ON Semiconductor LM2596 Technical data

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LM2596

3.0 A, Step-Down Switching
Regulator

The LM2596 regulator is monolithic integrated circuit ideally suited
for easy and convenient design of a step−down switching regulator
(buck converter). It is capable of driving a 3.0 A load with excellent
line and load regulation. This device is available in adjustable output
version and it is internally compensated to minimize the number of
external components to simplify the power supply design.

Since LM2596 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.

The LM2596 operates at a switching frequency of 150 kHz thus
allowing smaller sized filter components than what would be needed
with lower frequency switching regulators. Available in a standard
5−lead TO−220 package with several different lead bend options, and

2

D

PAK surface mount package.

The other features include a guaranteed $4% tolerance on output
voltage within specified input voltages and output load conditions, and
$15% on the oscillator frequency. External shutdown is included,
featuring 80 mA (typical) standby current. Self protection features
include switch cycle−by−cycle current limit for the output switch, as
well as thermal shutdown for complete protection under fault
conditions.

Features

• Adjustable Output Voltage Range 1.23 V − 37 V

• Guaranteed 3.0 A Output Load Current

• Wide Input Voltage Range up to 40 V

• 150 kHz Fixed Frequency Internal Oscillator

• TTL Shutdown Capability

• Low Power Standby Mode, typ 80 mA

• Thermal Shutdown and Current Limit Protection

• Internal Loop Compensation

• Moisture Sensitivity Level (MSL) Equals 1

• Pb−Free Packages are Available

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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

1

5

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

TO−220

TV SUFFIX

CASE 314B

TO−220

T SUFFIX

CASE 314D

in

/OFF

2

D

PAK

D2T SUFFIX

CASE 936A

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

© Semiconductor Components Industries, LLC, 2008

November, 2008 − Rev. 0

ORDERING INFORMATION

See detailed ordering and shipping information in the package
dimensions section on page 23 of this data sheet.

DEVICE MARKING INFORMATION

See general marking information in the device marking
section on page 23 of this data sheet.

1 Publication Order Number:

LM2596/D

Unregulated

DC Input

LM2596

Typical Application (Adjustable Output Voltage Version)

C

out

220 mF

R1

1.0k

C

FF

5.0 V Regulated
Output 3.0 A Load

ON

/OFF

5

Output

2
GND

3

D1

Regulated

L1

Output

V

out

C

out

Load

Feedback

12 V

Unregulated

DC Input

C

100 mF

/OFF5

4

Output

2

+V

in

LM2596

1

in

GND

3ON

L1

33 mH

D1
1N5822

R2

3.1k

Block Diagram

+V

in

1

C

in

Feedback

C

FF

4

R1

R2

Fixed Gain
Error Amplifier

Freq
Shift

30 kHz

1.235 V
Band-Gap
Reference

3.1 V Internal

Comparator

150 kHz

Oscillator

Regulator

Current

Latch

Reset

ON

Limit

/OFF

Driver

3.0 Amp
Switch

Thermal

Shutdown

Figure 1. Typical Application and Internal Block Diagram

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

Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.

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

LM2596

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 is the direct input of the error amplifier and the resistor network R2, R1 is connected externally to allow pro-

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

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.)

Operating Junction Temperature Range T

Supply Voltage V

This pin is the positive input supply for the LM2596 step−down switching regulator. In order to minimize voltage transi-

in

ents and to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be present
(C

in Figure 1).

in

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

sat

sensitive circuitry.

gramming of the output voltage.

current to approximately 80 mA. The threshold voltage is typically 1.6 V. Applying a voltage above this value (up to

) shuts the regulator off. If the voltage applied to this pin is lower than 1.6 V or if this pin is left open, the regulator

+V

in

will be in the “on” condition.

Rating

Symbol Value Unit

J

in

−40 to +125 °C

4.5 to 40 V

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3

LM2596

SYSTEM PARAMETERS

ELECTRICAL CHARACTERISTICS Specifications with standard type face are for T

over full Operating Temperature Range −40°C to +125°C

Characteristics Symbol Min Typ Max Unit

LM2596 (Note 1, Test Circuit Figure 15)

Feedback Voltage (V

= 12 V, I

in

Feedback Voltage (8.5 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

Efficiency (V

Feedback Bias Current (V

= 12 V, I

in

Load

out

Oscillator Frequency (Note 2) f

Saturation Voltage (I

= 3.0 A, Notes 3 and 4) V

out

Max Duty Cycle “ON” (Note 4) DC 95 %

Current Limit (Peak Current, Notes 2 and 3) I

Output Leakage Current (Notes 5 and 6)
Output = 0 V
Output = −1.0 V

Quiescent Current (Note 5) I

Standby Quiescent Current (ON/OFF Pin = 5.0 V (“OFF”))
(Note 6)

ON/OFF PIN LOGIC INPUT

Threshold Voltage

V

= 0 V (Regulator OFF) V

out

V

= Nominal Output Voltage (Regulator ON) V

out

ON/OFF Pin Input Current

/OFF Pin = 5.0 V (Regulator OFF) I

ON

ON/OFF Pin = 0 V (regulator ON) I

1. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.
When the LM2596 is used as shown in the Figure 15 test circuit, system performance will be as shown in system parameters section.

2. The oscillator frequency reduces to approximately 30 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%.

3. No diode, inductor or capacitor connected to output (Pin 2) sourcing the current.

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

5. Feedback (Pin 4) removed from output and connected to +12 V to force the output transistor “off”.

= 40 V.

6. V

in

= 0.5 A, V

Load

= 3.0 A, V

out

= 5.0 V, ) V

out

Load

≤ 3.0 A, V

= 5.0 V) V

out

FB_nom

= 5.0 V) η − 73 − %

Characteristics Symbol Min Typ Max Unit

= 5.0 V) I

I

= 25°C, and those with boldface type apply

J

1.23 V

1.193

1.18

135

120

4.2

3.5

25 100

150 165

1.5 1.8

5.6 6.9

0.5

osc

CL

I

FB

b

sat

L

6.0

Q

stby

5.0 10 mA

80 200

1.6 V

IH

IL

IH

IL

2.2

2.4

− 15 30

− 0.01 5.0

1.267

1.28

200

180

2.0

7.5

2.0
20

250

1.0

0.8

V

nA

kHz

V

A

mA

mA

V

V

mA

mA

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4

LM2596

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

1.0

Vin = 20 V

0.8
I

Load

0.6
Normalized at T

0.4

0.2

0

-0.2

-0.4

-0.6

, OUTPUT VOLTAGE CHANGE (%)

out

-0.8

V

-1.0

2.0

1.5

= 500 mA

= 25°C

J

TJ, JUNCTION TEMPERATURE (°C)

Figure 2. Normalized Output Voltage

I

= 3.0 A

Load

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

-0.2

, OUTPUT VOLTAGE CHANGE (%)

out

-0.4

V

1251007550250-25-50 403530252015105.00

-0.6

6.0

5.5

I

Load

T

= 25°C

J

= 500 mA

3.3 V and 5.0 V

, INPUT VOLTAGE (V)

V

in

Figure 3. Line Regulation

12 V and 15 V

Vin = 25 V

INPUT - OUTPUT DIFFERENTIAL (V)

, QUIESCENT CURRENT (mA)

Q

I

1.0

0.5

8.0

6.0

4.0

5.0

I

= 500 mA

Load

, OUTPUT CURRENT (A)

4.5

O

I

L1 = 33 mH

= 0.1 W

R

0

ind

1251007550250-25-50 1251007550250-25-50

TJ, JUNCTION TEMPERATURE (°C)

4.0

TJ, JUNCTION TEMPERATURE (°C)

Figure 4. Dropout Voltage Figure 5. Current Limit

20

V

= 5.0 V

18

16

14

I

= 3.0 A

12

Load

out

Measured at
Ground Pin
T

= 25°C

J

10

I

= 200 mA

Load

403530252015105.00 1251007550250-25-50

, INPUT VOLTAGE (V)

V

in

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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5

LM2596

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

200

180

160

TJ = 25°C

35 2.5

Vin, INPUT VOLTAGE (V)

, STANDBY QUIESCENT CURRENT (μA)I

stby

140

120

100

80

60

40

20

0

Figure 8. Standby Quiescent Current

1.0

0.0

−1.0

−2.0

−3.0

−4.0

−5.0

−6.0

−7.0

NORMALIZED FREQUENCY (%)

−8.0

−9.0

−50 −25 0 25 50 75 100 125

TJ, JUNCTION TEMPERATURE (°C)

VIN = 12 V Normalized
at 25°C

Figure 10. Switching Frequency

1.6

1.4

1.2

-40°C

1.0

0.8

25°C

0.6
125°C

, SATURATION VOLTAGE (V)

0.4

sat

V

0.2

40302520151050 0 0.5 1.0 1.5 2.0 3.0

0

SWITCH CURRENT (A)

Figure 9. Switch Saturation Voltage

5.0

4.5

4.0

3.5

3.0

2.5

2.0

, INPUT VOLTAGE (V)

1.5

in

V

1.0

0.5

0

-50

V

' 1.23 V

out

I

= 500 mA

Load

TJ, JUNCTION TEMPERATURE (°C)

1251007550250-25

Figure 11. Minimum Supply Operating Voltage

, FEEDBACK PIN CURRENT (nA)

b

I

-100

100

-20

-40

-60

-80

80

60

40

20

0

1251007550250-25-50

, JUNCTION TEMPERATURE (°C)

T

J

Figure 12. Feedback Pin Current

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6

LM2596

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

10 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 = 5 V
A: Output Pin Voltage, 10 V/div
B: Switch Current, 2.0 A/div
C: Inductor Current, 2.0 A/div, AC−Coupled
D: Output Ripple Voltage, 50 mV/div, 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/div2 ms/div

8.5 V - 40 V
Unregulated

DC Input

C

in

100 mF

Adjustable Output Voltage Versions

Feedback

V

in

LM2596

1

4

Output

2

/OFFGND

53ON

+ V

ref

= 1.23 V, R1

ref

V

V

ǒ

1.0 )

out

1.0Ǔ

ref

V

out

R2 + R1ǒ

Where V
between 1.0 k and 5.0 k

Figure 15. Typical Test Circuit

L1

33 mH

D1
1N5822

R2

Ǔ

R1

C

out

220 mF

R2

R1

5,000 V

C

FF

V

out

Load

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7

LM2596

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.

DESIGN PROCEDURE

Buck Converter Basics

The LM2596 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:

I

L(on)

+

ǒ

VIN* V

L

OUT

Ǔ

t

on

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.

Power
Switch

L

On the other hand, the PCB area connected to the Pin 2
(emitter of the internal switch) of the LM2596 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
LM2596 regulator.

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
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

in

Figure 16. Basic Buck Converter

DV

C

out

R

Load

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

Figure 17. Buck Converter Idealized Waveforms

8

Power
Switch

Power

Switch

I

Load

Time

(AV)

Time