LM2576,LM2576HV
LM2576/LM2576HV Series SIMPLE SWITCHER 3A Step-Down Voltage Regulator
Literature Number: SNVS107B
LM2576/LM2576HV Series
SIMPLE SWITCHER®3A Step-Down Voltage Regulator
General Description
The LM2576 series of regulators are monolithic integrated
circuits that provide all the active functions for a step-down
(buck) switching regulator, capable of driving 3A load with
excellent line and load regulation. These devices are avail-
able in fixed output voltages of 3.3V, 5V, 12V, 15V, and an
adjustable 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 LM2576 series offers a high-efficiency replacement for
popular three-terminal linear regulators. It substantially re-
duces the size of the heat sink, and in some cases no heat
sink is required.
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.
Other features include a guaranteed ±4% tolerance on out-
put voltage within specified input voltages and output load
conditions, and ±10% on the oscillator frequency. External
shutdown is included, featuring 50 µA (typical) standby cur-
rent. The output switch includes cycle-by-cycle current limit-
ing, as well as thermal shutdown for full protection under
fault conditions.
Features
n3.3V, 5V, 12V, 15V, and adjustable output versions
nAdjustable version output voltage range,
1.23V to 37V (57V for HV version) ±4% max over
line and load conditions
nGuaranteed 3A output current
nWide input voltage range, 40V up to 60V for
HV version
nRequires only 4 external components
n52 kHz fixed frequency internal oscillator
nTTL shutdown capability, low power standby mode
nHigh efficiency
nUses readily available standard inductors
nThermal shutdown and current limit protection
nP+ Product Enhancement tested
Applications
nSimple high-efficiency step-down (buck) regulator
nEfficient pre-regulator for linear regulators
nOn-card switching regulators
nPositive to negative converter (Buck-Boost)
Typical Application (Fixed Output Voltage
Versions)
SIMPLE SWITCHER®is a registered trademark of National Semiconductor Corporation.
01147601
FIGURE 1.
August 2004
LM2576/LM2576HV Series SIMPLE SWITCHER 3A Step-Down Voltage Regulator
© 2004 National Semiconductor Corporation DS011476 www.national.com
Block Diagram
01147602
3.3V R2 = 1.7k
5V, R2 = 3.1k
12V, R2 = 8.84k
15V, R2 = 11.3k
For ADJ. Version
R1 = Open, R2 = 0Ω
Patent Pending
Ordering Information
Temperature
Range
Output Voltage NS Package Package
Type
3.3 5.0 12 15 ADJ Number
−40˚C ≤T
A
≤125˚C
LM2576HVS-3.3 LM2576HVS-5.0 LM2576HVS-12 LM2576HVS-15 LM2576HVS-ADJ TS5B TO-263
LM2576S-3.3 LM2576S-5.0 LM2576S-12 LM2576S-15 LM2576S-ADJ
LM2576HVSX-3.3 LM2576HVSX-5.0 LM2576HVSX-12 LM2576HVSX-15 LM2576HVSX-ADJ TS5B
Tape & Reel
LM2576SX-3.3 LM2576SX-5.0 LM2576SX-12 LM2576SX-15 LM2576SX-ADJ
LM2576HVT-3.3 LM2576HVT-5.0 LM2576HVT-12 LM2576HVT-15 LM2576HVT-ADJ T05A TO-220
LM2576T-3.3 LM2576T-5.0 LM2576T-12 LM2576T-15 LM2576T-ADJ
LM2576HVT-3.3 LM2576HVT-5.0 LM2576HVT-12 LM2576HVT-15 LM2576HVT-ADJ T05D
Flow LB03 Flow LB03 Flow LB03 Flow LB03 Flow LB03
LM2576T-3.3 LM2576T-5.0 LM2576T-12 LM2576T-15 LM2576T-ADJ
Flow LB03 Flow LB03 Flow LB03 Flow LB03 Flow LB03
LM2576/LM2576HV
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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
LM2576 45V
LM2576HV 63V
ON /OFF Pin Input Voltage −0.3V ≤V≤+V
IN
Output Voltage to Ground
(Steady State) −1V
Power Dissipation Internally Limited
Storage Temperature Range −65˚C to +150˚C
Maximum Junction Temperature 150˚C
Minimum ESD Rating
(C = 100 pF, R = 1.5 kΩ)2kV
Lead Temperature
(Soldering, 10 Seconds) 260˚C
Operating Ratings
Temperature Range
LM2576/LM2576HV −40˚C ≤T
J
≤+125˚C
Supply Voltage
LM2576 40V
LM2576HV 60V
LM2576-3.3, LM2576HV-3.3
Electrical Characteristics
Specifications with standard type face are for T
J
= 25˚C, and those with boldface type apply over full Operating Temperature
Range.
Symbol Parameter Conditions LM2576-3.3 Units
(Limits)
LM2576HV-3.3
Typ Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
V
OUT
Output Voltage V
IN
= 12V, I
LOAD
= 0.5A 3.3 V
Circuit of Figure 2 3.234 V(Min)
3.366 V(Max)
V
OUT
Output Voltage 6V ≤V
IN
≤40V, 0.5A ≤I
LOAD
≤3A 3.3 V
LM2576 Circuit of Figure 2 3.168/3.135 V(Min)
3.432/3.465 V(Max)
V
OUT
Output Voltage 6V ≤V
IN
≤60V, 0.5A ≤I
LOAD
≤3A 3.3 V
LM2576HV Circuit of Figure 2 3.168/3.135 V(Min)
3.450/3.482 V(Max)
ηEfficiency V
IN
= 12V, I
LOAD
=3A 75 %
LM2576-5.0, LM2576HV-5.0
Electrical Characteristics
Specifications with standard type face are for T
J
= 25˚C, and those with Figure 2 boldface type apply over full Operating Tem-
perature Range.
Symbol Parameter Conditions LM2576-5.0 Units
(Limits)
LM2576HV-5.0
Typ Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
V
OUT
Output Voltage V
IN
= 12V, I
LOAD
= 0.5A 5.0 V
Circuit of Figure 2 4.900 V(Min)
5.100 V(Max)
V
OUT
Output Voltage 0.5A ≤I
LOAD
≤3A, 5.0 V
LM2576 8V ≤V
IN
≤40V 4.800/4.750 V(Min)
Circuit of Figure 2 5.200/5.250 V(Max)
V
OUT
Output Voltage 0.5A ≤I
LOAD
≤3A, 5.0 V
LM2576HV 8V ≤V
IN
≤60V 4.800/4.750 V(Min)
Circuit of Figure 2 5.225/5.275 V(Max)
LM2576/LM2576HV
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LM2576-5.0, LM2576HV-5.0
Electrical Characteristics (Continued)
Specifications with standard type face are for T
J
= 25˚C, and those with Figure 2 boldface type apply over full Operating Tem-
perature Range.
Symbol Parameter Conditions LM2576-5.0 Units
(Limits)
LM2576HV-5.0
Typ Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
ηEfficiency V
IN
= 12V, I
LOAD
=3A 77 %
LM2576-12, LM2576HV-12
Electrical Characteristics
Specifications with standard type face are for T
J
= 25˚C, and those with boldface type apply over full Operating Temperature
Range.
Symbol Parameter Conditions LM2576-12 Units
(Limits)
LM2576HV-12
Typ Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
V
OUT
Output Voltage V
IN
= 25V, I
LOAD
= 0.5A 12 V
Circuit of Figure 2 11.76 V(Min)
12.24 V(Max)
V
OUT
Output Voltage 0.5A ≤I
LOAD
≤3A, 12 V
LM2576 15V ≤V
IN
≤40V 11.52/11.40 V(Min)
Circuit of Figure 2 12.48/12.60 V(Max)
V
OUT
Output Voltage 0.5A ≤I
LOAD
≤3A, 12 V
LM2576HV 15V ≤V
IN
≤60V 11.52/11.40 V(Min)
Circuit of Figure 2 12.54/12.66 V(Max)
ηEfficiency V
IN
= 15V, I
LOAD
=3A 88 %
LM2576-15, LM2576HV-15
Electrical Characteristics
Specifications with standard type face are for T
J
= 25˚C, and those with boldface type apply over full Operating Temperature
Range.
Symbol Parameter Conditions LM2576-15 Units
(Limits)
LM2576HV-15
Typ Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
V
OUT
Output Voltage V
IN
= 25V, I
LOAD
= 0.5A 15 V
Circuit of Figure 2 14.70 V(Min)
15.30 V(Max)
V
OUT
Output Voltage 0.5A ≤I
LOAD
≤3A, 15 V
LM2576 18V ≤V
IN
≤40V 14.40/14.25 V(Min)
Circuit of Figure 2 15.60/15.75 V(Max)
V
OUT
Output Voltage 0.5A ≤I
LOAD
≤3A, 15 V
LM2576HV 18V ≤V
IN
≤60V 14.40/14.25 V(Min)
Circuit of Figure 2 15.68/15.83 V(Max)
ηEfficiency V
IN
= 18V, I
LOAD
=3A 88 %
LM2576/LM2576HV
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LM2576-ADJ, LM2576HV-ADJ
Electrical Characteristics
Specifications with standard type face are for T
J
= 25˚C, and those with boldface type apply over full Operating Temperature
Range.
Symbol Parameter Conditions LM2576-ADJ Units
(Limits)
LM2576HV-ADJ
Typ Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
V
OUT
Feedback Voltage V
IN
= 12V, I
LOAD
= 0.5A 1.230 V
V
OUT
= 5V, 1.217 V(Min)
Circuit of Figure 2 1.243 V(Max)
V
OUT
Feedback Voltage 0.5A ≤I
LOAD
≤3A, 1.230 V
LM2576 8V ≤V
IN
≤40V 1.193/1.180 V(Min)
V
OUT
= 5V, Circuit of Figure 2 1.267/1.280 V(Max)
V
OUT
Feedback Voltage 0.5A ≤I
LOAD
≤3A, 1.230 V
LM2576HV 8V ≤V
IN
≤60V 1.193/1.180 V(Min)
V
OUT
= 5V, Circuit of Figure 2 1.273/1.286 V(Max)
ηEfficiency V
IN
= 12V, I
LOAD
= 3A, V
OUT
=5V 77 %
All Output Voltage Versions
Electrical Characteristics
Specifications with standard type face are for T
J
= 25˚C, and those with boldface type apply over full Operating Temperature
Range. Unless otherwise specified, V
IN
= 12V for the 3.3V, 5V, and Adjustable version, V
IN
= 25V for the 12V version, and V
IN
= 30V for the 15V version. I
LOAD
= 500 mA.
Symbol Parameter Conditions LM2576-XX Units
(Limits)
LM2576HV-XX
Typ Limit
(Note 2)
DEVICE PARAMETERS
I
b
Feedback Bias Current V
OUT
= 5V (Adjustable Version Only) 50 100/500 nA
f
O
Oscillator Frequency (Note 11) 52 kHz
47/42 kHz
(Min)
58/63 kHz
(Max)
V
SAT
Saturation Voltage I
OUT
= 3A (Note 4) 1.4 V
1.8/2.0 V(Max)
DC Max Duty Cycle (ON) (Note 5) 98 %
93 %(Min)
I
CL
Current Limit (Notes 4, 11) 5.8 A
4.2/3.5 A(Min)
6.9/7.5 A(Max)
I
L
Output Leakage Current (Notes 6, 7): Output = 0V 2 mA(Max)
Output = −1V 7.5 mA
Output = −1V 30 mA(Max)
I
Q
Quiescent Current (Note 6) 5 mA
10 mA(Max)
I
STBY
Standby Quiescent ON /OFF Pin = 5V (OFF) 50 µA
Current 200 µA(Max)
LM2576/LM2576HV
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All Output Voltage Versions
Electrical Characteristics (Continued)
Specifications with standard type face are for T
J
= 25˚C, and those with boldface type apply over full Operating Temperature
Range. Unless otherwise specified, V
IN
= 12V for the 3.3V, 5V, and Adjustable version, V
IN
= 25V for the 12V version, and V
IN
= 30V for the 15V version. I
LOAD
= 500 mA.
Symbol Parameter Conditions LM2576-XX Units
(Limits)
LM2576HV-XX
Typ Limit
(Note 2)
DEVICE PARAMETERS
θ
JA
Thermal Resistance T Package, Junction to Ambient (Note 8) 65
θ
JA
T Package, Junction to Ambient (Note 9) 45 ˚C/W
θ
JC
T Package, Junction to Case 2
θ
JA
S Package, Junction to Ambient (Note 10) 50
ON /OFF CONTROL Test Circuit Figure 2
V
IH
ON /OFF Pin V
OUT
= 0V 1.4 2.2/2.4 V(Min)
V
IL
Logic Input Level V
OUT
= Nominal Output Voltage 1.2 1.0/0.8 V(Max)
I
IH
ON /OFF Pin Input ON /OFF Pin = 5V (OFF) 12 µA
Current 30 µA(Max)
I
IL
ON /OFF Pin = 0V (ON) 0µA
10 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: 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.
Note 3: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the
LM2576/LM2576HV is used as shown in the Figure 2 test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.
Note 4: Output pin sourcing current. No diode, inductor or capacitor connected to output.
Note 5: Feedback pin removed from output and connected to 0V.
Note 6: Feedback pin removed from output and connected to +12V for the Adjustable, 3.3V, and 5V versions, and +25V for the 12V and 15V versions, to force the
output transistor OFF.
Note 7: VIN = 40V (60V for high voltage version).
Note 8: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with
1
⁄
2
inch leads in a socket, or on a PC
board with minimum copper area.
Note 9: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with
1
⁄
4
inch leads soldered to a PC board
containing approximately 4 square inches of copper area surrounding the leads.
Note 10: If the TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package. Using
0.5 square inches of copper area, θJA is 50˚C/W, with 1 square inch of copper area, θJA is 37˚C/W, and with 1.6 or more square inches of copper area, θJA is 32˚C/W.
Note 11: The oscillator frequency reduces to approximately 11 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 power dissipation of the IC by lowering the minimum duty cycle
from 5% down to approximately 2%.
Typical Performance Characteristics
(Circuit of Figure 2)
Normalized Output Voltage Line Regulation
01147627 01147628
LM2576/LM2576HV
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Typical Performance Characteristics (Circuit of Figure 2) (Continued)
Efficiency Minimum Operating Voltage
01147635 01147636
Quiescent Current
vs Duty Cycle
Feedback Voltage
vs Duty Cycle
01147637 01147638
Minimum Operating Voltage
Quiescent Current
vs Duty Cycle
01147636 01147637
LM2576/LM2576HV
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Typical Performance Characteristics (Circuit of Figure 2) (Continued)
Feedback Voltage
vs Duty Cycle Feedback Pin Current
01147638
01147604
Maximum Power Dissipation
(TO-263) (See Note 10) Switching Waveforms
01147624 01147606
VOUT = 15V
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: 5 µs/div
Load Transient Response
01147605
LM2576/LM2576HV
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Test Circuit and Layout Guidelines
As in any switching regulator, layout is very important. Rap-
idly switching currents associated with wiring inductance
generate voltage transients which can cause problems. For
minimal 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 con-
struction should be used for best results. When using the
Adjustable version, physically locate the programming resis-
tors near the regulator, to keep the sensitive feedback wiring
short.
Fixed Output Voltage Versions
01147607
CIN — 100 µF, 75V, Aluminum Electrolytic
COUT — 1000 µF, 25V, Aluminum Electrolytic
D1— Schottky, MBR360
L1— 100 µH, Pulse Eng. PE-92108
R1— 2k, 0.1%
R2— 6.12k, 0.1%
Adjustable Output Voltage Version
01147608
where VREF = 1.23V, R1 between 1k and 5k.
FIGURE 2.
LM2576/LM2576HV
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LM2576 Series Buck Regulator
Design Procedure
PROCEDURE (Fixed Output Voltage Versions) EXAMPLE (Fixed Output Voltage Versions)
Given: V
OUT
= Regulated Output Voltage (3.3V, 5V, 12V,
or 15V) V
IN
(Max) = Maximum Input Voltage I
LOAD
(Max) =
Maximum Load Current
Given: V
OUT
=5VV
IN
(Max) = 15V I
LOAD
(Max) = 3A
1. Inductor Selection (L1)
A. Select the correct Inductor value selection guide from
Figures 3, 4, 5 or Figure 6. (Output voltages of 3.3V, 5V,
12V or 15V respectively). For other output voltages, see
the design procedure for the adjustable version.
B. From the inductor value selection guide, identify the
inductance region intersected by V
IN
(Max) and
I
LOAD
(Max), and note the inductor code for that region.
C. Identify the inductor value from the inductor code, and
select an appropriate inductor from the table shown in
Figure 3. Part numbers are listed for three inductor
manufacturers. The inductor chosen must be rated for
operation at the LM2576 switching frequency (52 kHz)
and for a current rating of 1.15 x I
LOAD
. For additional
inductor information, see the inductor section in the
Application Hints section of this data sheet.
1. Inductor Selection (L1)
A. Use the selection guide shown in Figure 4.
B. From the selection guide, the inductance area
intersected by the 15V line and 3A line is L100.
C. Inductor value required is 100 µH. From the table in
Figure 3. Choose AIE 415-0930, Pulse Engineering
PE92108, or Renco RL2444.
2. Output Capacitor Selection (C
OUT
)
A. The value of the output capacitor together with the
inductor defines the dominate pole-pair of the switching
regulator loop. For stable operation and an acceptable
output ripple voltage, (approximately 1% of the output
voltage) a value between 100 µF and 470 µF is
recommended.
B. The capacitor’s voltage rating should be at least 1.5
times greater than the output voltage. For a 5V regulator,
a rating of at least 8V is appropriate, and a 10V or 15V
rating is recommended.
Higher voltage electrolytic capacitors generally have
lower ESR numbers, and for this reason it may be
necessary to select a capacitor rated for a higher voltage
than would normally be needed.
2. Output Capacitor Selection (C
OUT
)
A. C
OUT
= 680 µF to 2000 µF standard aluminum
electrolytic.
B.Capacitor voltage rating = 20V.
3. Catch Diode Selection (D1)
A.The catch-diode current rating must be at least 1.2
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 LM2576. 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.
3. Catch Diode Selection (D1)
A.For this example, a 3A current rating is adequate.
B. Use a 20V 1N5823 or SR302 Schottky diode, or any
of the suggested fast-recovery diodes shown in Figure 8.
4. Input Capacitor (C
IN
)
An aluminum or tantalum electrolytic bypass capacitor
located close to the regulator is needed for stable
operation.
4. Input Capacitor (C
IN
)
A 100 µF, 25V aluminum electrolytic capacitor located
near the input and ground pins provides sufficient
bypassing.
LM2576/LM2576HV
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