LM2576-3.3MWC [NSC]
IC 7.5 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, UUC, WAFER, Switching Regulator or Controller;型号: | LM2576-3.3MWC |
厂家: | National Semiconductor |
描述: | IC 7.5 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, UUC, WAFER, Switching Regulator or Controller 开关 |
文件: | 总28页 (文件大小:750K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
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information and details on our current products and services.
June 1999
LM2576/LM2576HV Series
SIMPLE SWITCHER® 3A Step-Down Voltage Regulator
General Description
Features
n 3.3V, 5V, 12V, 15V, and adjustable output versions
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.
n Adjustable version output voltage range,
1.23V to 37V (57V for HV version) 4% max over
line and load conditions
n Guaranteed 3A output current
n Wide input voltage range, 40V up to 60V for
HV version
n Requires only 4 external components
n 52 kHz fixed frequency internal oscillator
n TTL shutdown capability, low power standby mode
n High efficiency
n Uses readily available standard inductors
n Thermal shutdown and current limit protection
n P+ Product Enhancement tested
±
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.
Applications
n Simple high-efficiency step-down (buck) regulator
n Efficient pre-regulator for linear regulators
n On-card switching regulators
±
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.
n Positive to negative converter (Buck-Boost)
Typical Application (Fixed Output Voltage Versions)
DS011476-1
FIGURE 1.
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation
DS011476
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Block Diagram
DS011476-2
=
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
Output Voltage
12
NS Package
Number
TS5B
Package
Range
Type
3.3
5.0
15
ADJ
−40˚C ≤ TA
≤ 125˚C
LM2576HVS-3.3
LM2576S-3.3
LM2576HVSX-3.3
LM2576SX-3.3
LM2576HVT-3.3
LM2576T-3.3
LM2576HVT-3.3
Flow LB03
LM2576HVS-5.0
LM2576S-5.0
LM2576HVSX-5.0
LM2576SX-5.0
LM2576HVT-5.0
LM2576T-5.0
LM2576HVT-5.0
Flow LB03
LM2576HVS-12
LM2576S-12
LM2576HVSX-12
LM2576SX-12
LM2576HVT-12
LM2576T-12
LM2576HVT-12
Flow LB03
LM2576HVS-15
LM2576S-15
LM2576HVSX-15
LM2576SX-15
LM2576HVT-15
LM2576T-15
LM2576HVT-15
Flow LB03
LM2576HVS-ADJ
LM2576S-ADJ
LM2576HVSX-ADJ
LM2576SX-ADJ
LM2576HVT-ADJ
LM2576T-ADJ
LM2576HVT-ADJ
Flow LB03
TO-263
TS5B
Tape & Reel
T05A
T05D
TO-220
LM2576T-3.3
Flow LB03
LM2576T-5.0
Flow LB03
LM2576T-12
Flow LB03
LM2576T-15
Flow LB03
LM2576T-ADJ
Flow LB03
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2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Minimum ESD Rating
=
=
(C 100 pF, R 1.5 kΩ)
Lead Temperature
2 kV
(Soldering, 10 Seconds)
260˚C
Maximum Supply Voltage
Operating Ratings
LM2576
45V
63V
LM2576HV
Temperature Range
LM2576/LM2576HV
Supply Voltage
LM2576
ON /OFF Pin Input Voltage
Output Voltage to Ground
(Steady State)
−0.3V ≤ V ≤ +VIN
−40˚C ≤ TJ ≤ +125˚C
−1V
Internally Limited
−65˚C to +150˚C
150˚C
40V
60V
Power Dissipation
LM2576HV
Storage Temperature Range
Maximum Junction Temperature
LM2576-3.3, LM2576HV-3.3
Electrical Characteristics
=
Specifications with standard type face are for TJ 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
3.3
3.3
3.3
75
Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
=
=
VOUT
VOUT
VOUT
η
Output Voltage
VIN 12V, ILOAD 0.5A
V
Circuit of Figure 2
3.234
3.366
V(Min)
V(Max)
V
Output Voltage
LM2576
6V ≤ VIN ≤ 40V, 0.5A ≤ ILOAD ≤ 3A
Circuit of Figure 2
3.168/3.135
3.432/3.465
V(Min)
V(Max)
V
Output Voltage
LM2576HV
6V ≤ VIN ≤ 60V, 0.5A ≤ ILOAD ≤ 3A
Circuit of Figure 2
3.168/3.135
3.450/3.482
V(Min)
V(Max)
%
= =
VIN 12V, ILOAD 3A
Efficiency
LM2576-5.0, LM2576HV-5.0
Electrical Characteristics
=
Specifications with standard type face are for TJ 25˚C, and those with Figure 2 boldface type apply over full Operating
Temperature Range.
Symbol
Parameter
Conditions
LM2576-5.0
Units
(Limits)
LM2576HV-5.0
Typ
5.0
5.0
5.0
77
Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
=
=
VOUT
VOUT
VOUT
η
Output Voltage
VIN 12V, ILOAD 0.5A
V
Circuit of Figure 2
4.900
5.100
V(Min)
V(Max)
V
Output Voltage
LM2576
0.5A ≤ ILOAD ≤ 3A,
8V ≤ VIN ≤ 40V
4.800/4.750
5.200/5.250
V(Min)
V(Max)
V
Circuit of Figure 2
0.5A ≤ ILOAD ≤ 3A,
8V ≤ VIN ≤ 60V
Output Voltage
LM2576HV
4.800/4.750
5.225/5.275
V(Min)
V(Max)
%
Circuit of Figure 2
= =
VIN 12V, ILOAD 3A
Efficiency
3
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LM2576-12, LM2576HV-12
Electrical Characteristics
=
Specifications with standard type face are for TJ 25˚C, and those with boldface type apply over full Operating Temperature
Range.
Symbol
Parameter
Conditions
LM2576-12
Units
(Limits)
LM2576HV-12
Typ
12
Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
=
=
VOUT
VOUT
VOUT
η
Output Voltage
VIN 25V, ILOAD 0.5A
V
Circuit of Figure 2
11.76
12.24
V(Min)
V(Max)
V
Output Voltage
LM2576
0.5A ≤ ILOAD ≤ 3A,
15V ≤ VIN ≤ 40V
Circuit of Figure 2
0.5A ≤ ILOAD ≤ 3A,
15V ≤ VIN ≤ 60V
Circuit of Figure 2
12
11.52/11.40
12.48/12.60
V(Min)
V(Max)
V
Output Voltage
LM2576HV
12
11.52/11.40
12.54/12.66
V(Min)
V(Max)
%
=
=
Efficiency
VIN 15V, ILOAD 3A
88
LM2576-15, LM2576HV-15
Electrical Characteristics
=
Specifications with standard type face are for TJ 25˚C, and those with boldface type apply over full Operating Temperature
Range.
Symbol
Parameter
Conditions
LM2576-15
Units
(Limits)
LM2576HV-15
Typ
15
Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
=
=
VOUT
VOUT
VOUT
η
Output Voltage
VIN 25V, ILOAD 0.5A
V
Circuit of Figure 2
14.70
15.30
V(Min)
V(Max)
V
Output Voltage
LM2576
0.5A ≤ ILOAD ≤ 3A,
18V ≤ VIN ≤ 40V
Circuit of Figure 2
0.5A ≤ ILOAD ≤ 3A,
18V ≤ VIN ≤ 60V
Circuit of Figure 2
15
14.40/14.25
15.60/15.75
V(Min)
V(Max)
V
Output Voltage
LM2576HV
15
14.40/14.25
15.68/15.83
V(Min)
V(Max)
%
=
=
Efficiency
VIN 18V, ILOAD 3A
88
LM2576-ADJ, LM2576HV-ADJ
Electrical Characteristics
=
Specifications with standard type face are for TJ 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
=
=
VOUT
Feedback Voltage
VIN 12V, ILOAD 0.5A
1.230
V
=
VOUT 5V,
1.217
1.243
V(Min)
V(Max)
Circuit of Figure 2
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4
LM2576-ADJ, LM2576HV-ADJ
Electrical Characteristics (Continued)
=
Specifications with standard type face are for TJ 25˚C, and those with boldface type apply over full Operating Temperature
Range.
Symbol
Parameter
Conditions
LM2576-ADJ
Units
(Limits)
LM2576HV-ADJ
Typ
1.230
1.230
77
Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
VOUT
VOUT
η
Feedback Voltage
LM2576
0.5A ≤ ILOAD ≤ 3A,
8V ≤ VIN ≤ 40V
V
1.193/1.180
1.267/1.280
V(Min)
V(Max)
V
=
VOUT 5V, Circuit of Figure 2
Feedback Voltage
LM2576HV
0.5A ≤ ILOAD ≤ 3A,
8V ≤ VIN ≤ 60V
1.193/1.180
1.273/1.286
V(Min)
V(Max)
%
=
VOUT 5V, Circuit of Figure 2
= = =
VIN 12V, ILOAD 3A, VOUT 5V
Efficiency
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 Temperature
=
=
Range. Unless otherwise specified, VIN 12V for the 3.3V, 5V, and Adjustable version, VIN 25V for the 12V version, and
=
=
VIN 30V for the 15V version. ILOAD 500 mA.
Symbol Parameter
Conditions
LM2576-XX
Units
(Limits)
LM2576HV-XX
Typ
Limit
(Note 2)
DEVICE PARAMETERS
=
Ib
Feedback Bias Current
VOUT 5V (Adjustable Version Only)
50
52
100/500
nA
fO
Oscillator Frequency
(Note 11)
kHz
47/42
58/63
kHz
(Min)
kHz
(Max)
=
VSAT
DC
Saturation Voltage
Max Duty Cycle (ON)
Current Limit
IOUT 3A (Note 4)
1.4
98
V
V(Max)
%
1.8/2.0
(Note 5)
93
%(Min)
A
ICL
(Notes 4, 11)
5.8
4.2/3.5
6.9/7.5
2
A(Min)
A(Max)
mA(Max)
mA
=
(Notes 6, 7): Output 0V
IL
Output Leakage Current
Quiescent Current
=
Output −1V
7.5
5
=
Output −1V
30
10
mA(Max)
mA
IQ
(Note 6)
mA(Max)
µA
=
ISTBY
Standby Quiescent
Current
ON /OFF Pin 5V (OFF)
50
200
µA(Max)
θJA
θJA
θJC
θJA
Thermal Resistance
T Package, Junction to Ambient (Note 8)
T Package, Junction to Ambient (Note 9)
T Package, Junction to Case
65
45
2
˚C/W
S Package, Junction to Ambient (Note 10)
50
5
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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 Temperature
=
=
Range. Unless otherwise specified, VIN 12V for the 3.3V, 5V, and Adjustable version, VIN 25V for the 12V version, and
=
=
VIN 30V for the 15V version. ILOAD 500 mA.
Symbol Parameter
Conditions
LM2576-XX
Units
(Limits)
LM2576HV-XX
Typ
Limit
(Note 2)
ON /OFF CONTROL Test Circuit Figure 2
=
VIH
VIL
IIH
ON /OFF Pin
Logic Input Level
ON /OFF Pin Input
Current
VOUT 0V
1.4
1.2
12
2.2/2.4
1.0/0.8
V(Min)
V(Max)
µA
=
VOUT Nominal Output Voltage
=
ON /OFF Pin 5V (OFF)
30
10
µA(Max)
µA
=
IIL
ON /OFF Pin 0V (ON)
0
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 in-
tended 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% produc-
tion 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.
=
40V (60V for high voltage version).
Note 7:
V
IN
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, θ is 50˚C/W, with 1 square inch of copper area, θ is 37˚C/W, and with 1.6 or more square inches of copper area, θ is 32˚C/W.
J
A
J
A
J
A
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
Dropout Voltage
DS011476-29
DS011476-27
DS011476-28
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6
Typical Performance Characteristics (Circuit of Figure 2) (Continued)
Current Limit
Quiescent Current
Standby
Quiescent Current
DS011476-30
DS011476-31
DS011476-32
Oscillator Frequency
Switch Saturation
Voltage
Efficiency
DS011476-35
DS011476-33
DS011476-34
Minimum Operating Voltage
Quiescent Current
vs Duty Cycle
Feedback Voltage
vs Duty Cycle
DS011476-36
DS011476-37
DS011476-38
7
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Typical Performance Characteristics (Circuit of Figure 2) (Continued)
Feedback Pin Current
Maximum Power Dissipation
(TO-263) (See Note 10)
DS011476-4
DS011476-24
Switching Waveforms
Load Transient Response
DS011476-5
DS011476-6
=
V
OUT
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
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8
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 Ad-
justable version, physically locate the programming resistors
near the regulator, to keep the sensitive feedback wiring
short.
Fixed Output Voltage Versions
DS011476-7
C
C
D
—
100 µF, 75V, Aluminum Electrolytic
1000 µF, 25V, Aluminum Electrolytic
Schottky, MBR360
IN
—
OUT
—
1
L
R
R
—
—
—
100 µH, Pulse Eng. PE-92108
2k, 0.1%
6.12k, 0.1%
1
1
2
Adjustable Output Voltage Version
DS011476-8
=
where V
REF
1.23V, R1 between 1k and 5k.
FIGURE 2.
9
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LM2576 Series Buck Regulator Design Procedure
PROCEDURE (Fixed Output Voltage Versions)
EXAMPLE (Fixed Output Voltage Versions)
Given:
Given:
=
=
VOUT 5V
VOUT Regulated Output Voltage
=
VIN(Max) 15V
(3.3V, 5V, 12V, or 15V)
=
=
VIN(Max) Maximum Input Voltage
ILOAD(Max) 3A
=
ILOAD(Max) Maximum Load Current
1. Inductor Selection (L1)
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.
A. Use the selection guide shown in Figure 4.
B. From the selection guide, the inductance area inter-
sected 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.
B. From the inductor value selection guide, identify the in-
ductance region intersected by VIN(Max) and ILOAD(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 manu-
facturers. The inductor chosen must be rated for opera-
tion at the LM2576 switching frequency (52 kHz) and for a
current rating of 1.15 x ILOAD. For additional inductor in-
formation, see the inductor section in the Application
Hints section of this data sheet.
2. Output Capacitor Selection (COUT
)
2. Output Capacitor Selection (COUT)
=
A. The value of the output capacitor together with the in-
ductor 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 recom-
mended.
A. COUT 680 µF to 2000 µF standard aluminum electro-
lytic.
=
B.Capacitor voltage rating 20V.
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 neces-
sary to select a capacitor rated for a higher voltage than
would normally be needed.
3. Catch Diode Selection (D1)
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.
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.
B. The reverse voltage rating of the diode should be at
least 1.25 times the maximum input voltage.
4. Input Capacitor (CIN
)
4. Input Capacitor (CIN)
An aluminum or tantalum electrolytic bypass capacitor lo-
cated close to the regulator is needed for stable opera-
tion.
A 100 µF, 25V aluminum electrolytic capacitor located
near the input and ground pins provides sufficient
bypassing.
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10
LM2576 Series Buck Regulator Design Procedure (Continued)
INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation)
DS011476-9
FIGURE 3. LM2576(HV)-3.3
DS011476-11
FIGURE 5. LM2576(HV)-12
DS011476-10
FIGURE 4. LM2576(HV)-5.0
DS011476-12
FIGURE 6. LM2576(HV)-15
11
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LM2576 Series Buck Regulator Design Procedure (Continued)
DS011476-13
FIGURE 7. LM2576(HV)-ADJ
PROCEDURE (Adjustable Output Voltage Versions)
Given:
EXAMPLE (Adjustable Output Voltage Versions)
Given:
=
=
VOUT 10V
VOUT Regulated Output Voltage
=
=
VIN(Max) 25V
VIN(Max) Maximum Input Voltage
=
=
ILOAD(Max) 3A
ILOAD(Max) Maximum Load Current
=
=
F
Switching Frequency (Fixed at 52 kHz)
F
52 kHz
1. Programming Output Voltage (Selecting R1 and R2,
1. Programming Output Voltage (Selecting R1 and R2)
as shown in Figure 2)
Use the following formula to select the appropriate resis-
tor values.
=
=
R2 1k (8.13 − 1) 7.13k, closest 1% value is 7.15k
R1 can be between 1k and 5k. (For best temperature co-
efficient and stability with time, use 1% metal film resis-
tors)
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12
LM2576 Series Buck Regulator Design Procedure (Continued)
PROCEDURE (Adjustable Output Voltage Versions)
EXAMPLE (Adjustable Output Voltage Versions)
2. Inductor Selection (L1)
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant,
A. Calculate E • T (V • µs)
E
•
T
(V
•
µs), from the following formula:
=
B. E • T 115 V • µs
B. Use the E • T value from the previous formula and
match it with the E • T number on the vertical axis of the
Inductor Value Selection Guide shown in Figure 7.
=
C. ILOAD(Max) 3A
D. Inductance Region H150
=
=
E. Inductor Value
#415-0936 Pulse Engineering part #PE-531115, or
Renco part #RL2445.
150 µH Choose from AIE part
C. On the horizontal axis, select the maximum load cur-
rent.
D. Identify the inductance region intersected by the E • T
value and the maximum load current value, and note the
inductor code for that region.
E. Identify the inductor value from the inductor code, and
select an appropriate inductor from the table shown in
Figure 9. Part numbers are listed for three inductor manu-
facturers. The inductor chosen must be rated for opera-
tion at the LM2576 switching frequency (52 kHz) and for a
current rating of 1.15 x ILOAD. For additional inductor in-
formation, see the inductor section in the application hints
section of this data sheet.
3. Output Capacitor Selection (COUT
)
3. Output Capacitor Selection (COUT
)
A. The value of the output capacitor together with the in-
ductor defines the dominate pole-pair of the switching
regulator loop. For stable operation, the capacitor must
satisfy the following requirement:
However, for acceptable output ripple voltage select
COUT ≥ 680 µF
=
COUT 680 µF electrolytic capacitor
The above formula yields capacitor values between 10 µF
and 2200 µF that will satisfy the loop requirements for
stable operation. But to achieve an acceptable output
ripple voltage, (approximately 1% of the output voltage)
and transient response, the output capacitor may need to
be several times larger than the above formula yields.
B. The capacitor’s voltage rating should be at last 1.5
times greater than the output voltage. For a 10V regulator,
a rating of at least 15V or more is recommended. Higher
voltage electrolytic capacitors generally have lower ESR
numbers, and for this reason it may be necessary to se-
lect a capacitor rate for a higher voltage than would nor-
mally be needed.
4. Catch Diode Selection (D1)
4. 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.
See diode selection guide in Figure 8.
A. For this example, a 3.3A current rating is adequate.
B. Use a 30V 31DQ03 Schottky diode, or any of the sug-
gested fast-recovery diodes in Figure 8.
B. The reverse voltage rating of the diode should be at
least 1.25 times the maximum input voltage.
5. Input Capacitor (CIN
)
5. Input Capacitor (CIN)
An aluminum or tantalum electrolytic bypass capacitor lo-
cated close to the regulator is needed for stable opera-
tion.
A 100 µF aluminum electrolytic capacitor located near the
input and ground pins provides sufficient bypassing.
13
www.national.com
LM2576 Series Buck Regulator Design Procedure (Continued)
To further simplify the buck regulator design procedure, National Semiconductor is making available computer design software to
be used with the SIMPLE SWITCHER line of switching regulators. Switchers Made Simple (Version 3.3) is available on a (31⁄
")
2
diskette for IBM compatible computers from a National Semiconductor sales office in your area.
VR
Schottky
Fast Recovery
4A–6A
3A
1N5820
MBR320P
SR302
4A–6A
1N5823
3A
20V
30V
40V
1N5821
MBR330
31DQ03
SR303
50WQ03
1N5824
The following
diodes are all
rated to 100V
The following
diodes are all
rated to 100V
1N5822
MBR340
31DQ04
SR304
MBR340
50WQ04
1N5825
50WF10
MUR410
HER602
31DF1
HER302
50V
60V
MBR350
31DQ05
SR305
50WQ05
MBR360
DQ06
50WR06
50SQ060
SR306
FIGURE 8. Diode Selection Guide
Inductor
Code
Inductor
Value
Schott
Pulse Eng.
(Note 13)
PE-53112
PE-92114
PE-92108
PE-53113
PE-52626
PE-52627
PE-53114
PE-52629
PE-53115
PE-53116
PE-53117
PE-53118
PE-53119
PE-53120
PE-53121
PE-53122
Renco
(Note 14)
RL2442
RL2443
RL2444
RL1954
RL1953
RL1952
RL1951
RL1950
RL2445
RL2446
RL2447
RL1961
RL1960
RL1959
RL1958
RL2448
(Note 12)
L47
47 µH
671 26980
671 26990
671 27000
671 27010
671 27020
671 27030
671 27040
671 27050
671 27060
671 27070
671 27080
671 27090
671 27100
671 27110
671 27120
671 27130
L68
68 µH
100 µH
150 µH
220 µH
330 µH
470 µH
680 µH
150 µH
220 µH
330 µH
470 µH
680 µH
L100
L150
L220
L330
L470
L680
H150
H220
H330
H470
H680
H1000
H1500
H2200
1000 µH
1500 µH
2200 µH
Note 12: Schott Corporation, (612) 475-1173, 1000 Parkers Lake Road, Wayzata, MN 55391.
Note 13: Pulse Engineering, (619) 674-8100, P.O. Box 12235, San Diego, CA 92112.
Note 14: Renco Electronics Incorporated, (516) 586-5566, 60 Jeffryn Blvd. East, Deer Park, NY 11729.
FIGURE 9. Inductor Selection by Manufacturer’s Part Number
www.national.com
14
Application Hints
INPUT CAPACITOR (CIN
)
magnetic interference (EMI). This EMI can cause problems
in sensitive circuits, or can give incorrect scope readings be-
cause of induced voltages in the scope probe.
To maintain stability, the regulator input pin must be by-
passed with at least a 100 µF electrolytic capacitor. The ca-
pacitor’s leads must be kept short, and located near the
regulator.
The inductors listed in the selection chart include ferrite pot
core construction for AIE, powdered iron toroid for Pulse En-
gineering, and ferrite bobbin core for Renco.
If the operating temperature range includes temperatures
below −25˚C, the input capacitor value may need to be
larger. With most electrolytic capacitors, the capacitance
value decreases and the ESR increases with lower tempera-
tures and age. Paralleling a ceramic or solid tantalum ca-
pacitor will increase the regulator stability at cold tempera-
tures. For maximum capacitor operating lifetime, the
capacitor’s RMS ripple current rating should be greater than
An inductor should not be operated beyond its maximum
rated current because it may saturate. When an inductor be-
gins to saturate, the inductance decreases rapidly and the
inductor begins to look mainly resistive (the DC resistance of
the winding). This will cause the switch current to rise very
rapidly. Different inductor types have different saturation
characteristics, and this should be kept in mind when select-
ing an inductor.
The inductor manufacturer’s data sheets include current and
energy limits to avoid inductor saturation.
INDUCTOR RIPPLE CURRENT
When the switcher is operating in the continuous mode, the
inductor current waveform ranges from a triangular to a saw-
tooth type of waveform (depending on the input voltage). For
a given input voltage and output voltage, the peak-to-peak
amplitude of this inductor current waveform remains con-
stant. As the load current rises or falls, the entire sawtooth
current waveform also rises or falls. The average DC value
of this waveform is equal to the DC load current (in the buck
regulator configuration).
INDUCTOR SELECTION
All switching regulators have two basic modes of operation:
continuous and discontinuous. The difference between the
two types relates to the inductor current, whether it is flowing
continuously, or if it drops to zero for a period of time in the
normal switching cycle. Each mode has distinctively different
operating characteristics, which can affect the regulator per-
formance and requirements.
If the load current drops to a low enough level, the bottom of
the sawtooth current waveform will reach zero, and the
switcher will change to a discontinuous mode of operation.
This is a perfectly acceptable mode of operation. Any buck
switching regulator (no matter how large the inductor value
is) will be forced to run discontinuous if the load current is
light enough.
The LM2576 (or any of the SIMPLE SWITCHER family) can
be used for both continuous and discontinuous modes of op-
eration.
OUTPUT CAPACITOR
The inductor value selection guides in Figure 3 through Fig-
ure 7 were designed for buck regulator designs of the con-
tinuous inductor current type. When using inductor values
shown in the inductor selection guide, the peak-to-peak in-
ductor ripple current will be approximately 20% to 30% of the
maximum DC current. With relatively heavy load currents,
the circuit operates in the continuous mode (inductor current
always flowing), but under light load conditions, the circuit
will be forced to the discontinuous mode (inductor current
falls to zero for a period of time). This discontinuous mode of
operation is perfectly acceptable. For light loads (less than
approximately 300 mA) it may be desirable to operate the
regulator in the discontinuous mode, primarily because of
the lower inductor values required for the discontinuous
mode.
An output capacitor is required to filter the output voltage and
is needed for loop stability. The capacitor should be located
near the LM2576 using short pc board traces. Standard alu-
minum electrolytics are usually adequate, but low ESR types
are recommended for low output ripple voltage and good
stability. The ESR of a capacitor depends on many factors,
some which are: the value, the voltage rating, physical size
and the type of construction. In general, low value or low
voltage (less than 12V) electrolytic capacitors usually have
higher ESR numbers.
The amount of output ripple voltage is primarily a function of
the ESR (Equivalent Series Resistance) of the output ca-
pacitor and the amplitude of the inductor ripple current
(∆IIND). See the section on inductor ripple current in Applica-
tion Hints.
The selection guide chooses inductor values suitable for
continuous mode operation, but if the inductor value chosen
is prohibitively high, the designer should investigate the pos-
sibility of discontinuous operation. The computer design soft-
ware Switchers Made Simple will provide all component
values for discontinuous (as well as continuous) mode of op-
eration.
The lower capacitor values (220 µF–1000 µF) will allow typi-
cally 50 mV to 150 mV of output ripple voltage, while
larger-value capacitors will reduce the ripple to approxi-
mately 20 mV to 50 mV.
=
Output Ripple Voltage (∆IIND) (ESR of COUT
)
To further reduce the output ripple voltage, several standard
electrolytic capacitors may be paralleled, or a higher-grade
capacitor may be used. Such capacitors are often called
“high-frequency,” “low-inductance,” or “low-ESR.” These will
reduce the output ripple to 10 mV or 20 mV. However, when
operating in the continuous mode, reducing the ESR below
0.03Ω can cause instability in the regulator.
Inductors are available in different styles such as pot core,
toriod, E-frame, bobbin core, etc., as well as different core
materials, such as ferrites and powdered iron. The least ex-
pensive, the bobbin core type, consists of wire wrapped on a
ferrite rod core. This type of construction makes for an inex-
pensive inductor, but since the magnetic flux is not com-
pletely contained within the core, it generates more electro-
15
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GROUNDING
Application Hints (Continued)
To maintain output voltage stability, the power ground con-
nections must be low-impedance (see Figure 2). For the
5-lead TO-220 and TO-263 style package, both the tab and
pin 3 are ground and either connection may be used, as they
are both part of the same copper lead frame.
Tantalum capacitors can have a very low ESR, and should
be carefully evaluated if it is the only output capacitor. Be-
cause of their good low temperature characteristics, a tanta-
lum can be used in parallel with aluminum electrolytics, with
the tantalum making up 10% or 20% of the total capacitance.
HEAT SINK/THERMAL CONSIDERATIONS
The capacitor’s ripple current rating at 52 kHz should be at
least 50% higher than the peak-to-peak inductor ripple cur-
rent.
In many cases, only a small heat sink is required to keep the
LM2576 junction temperature within the allowed operating
range. For each application, to determine whether or not a
heat sink will be required, the following must be identified:
CATCH DIODE
Buck regulators require a diode to provide a return path for
the inductor current when the switch is off. This diode should
be located close to the LM2576 using short leads and short
printed circuit traces.
1. Maximum ambient temperature (in the application).
2. Maximum regulator power dissipation (in application).
3. Maximum allowed junction temperature (125˚C for the
LM2576). For a safe, conservative design, a tempera-
ture approximately 15˚C cooler than the maximum tem-
peratures should be selected.
Because of their fast switching speed and low forward volt-
age drop, Schottky diodes provide the best efficiency, espe-
cially in low output voltage switching regulators (less than
5V). Fast-Recovery, High-Efficiency, or Ultra-Fast Recovery
diodes are also suitable, but some types with an abrupt
turn-off characteristic may cause instability and EMI prob-
lems. A fast-recovery diode with soft recovery characteristics
is a better choice. Standard 60 Hz diodes (e.g., 1N4001 or
1N5400, etc.) are also not suitable. See Figure 8 for Schot-
tky and “soft” fast-recovery diode selection guide.
4. LM2576 package thermal resistances θJA and θJC
.
Total power dissipated by the LM2576 can be estimated as
follows:
=
PD (VIN)(IQ) + (VO/VIN)(ILOAD)(VSAT
)
where IQ (quiescent current) and VSAT can be found in the
Characteristic Curves shown previously, VIN is the applied
minimum input voltage, VO is the regulated output voltage,
and ILOAD is the load current. The dynamic losses during
turn-on and turn-off are negligible if a Schottky type catch di-
ode is used.
OUTPUT VOLTAGE RIPPLE AND TRANSIENTS
The output voltage of a switching power supply will contain a
sawtooth ripple voltage at the switcher frequency, typically
about 1% of the output voltage, and may also contain short
voltage spikes at the peaks of the sawtooth waveform.
When no heat sink is used, the junction temperature rise can
be determined by the following:
=
∆TJ (PD) (θJA
)
The output ripple voltage is due mainly to the inductor saw-
tooth ripple current multiplied by the ESR of the output ca-
pacitor. (See the inductor selection in the application hints.)
To arrive at the actual operating junction temperature, add
the junction temperature rise to the maximum ambient tem-
perature.
The voltage spikes are present because of the the fast
switching action of the output switch, and the parasitic induc-
tance of the output filter capacitor. To minimize these voltage
spikes, special low inductance capacitors can be used, and
their lead lengths must be kept short. Wiring inductance,
stray capacitance, as well as the scope probe used to evalu-
ate these transients, all contribute to the amplitude of these
spikes.
=
TJ ∆TJ + TA
If the actual operating junction temperature is greater than
the selected safe operating junction temperature determined
in step 3, then a heat sink is required.
When using a heat sink, the junction temperature rise can be
determined by the following:
=
∆TJ (PD) (θJC + θinterface + θHeat sink
)
An additional small LC filter (20 µH & 100 µF) can be added
to the output (as shown in Figure 15) to further reduce the
amount of output ripple and transients. A 10 x reduction in
output ripple voltage and transients is possible with this filter.
The operating junction temperature will be:
=
TJ TA + ∆TJ
As above, if the actual operating junction temperature is
greater than the selected safe operating junction tempera-
ture, then a larger heat sink is required (one that has a lower
thermal resistance).
FEEDBACK CONNECTION
The LM2576 (fixed voltage versions) feedback pin must be
wired to the output voltage point of the switching power sup-
ply. When using the adjustable version, physically locate
both output voltage programming resistors near the LM2576
to avoid picking up unwanted noise. Avoid using resistors
greater than 100 kΩ because of the increased chance of
noise pickup.
Included on the Switcher Made Simple design software is a
more precise (non-linear) thermal model that can be used to
determine junction temperature with different input-output
parameters or different component values. It can also calcu-
late the heat sink thermal resistance required to maintain the
regulators junction temperature below the maximum operat-
ing temperature.
ON /OFF INPUT
For normal operation, the ON /OFF pin should be grounded
or driven with a low-level TTL voltage (typically below 1.6V).
To put the regulator into standby mode, drive this pin with a
high-level TTL or CMOS signal. The ON /OFF pin can be
safely pulled up to +VIN without a resistor in series with it.
The ON /OFF pin should not be left open.
Additional Applications
INVERTING REGULATOR
Figure 10 shows a LM2576-12 in a buck-boost configuration
to generate a negative 12V output from a positive input volt-
age. This circuit bootstraps the regulator’s ground pin to the
www.national.com
16
Additional Applications (Continued)
negative output voltage, then by grounding the feedback pin,
the regulator senses the inverted output voltage and regu-
lates it to −12V.
For an input voltage of 12V or more, the maximum available
output current in this configuration is approximately 700 mA.
At lighter loads, the minimum input voltage required drops to
approximately 4.7V.
The switch currents in this buck-boost configuration are
higher than in the standard buck-mode design, thus lowering
the available output current. Also, the start-up input current
of the buck-boost converter is higher than the standard
buck-mode regulator, and this may overload an input power
source with a current limit less than 5A. Using a delayed
turn-on or an undervoltage lockout circuit (described in the
next section) would allow the input voltage to rise to a high
enough level before the switcher would be allowed to turn
on.
DS011476-15
Typical Load Current
=
=
400 mA for V
750 mA for V
−5.2V
−7V
IN
IN
Note: Heat sink may be required.
FIGURE 11. Negative Boost
Because of the boosting function of this type of regulator, the
switch current is relatively high, especially at low input volt-
ages. Output load current limitations are a result of the maxi-
mum current rating of the switch. Also, boost regulators can
not provide current limiting load protection in the event of a
shorted load, so some other means (such as a fuse) may be
necessary.
Because of the structural differences between the buck and
the buck-boost regulator topologies, the buck regulator de-
sign procedure section can not be used to to select the in-
ductor or the output capacitor. The recommended range of
inductor values for the buck-boost design is between 68 µH
and 220 µH, and the output capacitor values must be larger
than what is normally required for buck designs. Low input
voltages or high output currents require a large value output
capacitor (in the thousands of micro Farads).
UNDERVOLTAGE LOCKOUT
In some applications it is desirable to keep the regulator off
until the input voltage reaches a certain threshold. An under-
voltage lockout circuit which accomplishes this task is shown
in Figure 12, while Figure 13 shows the same circuit applied
to a buck-boost configuration. These circuits keep the regu-
lator off until the input voltage reaches a predetermined
level.
The peak inductor current, which is the same as the peak
switch current, can be calculated from the following formula:
=
Where fosc 52 kHz. Under normal continuous inductor cur-
VTH ≈ VZ1 + 2VBE(Q1)
rent operating conditions, the minimum VIN represents the
worst case. Select an inductor that is rated for the peak cur-
rent anticipated.
DS011476-14
FIGURE 10. Inverting Buck-Boost Develops −12V
DS011476-16
Note: Complete circuit not shown.
Also, the maximum voltage appearing across the regulator is
the absolute sum of the input and output voltage. For a −12V
output, the maximum input voltage for the LM2576 is +28V,
or +48V for the LM2576HV.
FIGURE 12. Undervoltage Lockout for Buck Circuit
The Switchers Made Simple (version 3.0) design software
can be used to determine the feasibility of regulator designs
using different topologies, different input-output parameters,
different components, etc.
NEGATIVE BOOST REGULATOR
Another variation on the buck-boost topology is the negative
boost configuration. The circuit in Figure 11 accepts an input
voltage ranging from −5V to −12V and provides a regulated
−12V output. Input voltages greater than −12V will cause the
output to rise above −12V, but will not damage the regulator.
17
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ing. Increasing the RC time constant can provide longer de-
lay times. But excessively large RC time constants can
cause problems with input voltages that are high in 60 Hz or
120 Hz ripple, by coupling the ripple into the ON /OFF pin.
Additional Applications (Continued)
ADJUSTABLE OUTPUT, LOW-RIPPLE POWER SUPPLY
A 3A power supply that features an adjustable output voltage
is shown in Figure 15. An additional L-C filter that reduces
the output ripple by a factor of 10 or more is included in this
circuit.
DS011476-17
Note: Complete circuit not shown (see Figure 10).
FIGURE 13. Undervoltage Lockout
for Buck-Boost Circuit
DELAYED STARTUP
DS011476-18
The ON /OFF pin can be used to provide a delayed startup
feature as shown in Figure 14. With an input voltage of 20V
and for the part values shown, the circuit provides approxi-
mately 10 ms of delay time before the circuit begins switch-
Note: Complete circuit not shown.
FIGURE 14. Delayed Startup
DS011476-19
FIGURE 15. 1.2V to 55V Adjustable 3A Power Supply with Low Output Ripple
CATCH DIODE OR CURRENT STEERING DIODE
Definition of Terms
The diode which provides a return path for the load current
when the LM2576 switch is OFF.
BUCK REGULATOR
EFFICIENCY (η)
A switching regulator topology in which a higher voltage is
converted to a lower voltage. Also known as a step-down
switching regulator.
The proportion of input power actually delivered to the load.
BUCK-BOOST REGULATOR
A switching regulator topology in which a positive voltage is
converted to a negative voltage without a transformer.
CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)
The purely resistive component of a real capacitor’s imped-
ance (see Figure 16). It causes power loss resulting in ca-
pacitor heating, which directly affects the capacitor’s operat-
ing lifetime. When used as a switching regulator output filter,
higher ESR values result in higher output ripple voltages.
DUTY CYCLE (D)
Ratio of the output switch’s on-time to the oscillator period.
DS011476-20
FIGURE 16. Simple Model of a Real Capacitor
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18
Definition of Terms (Continued)
Connection Diagrams (Note 15)
Most standard aluminum electrolytic capacitors in the
100 µF–1000 µF range have 0.5Ω to 0.1Ω ESR.
Higher-grade capacitors (“low-ESR”, “high-frequency”, or
“low-inductance”) in the 100 µF–1000 µF range generally
have ESR of less than 0.15Ω.
Straight Leads
5-Lead TO-220 (T)
Top View
EQUIVALENT SERIES INDUCTANCE (ESL)
The pure inductance component of a capacitor (see Figure
16). The amount of inductance is determined to a large ex-
tent on the capacitor’s construction. In a buck regulator, this
unwanted inductance causes voltage spikes to appear on
the output.
DS011476-21
LM2576T-XX or LM2576HVT-XX
NS Package Number T05A
TO-263 (S)
5-Lead Surface-Mount Package
Top View
OUTPUT RIPPLE VOLTAGE
The AC component of the switching regulator’s output volt-
age. It is usually dominated by the output capacitor’s ESR
multiplied by the inductor’s ripple current (∆IIND). The
peak-to-peak value of this sawtooth ripple current can be de-
termined by reading the Inductor Ripple Current section of
the Application hints.
CAPACITOR RIPPLE CURRENT
RMS value of the maximum allowable alternating current at
which a capacitor can be operated continuously at a speci-
fied temperature.
DS011476-25
STANDBY QUIESCENT CURRENT (ISTBY
)
LM2576S-XX or LM2576HVS-XX
NS Package Number TS5B
LM2576SX-XX or LM2576HVSX-XX
NS Package Number TS5B, Tape and Reel
Supply current required by the LM2576 when in the standby
mode (ON /OFF pin is driven to TTL-high voltage, thus turn-
ing the output switch OFF).
INDUCTOR RIPPLE CURRENT (∆IIND
)
The peak-to-peak value of the inductor current waveform,
typically a sawtooth waveform when the regulator is operat-
ing in the continuous mode (vs. discontinuous mode).
Bent, Staggered Leads
5-Lead TO-220 (T)
Top View
CONTINUOUS/DISCONTINUOUS MODE OPERATION
Relates to the inductor current. In the continuous mode, the
inductor current is always flowing and never drops to zero,
vs. the discontinuous mode, where the inductor current
drops to zero for a period of time in the normal switching
cycle.
INDUCTOR SATURATION
The condition which exists when an inductor cannot hold any
more magnetic flux. When an inductor saturates, the induc-
tor appears less inductive and the resistive component domi-
nates. Inductor current is then limited only by the DC resis-
tance of the wire and the available source current.
DS011476-22
LM2576T-XX Flow LB03
or LM2576HVT-XX Flow LB03
NS Package Number T05D
OPERATING VOLT MICROSECOND CONSTANT (E•Top
)
The product (in VoIt•µs) of the voltage applied to the inductor
and the time the voltage is applied. This E•Top constant is a
measure of the energy handling capability of an inductor and
is dependent upon the type of core, the core area, the num-
ber of turns, and the duty cycle.
Note 15: (XX indicates output voltage option. See ordering information table
for complete part number.)
19
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Physical Dimensions inches (millimeters) unless otherwise noted
5-Lead TO-220 (T)
Order Number LM2576T-3.3, LM2576HVT-3.3,
LM2576T-5.0, LM2576HVT-5.0, LM2576T-12,
LM2576HVT-12, LM2576T-15, LM2576HVT-15,
LM2576T-ADJ or LM2576HVT-ADJ
NS Package Number T05A
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20
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Bent, Staggered 5-Lead TO-220 (T)
Order Number LM2576T-3.3 Flow LB03, LM2576T-XX Flow LB03, LM2576HVT-3.3 Flow LB03,
LM2576T-5.0 Flow LB03, LM2576HVT-5.0 Flow LB03,
LM2576T-12 Flow LB03, LM2576HVT-12 Flow LB03,
LM2576T-15 Flow LB03, LM2576HVT-15 Flow LB03,
LM2576T-ADJ Flow LB03 or LM2576HVT-ADJ Flow LB03
NS Package Number T05D
21
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
5-Lead TO-263 (S)
Order Number LM2576S-3.3, LM2576S-5.0,
LM2576S-12,LM2576S-15, LM2576S-ADJ,
LM2576HVS-3.3, LM2576HVS-5.0, LM2576HVS-12,
LM2576HVS-15, or LM2576HVS-ADJ
NS Package Number TS5B
5-Lead TO-263 in Tape & Reel (SX)
Order Number LM2576SX-3.3, LM2576SX-5.0,
LM2576SX-12, LM2576SX-15, LM2576SX-ADJ,
LM2576HVSX-3.3, LM2576HVSX-5.0, LM2576HVSX-12,
LM2576HVSX-15, or LM2576HVSX-ADJ
NS Package Number TS5B
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Products > Analog - Regulators > Simple Switchers > LM2576
LM2576 Product Folder
SIMPLE SWITCHER 3A Step-Down Voltage Regulator
LM2596 - low cost & more efficient
See Also:
LM2599 - improved switching frequency, and efficiency.
LM2673 - much improved switching frequency
LM2676 - more improved efficiency and switching frequency.
Generic P/N 2576
General
Package
& Models
Samples
& Pricing
Design
Tools
Application
Notes
Features
Datasheet
Description
WEBENCH Live Simulation!
Parametric Table
Multiple Output Capability
On/Off Pin
No
Yes
No
4
LM2576 Webench™ Custom
Design/Analyze/Build It
Error Flag
V in Lower
11.0
V in Upper
Input Voltage, min (Volt)
Input Voltage, max (Volt)
Output Current, max
Output Voltage (Volt)
Adjustable Output Voltage
Switching Frequency (Hz)
Adjustable Switching Frequency
Sync Pin
6.0 <=
V out
I out
<=
13.0
<= 40.0
<= 37.0
<= 3.00
<= 100
V
V
40, 60
3000 mA
1.2 <=
3.3
V
12, 15, 3.30, 5, 1.20
2.50
A
No, Yes
52000
No
Ambient Temperature
30
°C
No
Create This Design
Efficiency (%)
88, 75, 77
No
What is Webench?
Flyback
Inverting
Yes
Step-up
No
Step-down
Yes
-
Datasheet
Size in
Kbytes
Title
Date
Receive via
Email
Download
View Online
29-
Jun-
99
Receive via
Email
LM2576 LM2576HV Series SIMPLE SWITCHER 3A Step-
Down Voltage Regulator
639
Kbytes
View Online Download
LM2576 LM2576HV Series SIMPLE SWITCHER 3A Step-
Down Voltage Regulator (JAPANESE)
869
Kbytes
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Package Availability, Models, Samples & Pricing
Budgetary
Pricing
Package
Type Pins MSL
TO
Models
Samples &
Electronic
Orders
Std
Pack
Size
Package
Marking
Part
Number
Status
$US
each
SPICE IBIS
Qty
rail [logo]¢U¢Z¢2¢T
of
45
Full
production
MSL
LM2576T-12
LM2576T-15
5
N/A
N/A
N/A
N/A
1K+ $1.3600
LM2576T
-12 P+
Buy Now
24 Hour
220
rail [logo]¢U¢Z¢2¢T
of
45
TO
220
MSL
5
Full production
Full production
Full production
Full production
1K+ $1.3600
1K+ $1.3600
1K+ $1.3600
1K+ $1.3600
LM2576T
-15 P+
Buy Now
24 Hour
rail [logo]¢U¢Z¢2¢T
of
45
TO
220
MSL
MSL
MSL
LM2576T-3.3
LM2576T-5.0
LM2576T-ADJ
5
5
5
N/A
N/A
N/A
N/A
N/A
N/A
LM2576T
-3.3 P+
Buy Now
24 Hour
rail [logo]¢U¢Z¢2¢T
of
45
TO
220
LM2576T
-5.0 P+
Buy Now
24 Hour
rail [logo]¢U¢Z¢2¢T
of
45
TO
220
LM2576T
-ADJ P+
Buy Now
24 Hour
rail [logo]¢U¢Z¢2¢T
TO
263
MSL
MSL
MSL
MSL
LM2576S-12
LM2576S-15
LM2576S-3.3
LM2576S-5.0
5
5
5
5
Full production
Full production
Full production
Full production
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
1K+ $1.3600
1K+ $1.3600
1K+ $1.3600
1K+ $1.3600
of
45
LM2576S
-12 P+
Buy Now
24 Hour
rail [logo]¢U¢Z¢2¢T
TO
263
of
45
LM2576S
-15 P+
Buy Now
24 Hour
rail [logo]¢U¢Z¢2¢T
TO
263
of
45
LM2576S
-3.3 P+
Buy Now
24 Hour
rail [logo]¢U¢Z¢2¢T
TO
263
of
45
LM2576S
-5.0 P+
Buy Now
24 Hour
rail [logo]¢U¢Z¢2¢T
TO
263
LM2576S-
ADJ
MSL
MSL
5
5
Full production
Full production
N/A
N/A
N/A
N/A
1K+ $1.3600
1K+ $1.3600
of
45
LM2576S
-ADJ P+
Buy Now
reel [logo]¢U¢Z¢2¢T
TO
263
LM2576SX-
12
of
500
LM2576S
-12 P+
reel [logo]¢U¢Z¢2¢T
TO
263
LM2576SX-
15
MSL
MSL
MSL
MSL
5
5
Full production
Full production
Full production
Full production
Full production
Full production
Full production
Full production
Full production
Full production
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
1K+ $1.3600
1K+ $1.3600
1K+ $1.3600
1K+ $1.3600
of
500
LM2576S
-15 P+
reel [logo]¢U¢Z¢2¢T
TO
263
LM2576SX-
3.3
of
500
LM2576S
-3.3 P+
Buy Now
Buy Now
reel [logo]¢U¢Z¢2¢T
TO
263
LM2576SX-
5.0
5
of
500
LM2576S
-5.0 P+
reel [logo]¢U¢Z¢2¢T
TO
263
LM2576SX-
ADJ
5
of
500
LM2576S
-ADJ P+
Buy Now
Samples
tray
of
N/A
LM2576-12
MDC
Die
Die
Die
Die
Die
Die
-
-
-
-
-
-
tray
of
N/A
LM2576-15
MDC
Samples
Samples
Samples
Samples
Samples
tray
of
N/A
LM2576-3.3
MDC
tray
of
N/A
LM2576-5.0
MDC
tray
of
N/A
LM2576-ADJ
MDC
tray
of
LM2576HV-5
MDC
N/A
wafer
jar
of
LM2576-12
MWC
Wafer
Wafer
Wafer
Wafer
Wafer
Wafer
Full production
Full production
Full production
Full production
Full production
Full production
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
-
-
-
-
-
-
N/A
wafer
jar
of
LM2576-15
MWC
N/A
wafer
jar
of
LM2576-3.3
MWC
N/A
wafer
jar
of
LM2576-5.0
MWC
N/A
wafer
jar
of
LM2576-ADJ
MWC
N/A
wafer
jar
of
LM2576HV-5
MWC
N/A
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 available 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 reduces 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 output voltage within specified input voltages and
output load conditions, and ±10% on the oscillator frequency. External shutdown is included, featuring 50 µA
(typical) standby current. The output switch includes cycle-by-cycle current limiting, as well as thermal
shutdown for full protection under fault conditions.
Features
●
●
3.3V, 5V, 12V, 15V, and adjustable output versions
Adjustable version output voltage range, 1.23V to 37V (57V for HV version) ±4% max over line and
load conditions
●
●
●
●
●
●
●
●
●
Guaranteed 3A output current
Wide input voltage range, 40V up to 60V for HV version
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
P+ Product Enhancement tested
Applications
●
●
●
●
Simple high-efficiency step-down (buck) regulator
Efficient pre-regulator for linear regulators
On-card switching regulators
Positive to negative converter (Buck-Boost)
Design Tools
Title
Size in Kbytes Date
Receive via
Email
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SimpleSwitcher® DC-DC
Converters Design Software
12-Jun-
2002
View
10 Kbytes
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Application Notes
Size in
Kbytes
Title
Date
Receive via
Email
Download
View Online
5-
Jan-
97
Receive via
Email
AN-1061: AN-1061 Power Conversion in Line-Powered
Equipment
142
Kbytes
View Online Download
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29-
Jul-
02
Receive via
Email
AN-1229: Application Note 1229 SIMPLE SWITCHER PCB 229
Layout Guidelines
Kbytes
1-
May-
98
Receive via
Email
AN-776: Application Note 776 20 Watt Simple Switcher 387
Forward Converter
Kbytes
5-
Aug-
95
Receive via
Email
AN-946: High-Efficiency 3A Battery Chargers Use
LM2576 Regulators
109
Kbytes
High-Efficiency 3A Battery Chargers Use LM2576
Regulators (JAPANESE)
72
Kbytes
View Online Download
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[Information as of 5-Aug-2002]
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