ON Semiconductor LM2576 Technical data

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LM2576

3.0 A, 15 V, Step−Down
Switching Regulator

The LM2576 series of regulators are monolithic integrated circuits
ideally suited for easy and convenient design of a step−down
switching regulator (buck converter). All circuits of this series are
capable of driving a 3.0 A load with excellent line and load regulation.
These devices are available in fixed output voltages of 3.3 V, 5.0 V,
12 V, 15 V, and an adjustable output version.

These regulators were designed to minimize the number of external
components to simplify the power supply design. Standard series of
inductors optimized for use with the LM2576 are offered by several
different inductor manufacturers.

Since the LM2576 converter is a switch−mode power supply, its
efficiency is significantly higher in comparison with popular
three−terminal linear regulators, especially with higher input voltages.
In many cases, the power dissipated is so low that no heatsink is
required or its size could be reduced dramatically.

A standard series of inductors optimized for use with the LM2576
are available from several different manufacturers. This feature
greatly simplifies the design of switch−mode power supplies.

The LM2576 features include a guaranteed ±4% tolerance on output
voltage within specified input voltages and output load conditions, and
±10% on the oscillator frequency (±2% over 0°C to 125°C). External
shutdown is included, featuring 80 mA (typical) standby current. The
output switch includes cycle−by−cycle current limiting, as well as
thermal shutdown for full protection under fault conditions.

Features

• 3.3 V, 5.0 V, 12 V, 15 V, and Adjustable Output Versions

• Adjustable Version Output Voltage Range, 1.23 to 37 V ±4%

Maximum Over Line and Load Conditions

• Guaranteed 3.0 A Output Current

• Wide Input Voltage Range

• Requires Only 4 External Components

• 52 kHz Fixed Frequency Internal Oscillator

• TTL Shutdown Capability, Low Power Standby Mode

• High Efficiency

• Uses Readily Available Standard Inductors

• Thermal Shutdown and Current Limit Protection

• Moisture Sensitivity Level (MSL) Equals 1

• Pb−Free Packages are Available

Applications

• Simple High−Efficiency Step−Down (Buck) Regulator

• Efficient Pre−Regulator for Linear Regulators

• On−Card Switching Regulators

• Positive to Negative Converter (Buck−Boost)

• Negative Step−Up Converters

• Power Supply for Battery Chargers

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1

5

Heatsink surface connected to Pin 3

1

5

Pin 1. V

2. Output

3. Ground

4. Feedback

5. ON/OFF

1

5

Heatsink surface (shown as terminal 6 in
case outline drawing) is connected to Pin 3

ORDERING INFORMATION

See detailed ordering and shipping information in the package
dimensions section on page 24 of this data sheet.

DEVICE MARKING INFORMATION

See general marking information in the device marking
section on page 25 of this data sheet.

TO−220

TV SUFFIX

CASE 314B

TO−220

T SUFFIX

CASE 314D

in

D2PAK

D2T SUFFIX

CASE 936A

© Semiconductor Components Industries, LLC, 2006

January, 2006 − Rev. 8

1 Publication Order Number:

LM2576/D

Typical Application (Fixed Output Voltage Versions)

Unregulated

DC Input

LM2576

Feedback

L1

100 mH

D1
1N5822

Driver

Thermal

Shutdown

C

out

1000 mF

1.0 Amp
Switch

5.0 V Regulated
Output 3.0 A Load

ON/OFF

5

Voltage Versions

For adjustable version
R1 = open, R2 = 0 W

Output

2
GND

3

Output

3.3 V

5.0 V

D1

12 V
15 V

L1

R2

(W)

1.7 k

3.1 k

8.84 k

11.3 k

Regulated

Output

V

out

C

out

Load

/OFF5

4

Output

2

7.0 V − 40 V

Unregulated

DC Input

C

100 mF

+V

in

LM2576

1

in

GN

3ON

D

Representative Block Diagram and Typical Application

+V

in

1

C

in

4

Feedback

R2

Fixed Gain
Error Amplifier

R1

1.0 k

Freq
Shift

18 kHz

1.235 V

Band−Gap

Reference

3.1 V Internal

Comparator

52 kHz

Oscillator

Regulator

ON/OFF

Current

Limit

Latch

Reset

This device contains 162 active transistors.

Figure 1. Block Diagram and Typical Application

MAXIMUM RATINGS

Rating Symbol Value Unit

Maximum Supply Voltage V

in

ON/OFF Pin Input Voltage − −0.3 V ≤ V ≤ +V
Output Voltage to Ground (Steady−State) − −1.0 V
Power Dissipation

Case 314B and 314D (TO−220, 5−Lead) P

Thermal Resistance, Junction−to−Ambient
Thermal Resistance, Junction−to−Case

Case 936A (D2PAK) P

Thermal Resistance, Junction−to−Ambient

Thermal Resistance, Junction−to−Case
Storage Temperature Range T
Minimum ESD Rating (Human Body Model: C = 100 pF, R = 1.5 kW)

D

R

q

JA

R

q

JC
D

R

q

JA

R

q

JC

stg

− 2.0 kV
Lead Temperature (Soldering, 10 seconds) − 260 °C
Maximum Junction Temperature T

J

Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit
values (not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied,
damage may occur and reliability may be affected.

45 V

in

Internally Limited W

65 °C/W

5.0 °C/W

Internally Limited W

70 °C/W

5.0 °C/W

−65 to +150 °C

150 °C

V

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2

LM2576

OPERATING RATINGS (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.)

Rating Symbol Value Unit

Operating Junction Temperature Range T
Supply Voltage V

J

in

SYSTEM PARAMETERS (Note 1 Test Circuit Figure 15)

ELECTRICAL CHARACTERISTICS

for the 12 V version, and Vin = 30 V for the 15 V version. I
operating junction temperature range that applies Note 2, unless otherwise noted.)

Characteristics Symbol Min Typ Max Unit

LM2576−3.3 (Note 1 Test Circuit Figure 15)

Output Voltage (Vin = 12 V, I
Output Voltage (6.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

TJ = 25°C 3.168 3.3 3.432
TJ = −40 to +125°C 3.135 − 3.465

Efficiency (V

= 12 V, I

in

LM2576−5 (Note 1 Test Circuit Figure 15)

Output Voltage (Vin = 12 V, I
Output Voltage (8.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

TJ = 25°C 4.8 5.0 5.2
TJ = −40 to +125°C 4.75 − 5.25

Efficiency (Vin = 12 V, I

LM2576−12 (Note 1 Test Circuit Figure 15)

Output Voltage (Vin = 25 V, I
Output Voltage (15 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

TJ = 25°C 11.52 12 12.48
TJ = −40 to +125°C 11.4 − 12.6

Efficiency (Vin = 15 V, I

LM2576−15 (Note 1 Test Circuit Figure 15)

Output Voltage (V

= 30 V, I

in

Output Voltage (18 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

TJ = 25°C 14.4 15 15.6
T

= −40 to +125°C 14.25 − 15.75

J

Efficiency (Vin = 18 V, I

LM2576 ADJUSTABLE VERSION (Note 1 Test Circuit Figure 15)

Feedback Voltage (V
Feedback Voltage (8.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

TJ = 25°C 1.193 1.23 1.267
T

= −40 to +125°C 1.18 − 1.28

J

Efficiency (V

= 12 V, I

in

1. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.
When the LM2576 is used as shown in the Figure 15 test circuit, system performance will be as shown in system parameters section.

2. Tested junction temperature range for the LM2576: T

Load

= 3.0 A) η − 75 − %

Load

Load

= 3.0 A) η − 77 − %

Load

Load

= 3.0 A) η − 88 − %

Load

Load

= 3.0 A) η − 88 − %

Load

= 12 V, I

in

= 3.0 A, V

Load

Load

(Unless otherwise specified, Vin = 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 V

= 500 mA. For typical values T

Load

= 0.5 A, T

= 0.5 A, TJ = 25°C) V

= 0.5 A, TJ = 25°C) V

= 0.5 A, TJ = 25°C) V

= 0.5 A, V

= 25°C) V

J

≤ 3.0 A) V

Load

≤ 3.0 A) V

Load

≤ 3.0 A) V

Load

≤ 3.0 A) V

Load

= 5.0 V, TJ = 25°C) V

out

≤ 3.0 A, V

Load

= 5.0 V) η − 77 − %

out

= 5.0 V) V

out

= −40°C T

low

out
out

out
out

out
out

out
out

out
out

= +125°C

high

= 25°C, for min/max values TJ is the

J

3.234 3.3 3.366 V

4.9 5.0 5.1 V

11.76 12 12.24 V

14.7 15 15.3 V

1.217 1.23 1.243 V

−40 to +125 °C
40 V

V

V

V

V

V

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LM2576

DEVICE PARAMETERS

ELECTRICAL CHARACTERISTICS (Unless otherwise specified, V

for the 12 V version, and Vin = 30 V for the 15 V version. I
operating junction temperature range that applies [Note 2], unless otherwise noted.)

Characteristics Symbol Min Typ Max Unit

ALL OUTPUT VOLTAGE VERSIONS

Feedback Bias Current (V

= 5.0 V Adjustable Version Only) I

out

TJ = 25°C − 25 100
TJ = −40 to +125°C − − 200

Oscillator Frequency Note 3 f

TJ = 25°C − 52 −
TJ = 0 to +125°C 47 − 58
TJ = −40 to +125°C 42 − 63

Saturation Voltage (I

= 3.0 A Note 4) V

out

TJ = 25°C − 1.5 1.8
TJ = −40 to +125°C − − 2.0

Max Duty Cycle (“on”) Note 5 DC 94 98 − %
Current Limit (Peak Current Notes 3 and 4) I

TJ = 25°C 4.2 5.8 6.9
TJ = −40 to +125°C 3.5 − 7.5

Output Leakage Current Notes 6 and 7, TJ = 25°C I

Output = 0 V − 0.8 2.0
Output = −1.0 V − 6.0 20

Quiescent Current Note 6 I

TJ = 25°C − 5.0 9.0
TJ = −40 to +125°C − − 11

Standby Quiescent Current (ON/OFF Pin = 5.0 V (“off”)) I

TJ = 25°C − 80 200
TJ = −40 to +125°C − − 400

ON/OFF Pin Logic Input Level (Test Circuit Figure 15) V

V

= 0 V V

out

TJ = 25°C 2.2 1.4 −
TJ = −40 to +125°C 2.4 − −

V

= Nominal Output Voltage V

out

TJ = 25°C − 1.2 1.0
TJ = −40 to +125°C − − 0.8

ON/OFF Pin Input Current (Test Circuit Figure 15)

ON/OFF Pin = 5.0 V (“off”), TJ = 25°C I
ON/OFF Pin = 0 V (“on”), TJ = 25°C I

3. 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 dissipation of the IC by
lowering the minimum duty cycle from 5% down to approximately 2%.

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

5. Feedback (Pin 4) removed from output and connected to 0 V.

6. Feedback (Pin 4) removed from output and connected to +12 V for the Adjustable, 3.3 V, and 5.0 V versions, and +25 V for the 12 V and
15 V versions, to force the output transistor “off”.

7. V

= 40 V.

in

= 500 mA. For typical values T

Load

= 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 V

in

b

osc

sat

CL

L

Q

stby

IH

IL

= 25°C, for min/max values TJ is the

J

nA

kHz

mA

mA

mA

mA

IH
IL

− 15 30

− 0 5.0

V

A

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4

LM2576

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

1.0

Vin = 20 V

0.8
I

Load

0.6
Normalized at TJ = 25°C

0.4

0.2

0

−0.2

−0.4

−0.6

, OUTPUT VOLTAGE CHANGE (%)

out

−0.8

V

−1.0

Figure 2. Normalized Output Voltage

2.0

1.5

1.0

0.5

INPUT − OUTPUT DIFFERENTIAL (V)

0

1.4

1.2

I

= 500 mA

= 500 mA

1.0

Load

TJ = 25°C

0.8

0.6

3.3 V, 5.0 V and ADJ

0.4

0.2

0

−0.2

, OUTPUT VOLTAGE CHANGE (%)

out

−0.4

V

1251007550250−25−50 403530252015105.00

TJ, JUNCTION TEMPERATURE (°C)

−0.6

Vin, INPUT VOLTAGE (V)

Figure 3. Line Regulation

6.5

I

= 3.0 A

Load

6.0

5.5

, OUTPUT CURRENT (A)
I

5.0

O

4.5

4.0

TJ, JUNCTION TEMPERATURE (°C)

I

= 500 mA

Load

TJ, JUNCTION TEMPERATURE (°C)

L1 = 150 mH
R

= 0.1 W

ind

1251007550250−25−50 1251007550250−25−50

Figure 4. Dropout Voltage Figure 5. Current Limit

12 V and 15 V

Vin = 25 V

, QUIESCENT CURRENT (mA)

Q

I

8.0

6.0

4.0

20

V

= 5.0 V

18

16

out

Measured at
Ground Pin
TJ = 25°C

14

I

= 3.0 A

12

Load

10

I

= 200 mA

Load

403530252015105.00 1251007550250−25−50

Vin, INPUT VOLTAGE (V)

μA)

, STANDBY QUIESCENT CURRENT (

I

stby

200

180

160

140

120

100

V

= 5.0 V

ON/OFF

Vin = 40 V

80

60

Vin = 12 V

40

20

0

TJ, JUNCTION TEMPERATURE (°C)

Figure 6. Quiescent Current Figure 7. Standby Quiescent Current

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LM2576

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

, STANDBY QUIESCENT CURRENT (μA)I

NORMALIZED FREQUENCY (%)

200

180

160

140

120

100

80

60

40

20

stby

0

TJ = 25°C

Vin, INPUT VOLTAGE (V)

40302520151050 0 0.5 1.0 1.5 2.0 3.0

35 2.5

, SATURATION VOLTAGE (V)

V

sat

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

Figure 8. Standby Quiescent Current

8.0

6.0

4.0

2.0

−2.0

−4.0

−6.0

−8.0

−10

Vin = 12 V
Normalized at
25°C

0

1251007550250−25−50 1251007550250−25−50

TJ, JUNCTION TEMPERATURE (°C)

, INPUT VOLTAGE (V)
V

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

in

1.0

0.5

0

Figure 10. Oscillator Frequency Figure 11. Minimum Operating Voltage

−40°C

25°C

125°C

SWITCH CURRENT (A)

Figure 9. Switch Saturation Voltage

Adjustable Version Only

V

' 1.23 V

out

I

= 500 mA

Load

TJ, JUNCTION TEMPERATURE (°C)

, FEEDBACK PIN CURRENT (nA)

b

I

−100

100

−20

−40

−60

−80

80

60

40

20

0

TJ, JUNCTION TEMPERATURE (°C)

Adjustable Version Only

1251007550250−25−50

Figure 12. Feedback Pin Current

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LM2576

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

50 V

A

0

4.0 A

B

2.0 A

0

4.0 A

C

2.0 A

D

0

Figure 13. Switching Waveforms Figure 14. Load Transient Response

Vout = 15 V
A: Output Pin Voltage, 10 V/DIV
B: Inductor Current, 2.0 A/DIV
C: Inductor Current, 2.0 A/DIV, AC−Coupled
D: Output Ripple Voltage, 50 mV/dDIV, AC−Coupled

Horizontal Time Base: 5.0 ms/DIV

Output

Voltage

Change

− 100 mV

Load

Current

100 mV

0

3.0 A

2.0 A

1.0 A

0

100 ms/DIV5 ms/DIV

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7

Fixed Output Voltage Versions

7.0 V − 40 V
Unregulated

DC Input

7.0 V − 40 V
Unregulated

DC Input

LM2576

V

in

LM2576

Fixed Output

1

53ON/OFFGN

C

in

100 mF

V

in

1

C

in

100 mF

D

Cin− 100 mF, 75 V, Aluminium Electrolytic

− 1000 mF, 25 V, Aluminium Electrolytic

C

out

D1 − Schottky, MBR360
L1 − 100 mH, Pulse Eng. PE−92108
R1 − 2.0 k, 0.1%
R2 − 6.12 k, 0.1%

Adjustable Output Voltage Versions

Feedback

LM2576

Adjustable

D

4

Output

2

53ON/OFFGN

Feedback

4

Output

2

L1

100 mH

D1
MBR360

L1

100 mH

D1
MBR360

C

out

1000 mF

C

out

1000 mF

R2

R1

V

Load

out

V

out

5,000 V

Load

V

out

R2 + R1ǒ

Where V
between 1.0 k and 5.0 k

Figure 15. Typical Test Circuit

PCB LAYOUT GUIDELINES

As in any switching regulator, the layout of the printed
circuit board is very important. Rapidly switching currents
associated with wiring inductance, stray capacitance and
parasitic inductance of the printed circuit board traces can
generate voltage transients which can generate
electromagnetic interferences (EMI) and affect the desired
operation. As indicated in the Figure 15, to minimize
inductance and ground loops, the length of the leads
indicated by heavy lines should be kept as short as possible.

For best results, single−point grounding (as indicated) or
ground plane construction should be used.

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+ V

ref

ref

R2

ǒ

1.0 )

V

out

V

ref

= 1.23 V, R1

–1.0Ǔ

R1

Ǔ

On the other hand, the PCB area connected to the Pin 2
(emitter of the internal switch) of the LM2576 should be
kept to a minimum in order to minimize coupling to sensitive
circuitry.

Another sensitive part of the circuit is the feedback. It is
important to keep the sensitive feedback wiring short. To
assure this, physically locate the programming resistors near
to the regulator, when using the adjustable version of the
LM2576 regulator.

8

LM2576

PIN FUNCTION DESCRIPTION

Pin Symbol Description (Refer to Figure 1)

1 V

2 Output This is the emitter of the internal switch. The saturation voltage V

3 GND Circuit ground pin. See the information about the printed circuit board layout.
4 Feedback This pin senses regulated output voltage to complete the feedback loop. The signal is divided by the internal resistor

5 ON/OFF It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total input supply

in

Buck Converter Basics

The LM2576 is a “Buck” or Step−Down Converter which
is the most elementary forward−mode converter. Its basic
schematic can be seen in Figure 16.

The operation of this regulator topology has two distinct
time periods. The first one occurs when the series switch is
on, the input voltage is connected to the input of the inductor.

The output of the inductor is the output voltage, and the
rectifier (or catch diode) is reverse biased. During this
period, since there is a constant voltage source connected
across the inductor, the inductor current begins to linearly
ramp upwards, as described by the following equation:

During this “on” period, energy is stored within the core
material in the form of magnetic flux. If the inductor is
properly designed, there is sufficient energy stored to carry
the requirements of the load during the “off” period.

in

Power
Switch

This pin is the positive input supply for the LM2576 step−down switching regulator. In order to minimize voltage
transients and to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be
present (Cin in Figure 1).

of this output switch is typically 1.5 V. It should
be kept in mind that the PCB area connected to this pin should be kept to a minimum in order to minimize coupling
to sensitive circuitry.

divider network R2, R1 and applied to the non−inverting input of the internal error amplifier. In the Adjustable version
of the LM2576 switching regulator this pin is the direct input of the error amplifier and the resistor network R2, R1 is
connected externally to allow programming of the output voltage.

current to approximately 80 mA. The threshold voltage is typically 1.4 V. Applying a voltage above this value (up to
+Vin) shuts the regulator off. If the voltage applied to this pin is lower than 1.4 V or if this pin is left open, the
regulator will be in the “on” condition.

sat

DESIGN PROCEDURE

This period ends when the power switch is once again
turned on. Regulation of the converter is accomplished by
varying the duty cycle of the power switch. It is possible to
describe the duty cycle as follows:

t

on

d +

, where T is the period of switching.

T

For the buck converter with ideal components, the duty
cycle can also be described as:

V

out

d +

V

in

Figure 17 shows the buck converter, idealized waveforms

I

L(on)

+

ǒ

Vin–V

DV

L

out

L

Ǔ

t

on

C

out

R

Load

of the catch diode voltage and the inductor current.

V

on(SW)

Power
Switch

Off

Diode VoltageInductor Current

VD(FWD)

Power

Switch

On

Power
Switch

Off

Power
Switch

On

Time

Figure 16. Basic Buck Converter

The next period is the “off” period of the power switch.
When the power switch turns off, the voltage across the
inductor reverses its polarity and is clamped at one diode
voltage drop below ground by the catch diode. The current
now flows through the catch diode thus maintaining the load
current loop. This removes the stored energy from the
inductor. The inductor current during this time is:

I

L(off)

+

ǒ

V

out

–V

L

Ǔ

t

D

off

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I

pk

I

min

Diode Diode

Power
Switch

Power
Switch

Figure 17. Buck Converter Idealized Waveforms

9

I

Load

(AV)

Time