LM2576, LM2576HV
SNVS107F – JUNE 1999 – REVISED MAY 2021
LM2576xx Series SIMPLE SWITCHER® 3-A Step-Down Voltage Regulator
1 Features
•
•
•
•
•
•
•
•
•
•
•
Newer products available:
– LMR33630 36-V, 3-A, 400-kHz synchronous
converter
– LM76003 60-V, 3.5-A, 2.2-MHz synchronous
converter
3.3-V, 5-V, 12-V, 15-V, and adjustable output
versions
Adjustable version output voltage range,1.23 V to
37 V (57 V for HV version) ±4% maximum over line
and load conditions
Specified 3-A output current
Wide input voltage range: 40 V Up to 60 V for HV
version
Requires only four external components
52-kHz fixed-frequency internal oscillator
TTL-shutdown capability, low-power standby mode
High efficiency
Uses readily available standard inductors
Create a custom design using the LMR33630 or
LM76003 with the WEBENCH® Power Designer
2 Applications
•
•
•
•
Motor drives
Merchant network and server PSU
Appliances
Test and measurement equipment
Requiring a minimum number of external
components, these regulators are simple to use
and include fault protection 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 ±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.
The new product, LMR33630, offers reduced BOM
cost, higher efficiency, and an 85% reduction in
solution size among many other features. The
LM76003 requires very few external components and
has a pinout designed for simple, optimum PCB
layout for EMI and thermal performance. See the
device comparison table to compare specs.
Device Information
3 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 3-A load with excellent line and load
regulation. These devices are available in fixed output
voltages of 3.3 V, 5 V, 12 V, 15 V, and an adjustable
output version.
PART NUMBER(1)
LM2576
LM2576HV
(1)
PACKAGE
BODY SIZE (NOM)
TO-220 (5)
10.16 mm × 8.51 mm
DDPAK/TO-263 (5)
10.16 mm × 8.42 mm
For all available packages, see the orderable addendum at
the end of the data sheet.
Fixed Output Voltage Version Typical Application Diagram
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM2576, LM2576HV
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SNVS107F – JUNE 1999 – REVISED MAY 2021
Table of Contents
1 Features............................................................................1
2 Applications..................................................................... 1
3 Description.......................................................................1
4 Revision History.............................................................. 2
5 Pin Configuration and Functions...................................3
6 Specifications.................................................................. 4
6.1 Absolute Maximum Ratings........................................ 4
6.2 ESD Ratings............................................................... 4
6.3 Recommended Operating Conditions.........................4
6.4 Thermal Information....................................................4
6.5 Electrical Characteristics: 3.3 V.................................. 5
6.6 Electrical Characteristics: 5 V..................................... 5
6.7 Electrical Characteristics: 12 V................................... 5
6.8 Electrical Characteristics: 15 V................................... 6
6.9 Electrical Characteristics: Adjustable Output
Voltage.......................................................................... 6
6.10 Electrical Characteristics: All Output Voltage
Versions.........................................................................6
6.11 Typical Characteristics.............................................. 8
7 Detailed Description......................................................12
7.1 Overview................................................................... 12
7.2 Functional Block Diagram......................................... 12
7.3 Feature Description...................................................12
7.4 Device Functional Modes..........................................14
8 Application and Implementation.................................. 15
8.1 Application Information............................................. 15
8.2 Typical Applications.................................................. 19
9 Power Supply Recommendations................................25
10 Layout...........................................................................26
10.1 Layout Guidelines................................................... 26
10.2 Layout Example...................................................... 27
10.3 Grounding............................................................... 27
10.4 Heat Sink and Thermal Considerations.................. 27
11 Device and Documentation Support..........................29
11.1 Device Support........................................................29
11.2 Documentation Support.......................................... 30
11.3 Support Resources................................................. 30
11.4 Receiving Notification of Documentation Updates.. 30
11.5 Trademarks............................................................. 30
11.6 Electrostatic Discharge Caution.............................. 30
11.7 Glossary.................................................................. 30
12 Mechanical, Packaging, and Orderable
Information.................................................................... 30
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision E (June 2020) to Revision F (May 2021)
Page
• Added information for the LM76003 promotion.................................................................................................. 1
• Updated the numbering format for tables, figures, and cross-references throughout the document. ................1
Changes from Revision D (January 2016) to Revision E (June 2020)
Page
• Added information about the LMR33630............................................................................................................ 1
Changes from Revision C (April 2013) to Revision D (January 2016)
Page
• Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and
Implementation section, Power Supply Recommendations section, Layout section, Device and
Documentation Support section, and Mechanical, Packaging, and Orderable Information section................... 1
• Moved the thermal resistance data from the Electrical Characteristics: All Output Voltage Versions table to
the Thermal Information table.............................................................................................................................4
Changes from Revision B (April 2013) to Revision C (April 2013)
Page
• Changed layout of National Data Sheet to TI format.......................................................................................... 3
2
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5 Pin Configuration and Functions
Figure 5-1. KC Package 5-Pin TO-220 Top View
Figure 5-2. KTT Package 5-PIN DDPAK/TO-263 Top
View
Figure 5-3. DDPAK/TO-263 (S) Package 5-Lead
Surface-Mount Package Top View
Table 5-1. Pin Functions
PIN
NO.
NAME
I/O(1)
DESCRIPTION
1
VIN
I
Supply input pin to collector pin of high-side transistor. Connect to power supply and input
bypass capacitors CIN. Path from VIN pin to high frequency bypass CIN and GND must be as
short as possible.
2
OUTPUT
O
Emitter pin of the power transistor. This is a switching node. Attached this pin to an inductor
and the cathode of the external diode.
3
GROUND
—
Ground pin. Path to CIN must be as short as possible.
4
FEEDBACK
I
Feedback sense input pin. Connect to the midpoint of feedback divider to set VOUT for ADJ
version or connect this pin directly to the output capacitor for a fixed output version.
5
ON/OFF
I
Enable input to the voltage regulator. High = OFF and low = ON. Connect to GND to enable
the voltage regulator. Do not leave this pin float.
—
TAB
—
(1)
Connected to GND. Attached to heatsink for thermal relief for TO-220 package or put a
copper plane connected to this pin as a thermal relief for DDPAK package.
I = INPUT, O = OUTPUT
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6 Specifications
6.1 Absolute Maximum Ratings
over the recommended operating junction temperature range of -40°C to 125°C (unless otherwise noted)(1) (2)
MIN
Maximum supply voltage
45
LM2576HV
63
ON /OFF pin input voltage
Output voltage to ground
MAX
LM2576
(Steady-state)
Power dissipation
−0.3V ≤ V ≤ +VIN
V
−1
V
Maximum junction temperature, TJ
(2)
V
Internally Limited
Storage temperature, Tstg
(1)
UNIT
−65
150
°C
150
°C
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress
ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under
Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device
reliability.
If Military/Aerospace specified devices are required, please contact the TI Sales Office/ Distributors for availability and specifications.
6.2 ESD Ratings
V(ESD)
(1)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC
JS-001(1)
VALUE
UNIT
±2000
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over the recommended operating junction temperature range of -40°C to 125°C (unless otherwise noted)
Temperature
LM2576, LM2576HV
Supply voltage
MIN
MAX
UNIT
−40
125
°C
LM2576
40
LM2576HV
60
V
6.4 Thermal Information
LM2576, LM2576HV
THERMAL
KTT (TO-263)
KC (TO-220)
5 PINS
5 PINS
UNIT
RθJA
Junction-to-ambient thermal resistance
42.6
32.4
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
43.3
41.2
°C/W
RθJB
Junction-to-board thermal resistance
22.4
17.6
°C/W
ψJT
Junction-to-top characterization parameter
10.7
7.8
°C/W
ψJB
Junction-to-board characterization parameter
21.3
17
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
0.4
0.4
°C/W
(1)
(2)
(3)
4
METRIC(1) (2) (3)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953 and the Using New Thermal Metrics applications report, SBVA025.
The package thermal impedance is calculated in accordance with JESD 51-7
Thermal Resistances were simulated on a 4-layer, JEDEC board.
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6.5 Electrical Characteristics: 3.3 V
Specifications are for TJ = 25°C (unless otherwise noted).
PARAMETER
TEST CONDITIONS
SYSTEM PARAMETERS TEST CIRCUIT Figure 8-3 and Figure
(1)
TYP
MAX
UNIT
3.234
3.3
3.366
V
3.3
3.432
Output Voltage
VIN = 12 V, ILOAD = 0.5 A
Circuit of Figure 8-3 and Figure 8-9
TJ = 25°C
3.168
Output Voltage: LM2576
6 V ≤ VIN ≤ 40 V, 0.5 A ≤ ILOAD
≤3A
Circuit of Figure 8-3 and
Figure 8-9
Applies over full
operating temperature
range
3.135
TJ = 25°C
3.168
Output Voltage: LM2576HV
6 V ≤ VIN ≤ 60 V, 0.5 A ≤ ILOAD
≤3A
Circuit of Figure 8-3 and
Figure 8-9
Applies over full
operating temperature
range
3.135
Efficiency
VIN = 12 V, ILOAD = 3 A
VOUT
η
MIN
8-9(1)
3.465
3.3
V
3.45
3.482
V
75%
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 Figure 8-3 and Figure 8-9, system performance is as shown in Section 6.10.
6.6 Electrical Characteristics: 5 V
Specifications are for TJ = 25°C for the Figure 8-3 and Figure 8-9 (unless otherwise noted).
PARAMETER
TEST CONDITIONS
SYSTEM PARAMETERS TEST CIRCUIT Figure 8-3 and Figure
VOUT
Output Voltage
VIN = 12 V, ILOAD = 0.5 A
Circuit of Figure 8-3 and Figure 8-9
VOUT
0.5 A ≤ ILOAD ≤ 3 A,
8 V ≤ VIN ≤ 40 V
Circuit of Figure 8-3 and
Figure 8-9
TJ = 25°C
Output Voltage
LM2576
VOUT
0.5 A ≤ ILOAD ≤ 3 A,
8 V ≤ VIN ≤ 60 V
Circuit of Figure 8-3 and
Figure 8-9
TJ = 25°C
Output Voltage
LM2576HV
η
Efficiency
VIN = 12 V, ILOAD = 3 A
(1)
MIN
TYP
MAX
4.9
5
5.1
4.8
5
5.2
UNIT
8-9(1)
Applies over full
operating temperature
range
Applies over full
operating temperature
range
4.75
4.8
5.25
5
5.225
V
V
4.75
5.275
V
77%
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 Figure 8-3 and Figure 8-9, system performance is as shown in Section 6.10.
6.7 Electrical Characteristics: 12 V
Specifications are for TJ = 25°C (unless otherwise noted).
PARAMETER
TEST CONDITIONS
SYSTEM PARAMETERS TEST CIRCUIT Figure 8-3 and Figure
MIN
TYP
MAX
UNIT
11.76
12
12.24
V
11.52
12
12.48
8-9(1)
VOUT
Output Voltage
VIN = 25 V, ILOAD = 0.5 A
Circuit of Figure 8-3 and Figure 8-9
VOUT
0.5 A ≤ ILOAD ≤ 3 A,
15 V ≤ VIN ≤ 40 V
Circuit of Figure 8-3 and
Figure 8-9 and
TJ = 25°C
Output Voltage
LM2576
VOUT
0.5 A ≤ ILOAD ≤ 3 A,
15 V ≤ VIN ≤ 60 V
Circuit of Figure 8-3 and
Figure 8-9
TJ = 25°C
Output Voltage
LM2576HV
Applies over full
operating temperature
range
Applies over full
operating temperature
range
11.4
11.52
11.4
12.6
12
V
12.54
12.66
V
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Specifications are for TJ = 25°C (unless otherwise noted).
PARAMETER
η
(1)
Efficiency
TEST CONDITIONS
MIN
VIN = 15 V, ILOAD = 3 A
TYP
MAX
UNIT
88%
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 Figure 8-3 and Figure 8-9, system performance is as shown in Section 6.10.
6.8 Electrical Characteristics: 15 V
over operating free-air temperature range (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
14.7
15
15.3
V
14.4
15
15.6
SYSTEM PARAMETERS TEST CIRCUIT Figure 8-3 and Figure 8-9(1)
VOUT
Output Voltage
VIN = 25 V, ILOAD = 0.5 A
Circuit of Figure 8-3 and Figure 8-9
VOUT
0.5 A ≤ ILOAD ≤ 3 A,
18 V ≤ VIN ≤ 40 V
Circuit of Figure 8-3 and
Figure 8-9
TJ = 25°C
Output Voltage
LM2576
VOUT
0.5 A ≤ ILOAD ≤ 3 A,
18 V ≤ VIN ≤ 60 V
Circuit of Figure 8-3 and
Figure 8-9
TJ = 25°C
Output Voltage
LM2576HV
η
Efficiency
VIN = 18 V, ILOAD = 3 A
(1)
Applies over full
operating temperature
range
Applies over full
operating temperature
range
14.25
15.75
14.4
15
15.68
V
14.25
15.83
V
88%
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 Figure 8-3 and Figure 8-9, system performance is as shown in Section 6.10.
6.9 Electrical Characteristics: Adjustable Output Voltage
over operating free-air temperature range (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
1.217
1.23
1.243
V
1.193
1.23
1.267
SYSTEM PARAMETERS TEST CIRCUIT Figure 8-3 and Figure 8-9(1)
VOUT
Feedback voltage
VIN = 12 V, ILOAD = 0.5 A
VOUT = 5 V,
Circuit of Figure 8-3 and Figure 8-9
VOUT
0.5 A ≤ ILOAD ≤ 3 A,
8 V ≤ VIN ≤ 40 V
VOUT = 5 V, Circuit of Figure
8-3 and Figure 8-9
TJ = 25°C
Feedback Voltage
LM2576
VOUT
0.5 A ≤ ILOAD ≤ 3 A,
8 V ≤ VIN ≤ 60 V
VOUT = 5 V, Circuit of Figure
8-3 and Figure 8-9
TJ = 25°C
Feedback Voltage
LM2576HV
η
Efficiency
VIN = 12 V, ILOAD = 3 A, VOUT = 5 V
(1)
Applies over full
operating temperature
range
1.18
1.193
Applies over full
operating temperature
range
1.28
1.23
1.18
V
1.273
1.286
V
77%
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 Figure 8-3 and Figure 8-9, system performance is as shown in Section 6.10.
6.10 Electrical Characteristics: All Output Voltage Versions
over operating free-air temperature range (unless otherwise noted)
PARAMETER
TEST CONDITIONS
SYSTEM PARAMETERS TEST CIRCUIT Figure 8-3 and Figure
6
Ib
Feedback Bias Current
fO
Oscillator Frequency(7)
VOUT = 5 V (Adjustable
Version Only)
MIN
TYP(1)
MAX
UNIT
8-9(2)
TJ = 25°C
100
Applies over
full operating
temperature range
500
TJ = 25°C
47
Applies over full operating temperature range
42
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50
nA
52
58
63
kHz
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over operating free-air temperature range (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TJ = 25°C
VSAT
Saturation Voltage
DC
Max Duty Cycle (ON)(4)
ICL
Current Limit(3) (7)
IL
Output Leakage Current
IQ
Quiescent Current(5)
ISTBY
Standby Quiescent
Current
TYP(1)
1.4
Applies over
full operating
temperature range
IOUT = 3 A (3)
93%
98%
4.2
5.8
Applies over full operating temperature range
3.5
2
ON /OFF Pin = 5 V (OFF)
UNIT
1.8
2
TJ = 25°C
Output = 0 V
Output = −1 V
Output = −1 V (5) (6)
MAX
6.9
7.5
V
A
7.5
30
mA
5
10
mA
50
200
μA
ON /OFF CONTROL TEST CIRCUIT Figure 8-3 and Figure 8-9
VOUT = 0 V
VIH
ON /OFF Pin
Logic Input Level
VIL
IIH
IIL
(1)
(2)
(3)
(4)
(5)
(6)
(7)
ON /OFF Pin Input
Current
VOUT = Nominal Output
Voltage
TJ = 25°C
2.2
Applies over
full operating
temperature range
2.4
TJ = 25°C
1.4
V
1.2
Applies over
full operating
temperature range
1
0.8
V
ON /OFF Pin = 5 V (OFF)
12
30
μA
ON /OFF Pin = 0 V (ON)
0
10
μA
All limits specified at room temperature (25°C) unless otherwise noted. All room temperature limits are 100% production tested. All
limits at temperature extremes are specified through correlation using standard Statistical Quality Control (SQC) methods.
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 Figure 8-3 and Figure 8-9, system performance is as shown in Section 6.10.
Output pin sourcing current. No diode, inductor or capacitor connected to output.
Feedback pin removed from output and connected to 0V.
Feedback pin removed from output and connected to +12 V for the Adjustable, 3.3-V, and 5-V versions, and +25 V for the 12-V and
15-V versions, to force the output transistor OFF.
VIN = 40 V (60 V for high voltage version).
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%.
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6.11 Typical Characteristics
(Circuit of Figure 8-3 and Figure 8-9)
8
Figure 6-1. Normalized Output Voltage
Figure 6-2. Line Regulation
Figure 6-3. Dropout Voltage
Figure 6-4. Current Limit
Figure 6-5. Quiescent Current
Figure 6-6. Standby Quiescent Current
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Figure 6-7. Oscillator Frequency
Figure 6-9. Efficiency
Figure 6-11. Quiescent Current vs Duty Cycle
Figure 6-8. Switch Saturation Voltage
Figure 6-10. Minimum Operating Voltage
Figure 6-12. Feedback Voltage vs Duty Cycle
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Figure 6-13. Minimum Operating Voltage
Figure 6-14. Quiescent Current vs Duty Cycle
Figure 6-15. Feedback Voltage vs Duty Cycle
Figure 6-16. Feedback Pin Current
If the DDPAK/TO-263 package is used, the thermal resistance
can be reduced by increasing the PCB 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.
VOUT = 15 V A: Output Pin Voltage, 50 V/div B: Output
Pin Current, 2 A/div C: Inductor Current, 2 A/div D: Output
Ripple Voltage, 50 mV/div, AC-CoupledHorizontal Time Base:
5 μs/div
Figure 6-18. Switching Waveforms
Figure 6-17. Maximum Power Dissipation (DDPAK/
TO-263)
10
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Figure 6-19. Load Transient Response
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7 Detailed Description
7.1 Overview
The LM2576 SIMPLE SWITCHER® regulator is an easy-to-use, non-synchronous step-down DC-DC converter
with a wide input voltage range from 40 V to up to 60 V for a HV version. It is capable of delivering up to 3-A DC
load current with excellent line and load regulation. These devices are available in fixed output voltages of 3.3
V, 5 V, 12 V, 15 V, and an adjustable output version. The family requires few external components, and the pin
arrangement was designed for simple, optimum PCB layout.
7.2 Functional Block Diagram
VIN
Unregulated
DC Input
Internal
Rgulator
1
+
CIN
ON/OFF
ON/OFF
5
4
Feedback
R2
+
Fixed Gain
Error Amp
3 Amp
Switch
Comparator
+
R1
1k
±
Driver
±
OUTPUT
L1
2
D1
1.23 V
BAND-GAP
REFERENCE
52 kHZ
OSCILLATOR
RESET
THERMAL
SHUTDOWN
CURRENT
LIMIT
VOUT
+
COUT
3
L
O
A
D
GND
3.3 V R2 = 1.7 k 5 V, R2 = 3.1 k 12 V, R2 = 8.84 k 15 V, R2 = 11.3 k For ADJ. Version R1 = Open, R2 = 0 Ω Patent Pending
7.3 Feature Description
7.3.1 Undervoltage Lockout
In some applications it is desirable to keep the regulator off until the input voltage reaches a certain threshold.
Figure 7-1 shows an undervoltage lockout circuit that accomplishes this task, while Figure 7-2 shows the same
circuit applied to a buck-boost configuration. These circuits keep the regulator off until the input voltage reaches
a predetermined level.
VTH ≈ VZ1 + 2VBE(Q1)
12
(1)
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+VIN
+VIN
R1
20 k
LM2576-XX
1
+
CIN
20 k
5
ON/OFF
3
GND
Z1
Q1
R2
10 k
Complete circuit not shown.
Figure 7-1. Undervoltage Lockout for Buck Circuit
+VIN
+VIN
R1
20 k
LM2576-XX
1
+
CIN
20 k
5
ON/OFF
3
GND
Z1
Q1
R2
10 k
-VOUT
Complete circuit not shown (see Figure 8-1).
Figure 7-2. Undervoltage Lockout for Buck-Boost Circuit
7.3.2 Delayed Start-Up
The ON /OFF pin can be used to provide a delayed start-up feature as shown in Figure 7-3. With an input
voltage of 20 V and for the part values shown, the circuit provides approximately 10 ms of delay time before the
circuit begins switching. Increasing the RC time constant can provide longer delay 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.
7.3.3 Adjustable Output, Low-Ripple Power Supply
Figure 7-4 shows a 3-A power supply that features an adjustable output voltage. An additional LC filter that
reduces the output ripple by a factor of 10 or more is included in this circuit.
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+VIN
+VIN
+
CD
LM2576-XX
1
0.1 …F
+
CIN
5
ON/OFF
3
GND
100 …F
RD
47 K
Complete circuit not shown.
Figure 7-3. Delayed Start-Up
Feedback
55 V
Unregulated
DC Input
4
+VIN
LM2576HV-ADJ
1
+
CIN
Output
3
GND
100 …F
5
2
ON/OFF
Output
Voltage
L1
150 µH
+
D1
1N5822
COUT
R2
50 k
+1.2 to 50 V
@3A
20 µH
+
2000 …F
C1
100 …F
R1
1.21 k
optional output ripple filter
Figure 7-4. 1.2-V to 55-V Adjustable 3-A Power Supply With Low Output Ripple
7.4 Device Functional Modes
7.4.1 Shutdown Mode
The ON/OFF pin provides electrical ON and OFF control for the LM2576. When the voltage of this pin is higher
than 1.4 V, the device is in shutdown mode. The typical standby current in this mode is 50 μA.
7.4.2 Active Mode
When the voltage of the ON/OFF pin is below 1.2 V, the device starts switching, and the output voltage rises until
it reaches the normal regulation voltage.
7.4.3 Current Limit
The LM2576 device has current limiting to prevent the switch current from exceeding safe values during an
accidental overload on the output. This current limit value can be found in Section 6.10 under the heading of ICL.
The LM2576 uses cycle-by-cycle peak current limit for overload protection. This helps to prevent damage to the
device and external components. The regulator operates in current limit mode whenever the inductor current
exceeds the value of ICL given in Section 6.10. This occurs if the load current is greater than 3 A, or the
converter is starting up. Keep in mind that the maximum available load current depends on the input voltage,
output voltage, and inductor value. The regulator also incorporates short-circuit protection to prevent inductor
current run-away. When the voltage on the FB pin (ADJ) falls below about 0.58 V the switching frequency is
dropped to about 11 kHz. This allows the inductor current to ramp down sufficiently during the switch OFF-time
to prevent saturation.
14
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8 Application and Implementation
Note
Information in the following applications sections is not part of the TI component specification,
and TI does not warrant its accuracy or completeness. TI’s customers are responsible for
determining suitability of components for their purposes, as well as validating and testing their design
implementation to confirm system functionality.
8.1 Application Information
8.1.1 Input Capacitor (CIN)
To maintain stability, the regulator input pin must be bypassed with at least a 100-μF electrolytic capacitor. The
capacitor's leads must be kept short, and placed near the regulator.
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
temperatures and age. Paralleling a ceramic or solid tantalum capacitor increases the regulator stability at cold
temperatures. For maximum capacitor operating lifetime, the RMS ripple current rating of the capacitor must be
greater than:
(2)
8.1.2 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 performance and requirements.
The LM2576 (or any of the SIMPLE SWITCHER® family can be used for both continuous and discontinuous
modes of operation.
The inductor value selection guides in Figure 8-4 through Figure 8-8 are designed for buck regulator designs
of the continuous inductor current type. When using inductor values shown in the inductor selection guide, the
peak-to-peak inductor ripple current is 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 is 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.
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 possibility of discontinuous operation.
Inductors are available in different styles such as pot core, toriod, E-frame, bobbin core, and so on, as well as
different core materials, such as ferrites and powdered iron. The bobbin core is the least expensive type, and
consists of wire wrapped on a ferrite rod core. This type of construction makes for an inexpensive inductor;
however, because the magnetic flux is not completely contained within the core, the bobbin core generates
more electromagnetic interference (EMI). This EMI can cause problems in sensitive circuits, or can give incorrect
scope readings because of induced voltages in the scope probe.
The inductors listed in the selection chart include ferrite pot core construction for AIE, powdered iron toroid for
Pulse Engineering, and ferrite bobbin core for Renco.
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An inductor must not operate beyond its maximum-rated current because it may saturate. When an inductor
begins to saturate, the inductance decreases rapidly, and the inductor begins to look mainly resistive (the DC
resistance of the winding), causing the switch current to rise very rapidly. Different inductor types have different
saturation characteristics, and this must be considered when selecting an inductor.
The inductor manufacturer's data sheets include current and energy limits to avoid inductor saturation.
8.1.3 Inductor Ripple Current
When the switcher is operating in the continuous mode, the inductor current waveform ranges from a triangular
to a sawtooth 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 constant. 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).
If the load current drops to a low enough level, the bottom of the sawtooth current waveform reaches zero, and
the switcher changes 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) is forced to run discontinuous if the load
current is light enough.
8.1.4 Output Capacitor
An output capacitor is required to filter the output voltage and is needed for loop stability. The capacitor must be
placed near the LM2576 using short PCB traces. Standard aluminum electrolytics are usually adequate, but TI
recommends low ESR types for low output ripple voltage and good stability. The ESR of a capacitor depends on
many factors, including: the value, the voltage rating, physical size, and the type of construction. In general, low
value or low voltage (less than 12 V) 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 capacitor and the amplitude of the inductor ripple current (ΔIIND). See Section 8.1.3.
The lower capacitor values (220 μF to 1000 μF) allows typically 50 mV to 150 mV of output ripple voltage, while
larger-value capacitors reduces the ripple to approximately 20 mV to 50 mV.
Output Ripple Voltage = (ΔIIND) (ESR of COUT)
(3)
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 lowESR. These reduces the output ripple to 10 mV or 20 mV. However, when operating in the continuous mode,
reducing the ESR below 0.03 Ω can cause instability in the regulator.
Tantalum capacitors can have a very low ESR, and must be carefully evaluated if it is the only output capacitor.
Because of their good low temperature characteristics, a tantalum can be used in parallel with aluminum
electrolytics, with the tantalum making up 10% or 20% of the total capacitance.
The ripple current rating of the capacitor at 52 kHz should be at least 50% higher than the peak-to-peak inductor
ripple current.
8.1.5 Catch Diode
Buck regulators require a diode to provide a return path for the inductor current when the switch is off. This diode
must be placed close to the LM2576 using short leads and short printed-circuit traces.
Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best efficiency,
especially in low output voltage switching regulators (less than 5 V). Fast-recovery, high-efficiency, or ultra-fast
recovery diodes are also suitable, but some types with an abrupt turnoff characteristic may cause instability
and EMI problems. A fast-recovery diode with soft recovery characteristics is a better choice. Standard 60-Hz
diodes (for example, 1N4001 or 1N5400, and so on) are also not suitable. See Table 8-3 for Schottky and soft
fast-recovery diode selection guide.
16
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8.1.6 Output Voltage Ripple and Transients
The output voltage of a switching power supply contains 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.
The output ripple voltage is due mainly to the inductor sawtooth ripple current multiplied by the ESR of the output
capacitor (see Section 8.1.2).
The voltage spikes are present because of the fast switching action of the output switch, and the parasitic
inductance 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 evaluate these transients, all contribute to the amplitude of these spikes.
An additional small LC filter (20 μH and 100 μF) can be added to the output (as shown in Figure 7-4) to further
reduce the amount of output ripple and transients. A 10 × reduction in output ripple voltage and transients is
possible with this filter.
8.1.7 Feedback Connection
The LM2576 (fixed voltage versions) feedback pin must be wired to the output voltage point of the switching
power supply. 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.
8.1.8 ON /OFF INPUT
For normal operation, the ON /OFF pin must be grounded or driven with a low-level TTL voltage (typically
below 1.6 V). 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 must not be left
open.
8.1.9 Inverting Regulator
Figure 8-1 shows a LM2576-12 in a buck-boost configuration to generate a negative 12-V output from a positive
input voltage. This circuit bootstraps the ground pin of the regulator to the negative output voltage, then by
grounding the feedback pin, the regulator senses the inverted output voltage and regulates it to −12 V.
For an input voltage of 12 V 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 4.7 V.
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
5 A. Using a delayed turn-on or an undervoltage lockout circuit (described in Section 8.1.10) would allow the
input voltage to rise to a high enough level before the switcher would be allowed to turn on.
Because of the structural differences between the buck and the buck-boost regulator topologies, the buck
regulator design procedure section can not be used to select the inductor 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).
The peak inductor current, which is the same as the peak switch current, can be calculated in Equation 4:
(4)
where
•
fosc = 52 kHz
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Under normal continuous inductor current operating conditions, the minimum VIN represents the worst case.
Select an inductor that is rated for the peak current anticipated.
+12 To +45 V
Unregulated
DC Input
Feedback
4
+VIN
LM2576HV-ADJ
+
L1
Output
1
CIN
100 …F 3
GND
2
ON/OFF
5
68 µH
+
D1
1N5822
COUT
2200 …F
-12 @ 0.7 A
REGULATED
DC INPUT
Figure 8-1. Inverting Buck-Boost Develops −12 V
Also, the maximum voltage appearing across the regulator is the absolute sum of the input and output voltage.
For a −12-V output, the maximum input voltage for the LM2576 is +28 V, or +48 V for the LM2576HV.
8.1.10 Negative Boost Regulator
Another variation on the buck-boost topology is the negative boost configuration. The circuit in Figure 8-2
accepts an input voltage ranging from −5 V to −12 V and provides a regulated −12-V output. Input voltages
greater than −12 V causes the output to rise above −12 V, but does not damage the regulator.
+
Feedback
VIN
LM2576-12
1
4
Output
LOW ESR
2
+
3
GND
CIN
5
ON/OFF
COUT
2200 PF
1N5820
100 PF
VOUT = -12 V
100 PH
-VIN
-5 V to -12 V
Typical Load Current 400 mA for VIN = −5.2 V 750 mA for VIN = −7 V Heat sink may be required.
Figure 8-2. Negative Boost
Because of the boosting function of this type of regulator, the switch current is relatively high, especially at low
input voltages. Output load current limitations are a result of the maximum 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.
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8.2 Typical Applications
8.2.1 Fixed Output Voltage Version
Feedback
+VIN
LM2576HVFixed Output
4
Output
1
VIN
UNREGULATED
DC INPUT
2
+ 100 …F
GND
3
CIN
ON/OFF
VOUT
L1
100 µH
5
D1
MBR360
+
COUT
1000 µF
L
O
A
D
CIN — 100-μF, 75-V, Aluminum Electrolytic COUT — 1000-μF, 25-V, Aluminum Electrolytic D1 — Schottky, MBR360 L1 — 100 μH, Pulse
Eng. PE-92108 R1 — 2 k, 0.1% R2 — 6.12 k, 0.1%
Figure 8-3. Fixed Output Voltage Versions
8.2.1.1 Design Requirements
Table 8-1 lists the design parameters of this example.
Table 8-1. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Regulated Output Voltage
(3.3 V, 5 V, 12 V, or 15 V), VOUT
5V
Maximum Input Voltage, VIN(Max)
15 V
Maximum Load Current,
ILOAD(Max)
3A
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 Custom Design with WEBENCH Tools
Click here to create a custom design using the WEBENCH® Power Designer.
1. Start by entering your VIN, VOUT and IOUT requirements.
2. Optimize your design for key parameters like efficiency, footprint and cost using the optimizer dial and
compare this design with other possible solutions from Texas Instruments.
3. WEBENCH Power Designer provides you with a customized schematic along with a list of materials with real
time pricing and component availability.
4. In most cases, you will also be able to:
• Run electrical simulations to see important waveforms and circuit performance,
• Run thermal simulations to understand the thermal performance of your board,
• Export your customized schematic and layout into popular CAD formats,
• Print PDF reports for the design, and share your design with colleagues.
8.2.1.2.2 Inductor Selection (L1)
1. Select the correct Inductor value selection guide from Figure 8-4, Figure 8-5, Figure 8-6, or Figure 8-7.
(Output voltages of 3.3 V, 5 V, 12 V or 15 V respectively). For other output voltages, see the design
procedure for the adjustable version. Use the selection guide shown in Figure 8-5.
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2. From the inductor value selection guide, identify the inductance region intersected by VIN(Max) and
ILOAD(Max), and note the inductor code for that region. From the selection guide, the inductance area
intersected by the 15-V line and 3-A line is L100.
3. Identify the inductor value from the inductor code, and select an appropriate inductor from the table shown
in Figure 8-4. 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 × ILOAD. For
additional inductor information, see Section 8.1.2. Inductor value required is 100 μH from the table in Figure
8-4. Choose AIE 415-0930, Pulse Engineering PE92108, or Renco RL2444.
8.2.1.2.3 Output Capacitor Selection (COUT)
1. 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) TI recommends a value between 100 μF and 470 μF. We choose COUT = 680-μF to 2000-μF
standard aluminum electrolytic.
2. The voltage rating of the capacitor must be at least 1.5 times greater than the output voltage. For a 5-V
regulator, a rating of at least 8 V is appropriate, and a 10-V or 15-V rating is recommended. Capacitor
voltage rating = 20 V. 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.
8.2.1.2.4 Catch Diode Selection (D1)
1. 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. For this example, a 3-A current rating is adequate.
2. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. Use a 20-V
1N5823 or SR302 Schottky diode, or any of the suggested fast-recovery diodes shown in Table 8-3.
8.2.1.2.5 Input Capacitor (CIN)
An aluminum or tantalum electrolytic bypass capacitor located close to the regulator is needed for stable
operation. A 100-μF, 25-V aluminum electrolytic capacitor located near the input and ground pins provides
sufficient bypassing.
20
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8.2.1.3 Application Curves
Figure 8-4. LM2576(HV)-3.3
Figure 8-5. LM2576(HV)-5.0
Figure 8-6. LM2576(HV)-12
Figure 8-7. LM2576(HV)-15
Figure 8-8. LM2576(HV)-ADJ
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8.2.2 Adjusted Output Voltage Version
Feedback
+VIN
LM2576HVADJ
4
Output
1
7 V ± 60 V
UNREGULATED
DC INPUT
2
+ 100 …F
GND
CIN
3
ON/OFF
VOUT
5V
L1
100 µH
+
5
D1
MBR360
COUT
1000 µF
R2
R1
L
O
A
D
where VREF = 1.23 V, R1 between 1 k and 5 k
Figure 8-9. Adjustable Output Voltage Version
8.2.2.1 Design Requirements
Table 8-2 lists the design parameters of this example.
Table 8-2. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Regulated Output Voltage, VOUT
10 V
Maximum Input Voltage, VIN(Max)
25 V
Maximum Load Current,
ILOAD(Max)
3A
Switching Frequency, F
Fixed at 52 kHz
8.2.2.2 Detailed Design Procedure
8.2.2.2.1 Programming Output Voltage
Select R1 and R2, as shown in Figure 8-9.
Use Equation 5 to select the appropriate resistor values.
(5)
R1 can be between 1k and 5k. (For best temperature coefficient and stability with time, use 1% metal film
resistors)
(6)
(7)
R2 = 1 k (8.13 − 1) = 7.13 k, closest 1% value is 7.15 k
8.2.2.2.2 Inductor Selection (L1)
1. Calculate the inductor Volt • microsecond constant, E • T (V • μs), from Equation 8:
22
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VIN
V OUT
V OUT
VIN
u
1000
F in kHz
Vu V
(8)
Calculate E • T (V • μs)
EuT
25 10 u
10 1000
u
25
52
115 V u V
(9)
2. 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 8-8.
E • T = 115 V • μs
3. On the horizontal axis, select the maximum load current.
ILOAD(Max) = 3 A
4. Identify the inductance region intersected by the E • T value and the maximum load current value, and note
the inductor code for that region.
Inductance Region = H150
5. Identify the inductor value from the inductor code, and select an appropriate inductor from the table shown in
Table 8-4. 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 × ILOAD. For additional
inductor information, see Section 8.1.2.
Inductor Value = 150 μH
Choose from AIE part #415-0936, Pulse Engineering part #PE-531115, or Renco part #RL2445.
8.2.2.2.3 Output Capacitor Selection (COUT)
1. The value of the output capacitor together with the inductor defines the dominate pole-pair of the switching
regulator loop. For stable operation, the capacitor must satisfy Equation 10:
COUT t 13,300
VIN Max
V OUT u L
+
)
Equation 10 yields capacitor values between 10 μF and 2200 μF that satisfies 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 Equation 10
yields.
COUT t 13,300
25
10 u 150
22.2 )
However, for acceptable output ripple voltage select
COUT ≥ 680 μF
COUT = 680-μF electrolytic capacitor
2. The capacitor's voltage rating must be at last 1.5 times greater than the output voltage. For a 10-V regulator,
a rating of at least 15 V or more is recommended. Higher voltage electrolytic capacitors generally have lower
ESR numbers, and for this reason it may be necessary to select a capacitor rate for a higher voltage than
would normally be needed.
8.2.2.2.4 Catch Diode Selection (D1)
1. 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 must 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 Table 8-3. For this example, a 3.3-A current rating is adequate.
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2. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. Use a 30-V
31DQ03 Schottky diode, or any of the suggested fast-recovery diodes in Table 8-3.
8.2.2.2.5 Input Capacitor (CIN)
An aluminum or tantalum electrolytic bypass capacitor located close to the regulator is needed for stable
operation. A 100-μF aluminum electrolytic capacitor located near the input and ground pins provides sufficient
bypassing.
Table 8-3. Diode Selection Guide
SCHOTTKY
VR
3A
FAST RECOVERY
4 A to 6 A
3A
4 A to 6 A
The following
diodes are all
rated to 100-V
31DF1
HER302
The following
diodes are all
rated to 100-V
50WF10
MUR410
HER602
1N5820
20 V
MBR320P
1N5823
SR302
1N5821
MBR330
30 V
50WQ03
1N5824
31DQ03
SR303
1N5822
MBR340
50WQ04
1N5825
MBR340
40 V
31DQ04
SR304
MBR350
31DQ05
50 V
50WQ05
SR305
MBR360
50WR06
50SQ060
DQ06
60 V
SR306
Table 8-4. Inductor Selection by Manufacturer's Part Number
(1)
(2)
(3)
24
INDUCTOR CODE
INDUCTOR VALUE
SCHOTT(1)
PULSE ENG.(2)
RENCO(3)
L47
47 μH
671 26980
PE-53112
RL2442
L68
68 μH
671 26990
PE-92114
RL2443
L100
100 μH
671 27000
PE-92108
RL2444
L150
150 μH
671 27010
PE-53113
RL1954
L220
220 μH
671 27020
PE-52626
RL1953
L330
330 μH
671 27030
PE-52627
RL1952
L470
470 μH
671 27040
PE-53114
RL1951
L680
680 μH
671 27050
PE-52629
RL1950
H150
150 μH
671 27060
PE-53115
RL2445
H220
220 μH
671 27070
PE-53116
RL2446
H330
330 μH
671 27080
PE-53117
RL2447
H470
470 μH
671 27090
PE-53118
RL1961
H680
680 μH
671 27100
PE-53119
RL1960
H1000
1000 μH
671 27110
PE-53120
RL1959
H1500
1500 μH
671 27120
PE-53121
RL1958
H2200
2200 μH
671 27130
PE-53122
RL2448
Schott Corporation, (612) 475-1173, 1000 Parkers Lake Road, Wayzata, MN 55391.
Pulse Engineering, (619) 674-8100, P.O. Box 12235, San Diego, CA 92112.
Renco Electronics Incorporated, (516) 586-5566, 60 Jeffryn Blvd. East, Deer Park, NY 11729.
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9 Power Supply Recommendations
As in any switching regulator, layout is very important. Rapidly 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 construction should be used for best results. When using the adjustable version,
physically locate the programming resistors near the regulator, to keep the sensitive feedback wiring short.
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10 Layout
10.1 Layout Guidelines
Board layout is critical for the proper operation of switching power supplies. First, the ground plane area
must be sufficient for thermal dissipation purposes. Second, appropriate guidelines must be followed to reduce
the effects of switching noise. Switch mode converters are very fast switching devices. In such cases, the
rapid increase of input current combined with the parasitic trace inductance generates unwanted L di/dt noise
spikes. The magnitude of this noise tends to increase as the output current increases. This noise may turn into
electromagnetic interference (EMI) and can also cause problems in device performance. Therefore, take care in
layout to minimize the effect of this switching noise. The most important layout rule is to keep the AC current
loops as small as possible. Figure 10-1 shows the current flow in a buck converter. The top schematic shows
a dotted line which represents the current flow during the top-switch ON-state. The middle schematic shows
the current flow during the top-switch OFF-state. The bottom schematic shows the currents referred to as AC
currents. These AC currents are the most critical because they are changing in a very short time period. The
dotted lines of the bottom schematic are the traces to keep as short and wide as possible. This also yields a
small loop area reducing the loop inductance. To avoid functional problems due to layout, review the PCB layout
example. Best results are achieved if the placement of the LM2576 device, the bypass capacitor, the Schottky
diode, RFBB, RFBT, and the inductor are placed as shown in Figure 10-2.TI also recommends using 2-oz
copper boards or heavier to help thermal dissipation and to reduce the parasitic inductances of board traces.
See application note AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines (SNVA054) for more information.
Figure 10-1. Current Flow in Buck Application
26
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10.2 Layout Example
Figure 10-2. LM2576xx Layout Example
10.3 Grounding
To maintain output voltage stability, the power ground connections must be low-impedance (see Figure 8-3 and
Figure 8-9). For the 5-lead TO-220 and DDPAK/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.
10.4 Heat Sink and Thermal Considerations
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 is required, the following must be
identified:
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
temperature approximately 15°C cooler than the maximum temperatures must be selected.
4. LM2576 package thermal resistances θJA and θJC.
Total power dissipated by the LM2576 can be estimated in Equation 10:
PD = (VIN)(IQ) + (VO/VIN)(ILOAD)(VSAT)
(12)
where
•
•
IQ (quiescent current) and VSAT can be found in Section 6.11 shown previously,
VIN is the applied minimum input voltage, VO is the regulated output voltage,
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•
and ILOAD is the load current.
The dynamic losses during turnon and turnoff are negligible if a Schottky type catch diode is used.
When no heat sink is used, the junction temperature rise can be determined by Equation 11:
ΔTJ = (PD) (θJA)
(13)
To arrive at the actual operating junction temperature, add the junction temperature rise to the maximum ambient
temperature.
TJ = ΔTJ + TA
(14)
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 Equation 12:
ΔTJ = (PD) (θJC + θinterface + θHeat sink)
(15)
The operating junction temperature is:
TJ = TA + ΔTJ
(16)
As in Equation 14, if the actual operating junction temperature is greater than the selected safe operating
junction temperature, then a larger heat sink is required (one that has a lower thermal resistance).
28
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11 Device and Documentation Support
11.1 Device Support
11.1.1 Device Nomenclature
11.1.1.1 Definition of Terms
BUCK REGULATOR
A switching regulator topology in which a higher voltage is converted to a lower voltage.
Also known as a step-down switching regulator.
BUCK-BOOST
REGULATOR
A switching regulator topology in which a positive voltage is converted to a negative
voltage without a transformer.
DUTY CYCLE (D)
Ratio of the output switch's on-time to the oscillator period.
(17)
CATCH DIODE OR
The diode which provides a return path for the load current when the LM2576 switch is
CURRENT STEERING OFF.
DIODE
EFFICIENCY (η)
The proportion of input power actually delivered to the load.
(18)
CAPACITOR
EQUIVALENT
SERIES
RESISTANCE (ESR)
The purely resistive component of a real capacitor's impedance (see Figure 11-1). It
causes power loss resulting in capacitor heating, which directly affects the capacitor's
operating lifetime. When used as a switching regulator output filter, higher ESR values
result in higher output ripple voltages.
Figure 11-1. Simple Model of a Real Capacitor
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 lowinductance) in the 100 μF to 1000 μF range generally have ESR of less than 0.15Ω.
EQUIVALENT
SERIES
INDUCTANCE (ESL)
The pure inductance component of a capacitor (see Figure 11-1). The amount of
inductance is determined to a large extent on the capacitor's construction. In a buck
regulator, this unwanted inductance causes voltage spikes to appear on the output.
OUTPUT RIPPLE
VOLTAGE
The AC component of the switching regulator's output voltage. It is usually dominated
by the output capacitor's ESR multiplied by the inductor's ripple current (ΔIIND). The
peak-to-peak value of this sawtooth ripple current can be determined by reading
Section 8.1.3.
CAPACITOR RIPPLE RMS value of the maximum allowable alternating current at which a capacitor can be
CURRENT
operated continuously at a specified temperature.
STANDBY
QUIESCENT
CURRENT (ISTBY)
Supply current required by the LM2576 when in the standby mode ( ON /OFF pin is
driven to TTL-high voltage, thus turning the output switch OFF).
INDUCTOR RIPPLE
CURRENT (ΔIIND)
The peak-to-peak value of the inductor current waveform, typically a sawtooth
waveform when the regulator is operating in the continuous mode (vs. discontinuous
mode).
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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 inductor appears less inductive and the resistive
component dominates. Inductor current is then limited only by the DC resistance of
the wire and the available source current.
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 number of turns,
and the duty cycle.
11.1.2 Custom Design with WEBENCH Tools
Create a Custom Design with WEBENCH Tools
11.2 Documentation Support
11.2.1 Related Documentation
For related documentation, see the following:
AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines (SNVA054)
11.3 Support Resources
TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help — straight
from the experts. Search existing answers or ask your own question to get the quick design help you need.
Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do
not necessarily reflect TI's views; see TI's Terms of Use.
11.4 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. Click on
Subscribe to updates to register and receive a weekly digest of any product information that has changed. For
change details, review the revision history included in any revised document.
11.5 Trademarks
TI E2E™ is a trademark of Texas Instruments.
SIMPLE SWITCHER® is a registered trademark of TI.
WEBENCH® is a registered trademark of Texas Instruments.
is a registered trademark of Texas Instruments.
All trademarks are the property of their respective owners.
11.6 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled
with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may
be more susceptible to damage because very small parametric changes could cause the device not to meet its published
specifications.
11.7 Glossary
TI Glossary
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
30
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PACKAGE OPTION ADDENDUM
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PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
LM2576HVS-12
NRND
DDPAK/
TO-263
KTT
5
45
Non-RoHS
& Green
Call TI
Level-3-235C-168 HR
-40 to 125
LM2576
HVS-12 P+
LM2576HVS-12/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576
HVS-12 P+
Samples
LM2576HVS-3.3/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576
HVS-3.3 P+
Samples
LM2576HVS-5.0
NRND
DDPAK/
TO-263
KTT
5
45
Non-RoHS
& Green
Call TI
Level-3-235C-168 HR
-40 to 125
LM2576
HVS-5.0 P+
LM2576HVS-5.0/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576
HVS-5.0 P+
LM2576HVS-ADJ
NRND
DDPAK/
TO-263
KTT
5
45
Non-RoHS
& Green
Call TI
Level-3-235C-168 HR
-40 to 125
LM2576
HVS-ADJ P+
LM2576HVS-ADJ/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576
HVS-ADJ P+
LM2576HVSX-12
NRND
DDPAK/
TO-263
KTT
5
500
Non-RoHS
& Green
Call TI
Level-3-235C-168 HR
-40 to 125
LM2576
HVS-12 P+
LM2576HVSX-12/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
500
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576
HVS-12 P+
Samples
LM2576HVSX-3.3/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
500
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576
HVS-3.3 P+
Samples
LM2576HVSX-5.0
NRND
DDPAK/
TO-263
KTT
5
500
Non-RoHS
& Green
Call TI
Level-3-235C-168 HR
-40 to 125
LM2576
HVS-5.0 P+
LM2576HVSX-5.0/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
500
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576
HVS-5.0 P+
LM2576HVSX-ADJ
NRND
DDPAK/
TO-263
KTT
5
500
Non-RoHS
& Green
Call TI
Level-3-235C-168 HR
-40 to 125
LM2576
HVS-ADJ P+
LM2576HVSX-ADJ/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
500
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576
HVS-ADJ P+
LM2576HVT-12
NRND
TO-220
KC
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
-40 to 125
LM2576HVT
-12 P+
LM2576HVT-12/LF03
ACTIVE
TO-220
NDH
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576HVT-12/NOPB
ACTIVE
TO-220
KC
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
Addendum-Page 1
-40 to 125
Samples
Samples
Samples
Samples
LM2576HVT
-12 P+
Samples
LM2576HVT
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
13-May-2022
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
-12 P+
LM2576HVT-15/LB03
NRND
TO-220
NDH
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
LM2576HVT
-15 P+
LM2576HVT-15/LF03
ACTIVE
TO-220
NDH
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576HVT
-15 P+
Samples
LM2576HVT-15/NOPB
ACTIVE
TO-220
KC
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
-40 to 125
LM2576HVT
-15 P+
Samples
LM2576HVT-5.0
NRND
TO-220
KC
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
-40 to 125
LM2576HVT
-5.0 P+
LM2576HVT-5.0/LB03
NRND
TO-220
NDH
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
LM2576HVT
-5.0 P+
LM2576HVT-5.0/LF02
ACTIVE
TO-220
NEB
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576HVT
-5.0 P+
Samples
LM2576HVT-5.0/LF03
ACTIVE
TO-220
NDH
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576HVT
-5.0 P+
Samples
LM2576HVT-5.0/NOPB
ACTIVE
TO-220
KC
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
-40 to 125
LM2576HVT
-5.0 P+
Samples
LM2576HVT-ADJ
NRND
TO-220
KC
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
-40 to 125
LM2576HVT
-ADJ P+
LM2576HVT-ADJ/LB03
NRND
TO-220
NDH
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
LM2576HVT
-ADJ P+
LM2576HVT-ADJ/LF03
ACTIVE
TO-220
NDH
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576HVT
-ADJ P+
Samples
LM2576HVT-ADJ/NOPB
ACTIVE
TO-220
KC
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
-40 to 125
LM2576HVT
-ADJ P+
Samples
LM2576S-12
NRND
DDPAK/
TO-263
KTT
5
45
Non-RoHS
& Green
Call TI
Level-3-235C-168 HR
-40 to 125
LM2576S
-12 P+
LM2576S-12/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576S
-12 P+
Samples
LM2576S-3.3/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576S
-3.3 P+
Samples
LM2576S-5.0
NRND
DDPAK/
TO-263
KTT
5
45
Non-RoHS
& Green
Call TI
Level-3-235C-168 HR
-40 to 125
LM2576S
-5.0 P+
LM2576S-5.0/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576S
-5.0 P+
Addendum-Page 2
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
13-May-2022
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
LM2576S-ADJ/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
45
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576S
-ADJ P+
Samples
LM2576SX-3.3/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
500
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576S
-3.3 P+
Samples
LM2576SX-5.0/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
500
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576S
-5.0 P+
Samples
LM2576SX-ADJ/NOPB
ACTIVE
DDPAK/
TO-263
KTT
5
500
RoHS-Exempt
& Green
SN
Level-3-245C-168 HR
-40 to 125
LM2576S
-ADJ P+
Samples
LM2576T-12
NRND
TO-220
KC
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
-40 to 125
LM2576T
-12 P+
LM2576T-12/LB03
NRND
TO-220
NDH
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
LM2576T
-12 P+
LM2576T-12/LF03
ACTIVE
TO-220
NDH
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-12 P+
Samples
LM2576T-12/NOPB
ACTIVE
TO-220
KC
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-12 P+
Samples
LM2576T-15/LF03
ACTIVE
TO-220
NDH
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-15 P+
Samples
LM2576T-15/NOPB
ACTIVE
TO-220
KC
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-15 P+
Samples
LM2576T-3.3/LF03
ACTIVE
TO-220
NDH
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-3.3 P+
Samples
LM2576T-3.3/NOPB
ACTIVE
TO-220
KC
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
-40 to 125
LM2576T
-3.3 P+
Samples
LM2576T-5.0
NRND
TO-220
KC
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
-40 to 125
LM2576T
-5.0 P+
LM2576T-5.0/LB03
NRND
TO-220
NDH
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
LM2576T
-5.0 P+
LM2576T-5.0/LF02
ACTIVE
TO-220
NEB
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-5.0 P+
Samples
LM2576T-5.0/LF03
ACTIVE
TO-220
NDH
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-5.0 P+
Samples
LM2576T-5.0/NOPB
ACTIVE
TO-220
KC
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-5.0 P+
Samples
Addendum-Page 3
-40 to 125
-40 to 125
-40 to 125
PACKAGE OPTION ADDENDUM
www.ti.com
Orderable Device
13-May-2022
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
LM2576T-ADJ
NRND
TO-220
KC
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
-40 to 125
LM2576T-ADJ/LB03
NRND
TO-220
NDH
5
45
Non-RoHS
& Green
Call TI
Level-1-NA-UNLIM
LM2576T
-ADJ P+
LM2576T-ADJ/LF02
ACTIVE
TO-220
NEB
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-ADJ P+
Samples
LM2576T-ADJ/LF03
ACTIVE
TO-220
NDH
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-ADJ P+
Samples
LM2576T-ADJ/NOPB
ACTIVE
TO-220
KC
5
45
RoHS & Green
SN
Level-1-NA-UNLIM
LM2576T
-ADJ P+
Samples
-40 to 125
LM2576T
-ADJ P+
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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