LM2596
SIMPLE SWITCHER® Power Converter 150 kHz
3A Step-Down Voltage Regulator
General Description
The LM2596 series of regulators are monolithic integrated
circuits that provide all the active functions for a step-down
(buck) switching regulator, capable of driving a 3A load with
excellent line and load regulation. These devices are avail-
able in fixed output voltages of 3.3V, 5V, 12V, and an adjust-
able output version.
Requiring a minimum number of external components, these
regulators are simple to use and include internal frequency
compensation†, and a fixed-frequency oscillator.
The LM2596 series operates at a switching frequency of
150 kHz thus allowing smaller sized filter components than
what would be needed with lower frequency switching regu-
lators. Available in a standard 5-lead TO-220 package with
several different lead bend options, and a 5-lead TO-263
surface mount package.
A standard series of inductors are available from several
different manufacturers optimized for use with the LM2596
series. This feature greatly simplifies the design of
switch-mode power supplies.
Other features include a guaranteed ±4% tolerance on out-
put voltage under specified input voltage and output load
conditions, and ±15% on the oscillator frequency. External
shutdown is included, featuring typically 80 µA standby cur-
rent. Self protection features include a two stage frequency
reducing current limit for the output switch and an over
temperature shutdown for complete protection under fault
conditions.
Features
n 3.3V, 5V, 12V, and adjustable output versions
n Adjustable version output voltage range, 1.2V to 37V
±4% max over line and load conditions
n Available in TO-220 and TO-263 packages
n Guaranteed 3A output load current
n Input voltage range up to 40V
n Requires only 4 external components
n Excellent line and load regulation specifications
n 150 kHz fixed frequency internal oscillator
n TTL shutdown capability
n Low power standby mode, IQ typically 80 µA
n High efficiency
n Uses readily available standard inductors
n Thermal shutdown and current limit protection
Applications
n Simple high-efficiency step-down (buck) regulator
n On-card switching regulators
n Positive to negative converter
Note: †Patent Number 5,382,918.
Typical Application (Fixed Output Voltage
Versions)
01258301
SIMPLE SWITCHER® and Switchers Made Simple® are registered trademarks of National Semiconductor Corporation.
May 2002
LM
2596
SIM
PLE
SW
ITCHER
Pow
erConverter150
kHz
3A
Step-Down
V
oltage
Regulator
© 2002 National Semiconductor Corporation DS012583 www.national.com
Connection Diagrams and Ordering Information
Bent and Staggered Leads, Through Hole
Package
5-Lead TO-220 (T)
Surface Mount Package
5-Lead TO-263 (S)
01258302
Order Number LM2596T-3.3, LM2596T-5.0,
LM2596T-12 or LM2596T-ADJ
See NS Package Number T05D
01258303
Order Number LM2596S-3.3, LM2596S-5.0,
LM2596S-12 or LM2596S-ADJ
See NS Package Number TS5B
LM
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Maximum Supply Voltage 45V
ON /OFF Pin Input Voltage −0.3 ≤ V ≤ +25V
Feedback Pin Voltage −0.3 ≤ V ≤+25V
Output Voltage to Ground
(Steady State) −1V
Power Dissipation Internally limited
Storage Temperature Range −65˚C to +150˚C
ESD Susceptibility
Human Body Model (Note 2) 2 kV
Lead Temperature
S Package
Vapor Phase (60 sec.) +215˚C
Infrared (10 sec.) +245˚C
T Package (Soldering, 10 sec.) +260˚C
Maximum Junction Temperature +150˚C
Operating Conditions
Temperature Range −40˚C ≤ TJ ≤ +125˚C
Supply Voltage 4.5V to 40V
LM2596-3.3
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range
Symbol Parameter Conditions
LM2596-3.3
Units
(Limits)Typ(Note 3)
Limit
(Note 4)
SYSTEM PARAMETERS (Note 5) Test Circuit Figure 1
VOUT Output Voltage 4.75V ≤ VIN ≤ 40V, 0.2A ≤ ILOAD ≤ 3A 3.3 V
3.168/3.135 V(min)
3.432/3.465 V(max)
η Efficiency VIN = 12V, ILOAD = 3A 73 %
LM2596-5.0
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range
Symbol Parameter Conditions
LM2596-5.0
Units
(Limits)Typ(Note 3)
Limit
(Note 4)
SYSTEM PARAMETERS (Note 5) Test Circuit Figure 1
VOUT Output Voltage 7V ≤ VIN ≤ 40V, 0.2A ≤ ILOAD ≤ 3A 5.0 V
4.800/4.750 V(min)
5.200/5.250 V(max)
η Efficiency VIN = 12V, ILOAD = 3A 80 %
LM2596-12
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range
Symbol Parameter Conditions
LM2596-12
Units
(Limits)Typ(Note 3)
Limit
(Note 4)
SYSTEM PARAMETERS (Note 5) Test Circuit Figure 1
VOUT Output Voltage 15V ≤ VIN ≤ 40V, 0.2A ≤ ILOAD ≤ 3A 12.0 V
11.52/11.40 V(min)
12.48/12.60 V(max)
η Efficiency VIN = 25V, ILOAD = 3A 90 %
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LM2596-ADJ
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range
Symbol Parameter Conditions
LM2596-ADJ
Units
(Limits)Typ(Note 3)
Limit
(Note 4)
SYSTEM PARAMETERS (Note 5) Test Circuit Figure 1
VFB Feedback Voltage 4.5V ≤ VIN ≤ 40V, 0.2A ≤ ILOAD ≤ 3A 1.230 V
VOUT programmed for 3V. Circuit of Figure 1 1.193/1.180 V(min)
1.267/1.280 V(max)
η Efficiency VIN = 12V, VOUT = 3V, ILOAD = 3A 73 %
All Output Voltage Versions
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable version and VIN = 24V for the 12V ver-
sion. ILOAD = 500 mA
Symbol Parameter Conditions
LM2596-XX
Units
(Limits)Typ(Note 3)
Limit
(Note 4)
DEVICE PARAMETERS
Ib Feedback Bias Current Adjustable Version Only, VFB = 1.3V 10 nA
50/100 nA (max)
fO Oscillator Frequency (Note 6) 150 kHz
127/110 kHz(min)
173/173 kHz(max)
VSAT Saturation Voltage IOUT = 3A (Notes 7, 8) 1.16 V
1.4/1.5 V(max)
DC Max Duty Cycle (ON) (Note 8) 100 %
Min Duty Cycle (OFF) (Note 9) 0
ICL Current Limit Peak Current (Notes 7, 8) 4.5 A
3.6/3.4 A(min)
6.9/7.5 A(max)
IL Output Leakage Current Output = 0V (Notes 7, 9) 50 µA(max)
Output = −1V (Note 10) 2 mA
30 mA(max)
IQ Quiescent Current (Note 9) 5 mA
10 mA(max)
ISTBY Standby Quiescent Current ON/OFF pin = 5V (OFF) (Note 10) 80 µA
200/250 µA(max)
θJC Thermal Resistance TO-220 or TO-263 Package, Junction to Case 2 ˚C/W
θJA TO-220 Package, Junction to Ambient (Note 11) 50 ˚C/W
θJA TO-263 Package, Junction to Ambient (Note 12) 50 ˚C/W
θJA TO-263 Package, Junction to Ambient (Note 13) 30 ˚C/W
θJA TO-263 Package, Junction to Ambient (Note 14) 20 ˚C/W
ON/OFF CONTROL Test Circuit Figure 1
ON /OFF Pin Logic Input 1.3 V
VIH Threshold Voltage Low (Regulator ON) 0.6 V(max)
VIL High (Regulator OFF) 2.0 V(min)
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All Output Voltage Versions
Electrical Characteristics (Continued)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable version and VIN = 24V for the 12V ver-
sion. ILOAD = 500 mA
Symbol Parameter Conditions
LM2596-XX
Units
(Limits)Typ(Note 3)
Limit
(Note 4)
IH ON /OFF Pin Input Current VLOGIC = 2.5V (Regulator OFF) 5 µA
15 µA(max)
IL VLOGIC = 0.5V (Regulator ON) 0.02 µA
5 µA(max)
Note 1: Absolute Maximum Ratings 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: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin.
Note 3: Typical numbers are at 25˚C and represent the most likely norm.
Note 4: 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 extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to
calculate Average Outgoing Quality Level (AOQL).
Note 5: External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator
system performance. When the LM2596 is used as shown in the Figure 1 test circuit, system performance will be as shown in system parameters section of Electrical
Characteristics.
Note 6: The switching frequency is reduced when the second stage current limit is activated.
Note 7: No diode, inductor or capacitor connected to output pin.
Note 8: Feedback pin removed from output and connected to 0V to force the output transistor switch ON.
Note 9: Feedback pin removed from output and connected to 12V for the 3.3V, 5V, and the ADJ. version, and 15V for the 12V version, to force the output transistor
switch OFF.
Note 10: VIN = 40V.
Note 11: Junction to ambient thermal resistance (no external heat sink) for the TO-220 package mounted vertically, with the leads soldered to a printed circuit board
with (1 oz.) copper area of approximately 1 in2.
Note 12: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single printed circuit board with 0.5 in2 of (1 oz.) copper area.
Note 13: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 2.5 in2 of (1 oz.) copper area.
Note 14: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in2 of (1 oz.) copper area on
the LM2596S side of the board, and approximately 16 in2 of copper on the other side of the p-c board. See Application Information in this data sheet and the thermal
model in Switchers Made Simple™ version 4.3 software.
Typical Performance Characteristics (Circuit of Figure 1)
Normalized
Output Voltage Line Regulation Efficiency
01258304 01258305 01258306
LM
2596
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Typical Performance Characteristics (Circuit of Figure 1) (Continued)
Switch Saturation
Voltage Switch Current Limit Dropout Voltage
01258307 01258308 01258309
Operating
Quiescent Current
Shutdown
Quiescent Current
Minimum Operating
Supply Voltage
01258310 01258311 01258312
ON /OFF Threshold
Voltage
ON /OFF Pin
Current (Sinking) Switching Frequency
01258313 01258314 01258315
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Typical Performance Characteristics (Circuit of Figure 1) (Continued)
Feedback Pin
Bias Current
01258316
LM
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Typical Performance Characteristics
Continuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 2A
L = 32 µH, COUT = 220 µF, COUT ESR = 50 mΩ
Discontinuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 500 mA
L = 10 µH, COUT = 330 µF, COUT ESR = 45 mΩ
01258317
Horizontal Time Base: 2 µs/div.
A: Output Pin Voltage, 10V/div.
B: Inductor Current 1A/div.
C: Output Ripple Voltage, 50 mV/div.
01258318
Horizontal Time Base: 2 µs/div.
A: Output Pin Voltage, 10V/div.
B: Inductor Current 0.5A/div.
C: Output Ripple Voltage, 100 mV/div.
Load Transient Response for Continuous Mode
VIN = 20V, VOUT = 5V, ILOAD = 500 mA to 2A
L = 32 µH, COUT = 220 µF, COUT ESR = 50 mΩ
Load Transient Response for Discontinuous Mode
VIN = 20V, VOUT = 5V, ILOAD = 500 mA to 2A
L = 10 µH, COUT = 330 µF, COUT ESR = 45 mΩ
01258319
Horizontal Time Base: 100 µs/div.
A: Output Voltage, 100 mV/div. (AC)
B: 500 mA to 2A Load Pulse
01258320
Horizontal Time Base: 200 µs/div.
A: Output Voltage, 100 mV/div. (AC)
B: 500 mA to 2A Load Pulse
Test Circuit and Layout Guidelines
Fixed Output Voltage Versions
01258322
CIN — 470 µF, 50V, Aluminum Electrolytic Nichicon “PL Series”
COUT — 220 µF, 25V Aluminum Electrolytic, Nichicon “PL Series”
D1 — 5A, 40V Schottky Rectifier, 1N5825
L1 — 68 µH, L38
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Test Circuit and Layout Guidelines (Continued)
As in any switching regulator, layout is very important. Rap-
idly switching currents associated with wiring inductance can
generate voltage transients which can cause problems. For
minimal inductance and ground loops, the wires indicated by
heavy lines should be wide printed circuit traces and
should be kept as short as possible. For best results,
external components should be located as close to the
switcher lC as possible using ground plane construction or
single point grounding.
If open core inductors are used, special care must be
taken as to the location and positioning of this type of induc-
tor. Allowing the inductor flux to intersect sensitive feedback,
lC groundpath and COUT wiring can cause problems.
When using the adjustable version, special care must be
taken as to the location of the feedback resistors and the
associated wiring. Physically locate both resistors near the
IC, and route the wiring away from the inductor, especially an
open core type of inductor. (See application section for more
information.)
Adjustable Output Voltage Versions
01258323
where VREF = 1.23V
Select R1 to be approximately 1 kΩ, use a 1% resistor for best stability.
CIN — 470 µF, 50V, Aluminum Electrolytic Nichicon “PL Series”
COUT — 220 µF, 35V Aluminum Electrolytic, Nichicon “PL Series”
D1 — 5A, 40V Schottky Rectifier, 1N5825
L1 — 68 µH, L38
R1 — 1 kΩ, 1%
CFF — See Application Information Section
FIGURE 1. Standard Test Circuits and Layout Guides
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LM2596 Series Buck Regulator Design Procedure (Fixed Output)
PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)
Given:
VOUT = Regulated Output Voltage (3.3V, 5V or 12V)
VIN(max) = Maximum DC Input Voltage
ILOAD(max) = Maximum Load Current
Given:
VOUT = 5V
VIN(max) = 12V
ILOAD(max) = 3A
1. Inductor Selection (L1)
A. Select the correct inductor value selection guide from Fig-
ures Figure 4, Figure 5, or Figure 6. (Output voltages of 3.3V,
5V, or 12V respectively.) For all other voltages, see the design
procedure for the adjustable version.
B. From the inductor value selection guide, identify the induc-
tance region intersected by the Maximum Input Voltage line
and the Maximum Load Current line. Each region is identified
by an inductance value and an inductor code (LXX).
C. Select an appropriate inductor from the four manufacturer’s
part numbers listed in Figure 8.
1. Inductor Selection (L1)
A. Use the inductor selection guide for the 5V version shown
in Figure 5.
B. From the inductor value selection guide shown in Figure 5,
the inductance region intersected by the 12V horizontal line
and the 3A vertical line is 33 µH, and the inductor code is L40.
C. The inductance value required is 33 µH. From the table in
Figure 8, go to the L40 line and choose an inductor part
number from any of the four manufacturers shown. (In most
instance, both through hole and surface mount inductors are
available.)
2. Output Capacitor Selection (COUT)
A. In the majority of applications, low ESR (Equivalent Series
Resistance) electrolytic capacitors between 82 µF and 820 µF
and low ESR solid tantalum capacitors between 10 µF and
470 µF provide the best results. This capacitor should be
located close to the IC using short capacitor leads and short
copper traces. Do not use capacitors larger than 820 µF .
For additional information, see section on output capaci-
tors in application information section.
B. To simplify the capacitor selection procedure, refer to the
quick design component selection table shown in Figure 2.
This table contains different input voltages, output voltages,
and load currents, and lists various inductors and output ca-
pacitors that will provide the best design solutions.
C. The capacitor voltage rating for electrolytic capacitors
should be at least 1.5 times greater than the output voltage,
and often much higher voltage ratings are needed to satisfy
the low ESR requirements for low output ripple voltage.
D. For computer aided design software, see Switchers Made
Simple™ version 4.3 or later.
2. Output Capacitor Selection (COUT)
A. See section on output capacitors in application infor-
mation section.
B. From the quick design component selection table shown in
Figure 2, locate the 5V output voltage section. In the load
current column, choose the load current line that is closest to
the current needed in your application, for this example, use
the 3A line. In the maximum input voltage column, select the
line that covers the input voltage needed in your application, in
this example, use the 15V line. Continuing on this line are
recommended inductors and capacitors that will provide the
best overall performance.
The capacitor list contains both through hole electrolytic and
surface mount tantalum capacitors from four different capaci-
tor manufacturers. It is recommended that both the manufac-
turers and the manufacturer’s series that are listed in the table
be used.
In this example aluminum electrolytic capacitors from several
different manufacturers are available with the range of ESR
numbers needed.
330 µF 35V Panasonic HFQ Series
330 µF 35V Nichicon PL Series
C. For a 5V output, a capacitor voltage rating at least 7.5V or
more is needed. But even a low ESR, switching grade, 220 µF
10V aluminum electrolytic capacitor would exhibit approxi-
mately 225 mΩ of ESR (see the curve in Figure 14 for the ESR
vs voltage rating). This amount of ESR would result in rela-
tively high output ripple voltage. To reduce the ripple to 1% of
the output voltage, or less, a capacitor with a higher value or
with a higher voltage rating (lower ESR) should be selected. A
16V or 25V capacitor will reduce the ripple voltage by approxi-
mately half.
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LM2596 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version)
3. Catch Diode Selection (D1)
A. The catch diode current rating must be at least 1.3 times
greater than the maximum load current. Also, if the power
supply design must withstand a continuous output short, the
diode should have a current rating equal to the maximum
current limit of the LM2596. The most stressful condition for
this diode is an overload or shorted output condition.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
C. This diode must be fast (short reverse recovery time) and
must be located close to the LM2596 using short leads and
short printed circuit traces. Because of their fast switching
speed and low forward voltage drop, Schottky diodes provide
the best performance and efficiency, and should be the first
choice, especially in low output voltage applications. Ultra-fast
recovery, or High-Efficiency rectifiers also provide good re-
sults. Ultra-fast recovery diodes typically have reverse recov-
ery times of 50 ns or less. Rectifiers such as the 1N5400
series are much too slow and should not be used.
3. Catch Diode Selection (D1)
A. Refer to the table shown in Figure 11. In this example, a 5A,
20V, 1N5823 Schottky diode will provide the best perfor-
mance, and will not be overstressed even for a shorted output.
4. Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is needed
between the input pin and ground pin to prevent large voltage
transients from appearing at the input. This capacitor should
be located close to the IC using short leads. In addition, the
RMS current rating of the input capacitor should be selected to
be at least 1⁄2 the DC load current. The capacitor manufactur-
ers data sheet must be checked to ass
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