)

DEVICE PARAMETERS, ADJUSTABLE REGULATOR

DEVICE PARAMETERS, FIXED and ADJUSTABLE REGULATORS

SAT

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

STBY

Feedback Bias Current V

= 5V 50 100/500 nA

OUT

Oscillator Frequency 52 kHz

47/42 kHz (min) 58/63 kHz (max)

Saturation Voltage I

= 3A (Note 4) 1.4 V

OUT

1.8/2.0 V(max)

93 %(min)

Current Limit Peak Current, t

≤ 3µs (Note 4) 5.8 A

4.2/3.5 A(min)

6.9/7.5 A(max)

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

Output = –1V 7.5 mA

(Note 6) Output = –1V 30 mA(max)

Quiescent Current (Note 6) 5 mA

10 mA(max)

Standby Quiescent ON/OFF Pin = 5V (OFF) 50 µA Current 200 µA(max)

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

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

Note 1: Absolute Maximum Rating indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device

Note 2: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face) . All room temperature limits are

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

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

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

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

ON/OFF Pin Logic V Input Level V

= 0V 1.4 2.2/2.4 V(min)

OUT

= 5V 1.2 1.0/0.8 V(max)

OUT

ON /OFF Pin Logic ON /OFF Pin = 5V (OFF) 4 µA Current 30 µA(max)

ON/OFF Pin = 0V (ON) 0.01 µA

is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.

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

LM2576/LM1576 is used as shown in Characteristics.

on PC board with minimum copper area.

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

thermal resistance further.

Figure 1

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

Figure 1

10 µA(max)

Typical Performance Characteristics

Normalized Feedback Voltage*

25 20 15 10

5 0

-5

-10

-15

-20

NORMALIZED FEEDBACK VOLTAGE (mV)

-25

-75 -50 -25 0 25 50 75 100125150

JUNCTION TEMPERATURE (˚C)

VIN = 12V

= 200mA

LOAD

Normalized to TJ = 25˚C

Feedback Voltage vs Duty Cycle*

20 15 10

5 0

-5

-10

-15

FEEDBACK VOLTAGE CHANGE (mV)

-20 0 20 40 60 80 100

* Adjustable version only

ILOAD = 200 mA

VIN = 40V

VIN = 7V

DUTY CYCLE (%)

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LM2576 Micrel

Typical Performance Characteristics (continued) (Circuit of

Supply Current

20 18

16 14 12 10

SUPPLY CURRENT (mA)

6 4

0102030405060

Measured at

Ground Pin

TJ = 25˚C

to 1A

LOAD

INPUT VOLTAGE (V)

Current Limit

6.5

6.0

5.5

5.0

OUTPUT CURRENT (A)

4.5

4.0

-75

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

JUNCTION TEMPERATURE (˚C)

= 5V

OUT

VIN = 12V

Supply Current vs. Duty Cycle

20.0

17.5

15.0

12.5

10.0 I

7.5

5.0

SUPPLY CURRENT (mA)

2.5 0

0 2040 6080100

= 200 mA

LOAD

VIN from 7V to 40V

DUTY CYCLE (%)

Switch Saturation Voltage

1.5

1.4

1.2

-55˚C

1.0

0.8

25˚C

0.6

150˚C

0.4

SATURATION VOLTAGE (V)

0.2 0

SWITCH CURRENT (A)

Figure 1

)

Standby Quiescent Current

200

150

100

STANDBY QUIESCENT CURRENT (µA)

-75

-50 -25 0 25 50 75 100 125150

Efficiency

100

95 90 85

200 mA

EFFICIENCY (%)

0 5 10 15 20 25 30 35 40

VIN = 40V

= 5V

ON/OFF

VIN = 12V

JUNCTION TEMPERATURE (˚C)

= 12V

OUT

200 mA

= 3V

OUT

INPUT VOLTAGE (V)

Minimum Operating Voltage

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

INPUT VOLTAGE (V)

1.0

0.5 0

-75 -50 -25 0 25 50 75 100125150

JUNCTION TEMPERATURE (˚C)

LOAD

OUT

Normalized Output Voltage

100

75 50 25

-25

-50

-75

OUTPUT VOLTAGE CHANGE (mV)

-100

-75 -50 -25 0 25 50 75 100125150

JUNCTION TEMPERATURE (˚C)

VIN = 12V

= 200mA

LOAD

Normalized to TJ = 25˚C

= 1.23V

= 200 mA

Line Regulation

Normalized to VIN = 10V

= 5V

OUT

= 500mA

LOAD

TJ = 25

6 4 2 0

-2

-4

NORMALIZED FEEDBACK VOLTAGE (mV)

-6 0

51015202530

INPUT VOLTAGE (V)

Oscillator Frequency

+8 +6

+4 +2

-2

-4

--6

NORMALIZED FREQUENCY (%)

-8

-75

-50 -25 0 25 50 75 100125150

JUNCTION TEMPERATURE (˚C)

Normalized at 25˚C

VIN = 40V

VIN = 12V

Feedback Pin Current

100

75 50 25

-25

-50

-75

STANDBY QUIESCENT CURRENT (µA)

-100

-75

-50 -25 0 25 50 75 100 125150

JUNCTION TEMPERATURE (˚C)

Dropout Voltage

2.0 I

= 3A

LOAD

1.5

1.0

= 200 mA

0.5

INPUT-OUTPUT DIFFERENTIAL (V)

-75 -50 -25 0 25 50 75 100125150

LOAD

JUNCTION TEMPERATURE (˚C)

L1 = 330 µH

= 1A

LOAD

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LM2576 Micrel

Typical Performance Characteristics (Circuit of

+100mV

Output

Voltage Change

Output

Current

-100mV

50V

Figure 1

Load Transient Response

Switching Waveforms

)

100 µS/div.

5 µS/div.

OUT

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

= 5V

= 45V

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LM2576 Micrel

Test Circuits and Layout Guidelines

FEEDBACK

7V - 40V

UNREGULATED

DC INPUT

100 µF

LM2575-5.0

7V - 40V

UNREGULATED

DC INPUT

Note: Pin numbers are for TO-220 Package

100 µF

LM2575

3GND 5ON/OFF

OUTPUT

FEEDBACK

OUTPUT

330 µH

D1 MBR360

330 µH

D1 11DQ06

C 470µF

C 220µF

OUT

5.00V

OUT

5.00V

L O A D

CIN — 100µF, 75V Aluminum Electrolytic C

— 470µF, 15V Aluminum Electrolytic

OUT

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.)

CIN — 100µF, 75V Aluminum Electrolytic C

— 330µF, 15V Aluminum Electrolytic

OUT

D1 — Schottky, 11DQ06

L O A D

L1 — 100µH, 415-0926 (AIE) 5-pin TO-220 socket—2936 (Loranger Mfg. Co.) 4-pin TO-3 socket—8112-AG7 (Augat Inc.)

Figure 1.

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.

Block Diagrams

FEEDBACK

BAND-GAP

REFERENCE

3.1k

1.0k

1.23V

FIXED GAIN ERROR AMP

52 kHz

OSCILLATOR

INTERNAL

REGULATOR

COMPARATOR

RESET

THERMAL

SHUTDOWN

ON/OFF

DRIVER

CURRENT

LIMIT

3 AMP SWITCH

FEEDBACK

FIXED GAIN ERROR AMP

ON/OFF

OUTPUT

1.23V

BAND-GAP

GND

REFERENCE

52 kHz

OSCILLATOR

INTERNAL

REGULATOR

COMPARATOR

RESET

THERMAL

SHUTDOWN

ON/OFF

DRIVER

CURRENT

LIMIT

3 AMP SWITCH

ON/OFF

OUTPUT

GND

Note: Pin numbers are for the TO-220 package

Fixed Regulator Adjustable Regulator

October 1998 4-127