LM2576, LM2576HV
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LM2576/LM2576HV Series SIMPLE SWITCHER
®
3A Step-Down Voltage Regulator
Check for Samples: LM2576,LM2576HV
1FEATURES DESCRIPTION
The LM2576 series of regulators are monolithic
23• 3.3V, 5V, 12V, 15V, and Adjustable Output integrated circuits that provide all the active functions
Versions for a step-down (buck) switching regulator, capable of
• Adjustable Version Output Voltage driving 3A load with excellent line and load regulation.
Range,1.23V to 37V (57V for HV Version) ±4% These devices are available in fixed output voltages
Max Over Line and Load Conditions of 3.3V, 5V, 12V, 15V, and an adjustable output
version.
• Specified 3A Output Current
• Wide Input Voltage Range, 40V Up to 60V for Requiring a minimum number of external
HV Version components, these regulators are simple to use and
include internal frequency compensation and a fixed-
• Requires Only 4 External Components frequency oscillator.
• 52 kHz Fixed Frequency Internal Oscillator The LM2576 series offers a high-efficiency
• TTL Shutdown Capability, Low Power Standby replacement for popular three-terminal linear
Mode regulators. It substantially reduces the size of the
• High Efficiency heat sink, and in some cases no heat sink is
required.
• Uses Readily Available Standard Inductors
• Thermal Shutdown and Current Limit A standard series of inductors optimized for use with
Protection the LM2576 are available from several different
manufacturers. This feature greatly simplifies the
• P+ Product Enhancement Tested design of switch-mode power supplies.
APPLICATIONS Other features include a specified ±4% tolerance on
output voltage within specified input voltages and
• Simple High-Efficiency Step-Down (Buck) output load conditions, and ±10% on the oscillator
Regulator frequency. External shutdown is included, featuring
• Efficient Pre-Regulator for Linear Regulators 50 μA (typical) standby current. The output switch
includes cycle-by-cycle current limiting, as well as
• On-Card Switching Regulators thermal shutdown for full protection under fault
• Positive to Negative Converter (Buck-Boost) conditions.
TYPICAL APPLICATION
(Fixed Output Voltage Versions)
Figure 1.
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2SIMPLE SWITCHER is a registered trademark of Texas Instruments.
3All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 1999–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
LM2576, LM2576HV
SNVS107C –JUNE 1999–REVISED APRIL 2013
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Block Diagram
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
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
ABSOLUTE MAXIMUM RATINGS (1)(2)
Maximum Supply Voltage LM2576 45V
LM2576HV 63V
ON /OFF Pin Input Voltage −0.3V ≤V≤+VIN
Output Voltage to Ground (Steady State) −1V
Power Dissipation Internally Limited
Storage Temperature Range −65°C to +150°C
Maximum Junction Temperature 150°C
Minimum ESD Rating (C = 100 pF, R = 1.5 kΩ) 2 kV
Lead Temperature (Soldering, 10 Seconds) 260°C
(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional, but do not ensured specific performance limits. For ensured specifications and test
conditions, see ELECTRICAL CHARACTERISTICS ALL OUTPUT VOLTAGE VERSIONS.
(2) If Military/Aerospace specified devices are required, please contact the TI Sales Office/ Distributors for availability and specifications.
OPERATING RATINGS
Temperature Range LM2576/LM2576HV −40°C ≤TJ≤+125°C
Supply Voltage LM2576 40V
LM2576HV 60V
ELECTRICAL CHARACTERISTICS LM2576-3.3, LM2576HV-3.3
Specifications with standard type face are for TJ= 25°C, and those with boldface type apply over full Operating Temperature
Range. LM2576-3.3 Units
LM2576HV-3.3
Symbol Parameter Conditions (Limits)
Typ Limit (1)
SYSTEM PARAMETERS Test Circuit Figure 21 and Figure 22(2)
VOUT Output Voltage VIN = 12V, ILOAD = 0.5A 3.3 V
Circuit of Figure 21 and Figure 22 3.234 V(Min)
3.366 V(Max)
VOUT Output Voltage 6V ≤VIN ≤40V, 0.5A ≤ILOAD ≤3A 3.3 V
LM2576 Circuit of Figure 21 and Figure 22 3.168/3.135 V(Min)
3.432/3.465 V(Max)
VOUT Output Voltage 6V ≤VIN ≤60V, 0.5A ≤ILOAD ≤3A 3.3 V
LM2576HV Circuit of Figure 21 and Figure 22 3.168/3.135 V(Min)
3.450/3.482 V(Max)
ηEfficiency VIN = 12V, ILOAD = 3A 75 %
(1) All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits
are 100% production tested. All limits at temperature extremes are specified via correlation using standard Statistical Quality Control
(SQC) methods.
(2) 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 21 and Figure 22, system performance will be as shown in ELECTRICAL
CHARACTERISTICS ALL OUTPUT VOLTAGE VERSIONS.
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ELECTRICAL CHARACTERISTICS LM2576-5.0, LM2576HV-5.0
Specifications with standard type face are for TJ= 25°C, and those with Figure 21 and Figure 22 boldface type apply over
full Operating Temperature Range. LM2576-5.0 Units
LM2576HV-5.0
Symbol Parameter Conditions (Limits)
Typ Limit (1)
SYSTEM PARAMETERS Figure 21 and Figure 22(2)
VOUT Output Voltage VIN = 12V, ILOAD = 0.5A 5.0 V
Circuit of Figure 21 and Figure 22 4.900 V(Min)
5.100 V(Max)
VOUT Output Voltage 0.5A ≤ILOAD ≤3A, 5.0 V
LM2576 8V ≤VIN ≤40V 4.800/4.750 V(Min)
Circuit of Figure 21 and Figure 22 5.200/5.250 V(Max)
VOUT Output Voltage 0.5A ≤ILOAD ≤3A, 5.0 V
LM2576HV 8V ≤VIN ≤60V 4.800/4.750 V(Min)
Circuit of Figure 21 and Figure 22 5.225/5.275 V(Max)
ηEfficiency VIN = 12V, ILOAD = 3A 77 %
(1) All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits
are 100% production tested. All limits at temperature extremes are specified via correlation using standard Statistical Quality Control
(SQC) methods.
(2) 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 21 and Figure 22, system performance will be as shown in ELECTRICAL
CHARACTERISTICS ALL OUTPUT VOLTAGE VERSIONS.
ELECTRICAL CHARACTERISTICS LM2576-12, LM2576HV-12
Specifications with standard type face are for TJ= 25°C, and those with boldface type apply over full Operating Temperature
Range. LM2576-12 Units
LM2576HV-12
Symbol Parameter Conditions (Limits)
Typ Limit (1)
SYSTEM PARAMETERS Test Circuit Figure 21 and Figure 22(2)
VOUT Output Voltage VIN = 25V, ILOAD = 0.5A 12 V
Circuit of Figure 21 and Figure 22 V(Min)
11.76
12.24 V(Max)
VOUT Output Voltage 0.5A ≤ILOAD ≤3A, 12 V
LM2576 15V ≤VIN ≤40V V(Min)
11.52/11.40
Circuit of Figure 21 and Figure 22 and 12.48/12.60 V(Max)
VOUT Output Voltage 0.5A ≤ILOAD ≤3A, 12 V
LM2576HV 15V ≤VIN ≤60V V(Min)
11.52/11.40
Circuit of Figure 21 and Figure 22 12.54/12.66 V(Max)
ηEfficiency VIN = 15V, ILOAD = 3A 88 %
(1) All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits
are 100% production tested. All limits at temperature extremes are specified via correlation using standard Statistical Quality Control
(SQC) methods.
(2) 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 21 and Figure 22, system performance will be as shown in ELECTRICAL
CHARACTERISTICS ALL OUTPUT VOLTAGE VERSIONS.
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ELECTRICAL CHARACTERISTICS LM2576-15, LM2576HV-15
Specifications with standard type face are for TJ= 25°C, and those with boldface type apply over full Operating Temperature
Range. LM2576-15 Units
LM2576HV-15
Symbol Parameter Conditions (Limits)
Typ Limit (1)
SYSTEM PARAMETERS Test Circuit Figure 21 and Figure 22(2)
VOUT Output Voltage VIN = 25V, ILOAD = 0.5A 15 V
Circuit of Figure 21 and Figure 22 14.70 V(Min)
15.30 V(Max)
VOUT Output Voltage 0.5A ≤ILOAD ≤3A, 15 V
LM2576 18V ≤VIN ≤40V 14.40/14.25 V(Min)
Circuit of Figure 21 and Figure 22 15.60/15.75 V(Max)
VOUT Output Voltage 0.5A ≤ILOAD ≤3A, 15 V
LM2576HV 18V ≤VIN ≤60V 14.40/14.25 V(Min)
Circuit of Figure 21 and Figure 22 15.68/15.83 V(Max)
ηEfficiency VIN = 18V, ILOAD = 3A 88 %
(1) All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits
are 100% production tested. All limits at temperature extremes are specified via correlation using standard Statistical Quality Control
(SQC) methods.
(2) 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 21 and Figure 22, system performance will be as shown in ELECTRICAL
CHARACTERISTICS ALL OUTPUT VOLTAGE VERSIONS.
ELECTRICAL CHARACTERISTICS LM2576-ADJ, LM2576HV-ADJ
Specifications with standard type face are for TJ= 25°C, and those with boldface type apply over full Operating Temperature
Range. LM2576-ADJ Units
LM2576HV-ADJ
Symbol Parameter Conditions (Limits)
Typ Limit (1)
SYSTEM PARAMETERS Test Circuit Figure 21 and Figure 22(2)
VOUT Feedback Voltage VIN = 12V, ILOAD = 0.5A 1.230 V
VOUT = 5V, 1.217 V(Min)
Circuit of Figure 21 and Figure 22 1.243 V(Max)
VOUT Feedback Voltage 0.5A ≤ILOAD ≤3A, 1.230 V
LM2576 8V ≤VIN ≤40V 1.193/1.180 V(Min)
VOUT = 5V, Circuit of Figure 21 and Figure 22 1.267/1.280 V(Max)
VOUT Feedback Voltage 0.5A ≤ILOAD ≤3A, 1.230 V
LM2576HV 8V ≤VIN ≤60V 1.193/1.180 V(Min)
VOUT = 5V, Circuit of Figure 21 and Figure 22 1.273/1.286 V(Max)
ηEfficiency VIN = 12V, ILOAD = 3A, VOUT = 5V 77 %
(1) All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits
are 100% production tested. All limits at temperature extremes are specified via correlation using standard Statistical Quality Control
(SQC) methods.
(2) 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 21 and Figure 22, system performance will be as shown in ELECTRICAL
CHARACTERISTICS ALL OUTPUT VOLTAGE VERSIONS.
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ELECTRICAL CHARACTERISTICS ALL OUTPUT VOLTAGE VERSIONS
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. LM2576-XX Units
LM2576HV-XX
Symbol Parameter Conditions (Limits)
Typ Limit (1)
DEVICE PARAMETERS
IbFeedback Bias Current VOUT = 5V (Adjustable Version Only) 50 100/500 nA
fOOscillator Frequency See (2) 52 kHz
47/42 kHz (Min)
58/63 kHz (Max)
VSAT Saturation Voltage IOUT = 3A (3) 1.4 V
1.8/2.0 V(Max)
DC Max Duty Cycle (ON) See (4) 98 %
93 %(Min)
ICL Current Limit See (3)(2) 5.8 A
4.2/3.5 A(Min)
6.9/7.5 A(Max)
ILOutput Leakage Current Output = 0V 2 mA(Max)
Output = −1V 7.5 mA
Output = −1V (5)(6) 30 mA(Max)
IQQuiescent Current See (5) 5 mA
10 mA(Max)
ISTBY Standby Quiescent ON /OFF Pin = 5V (OFF) 50 μA
Current 200 μA(Max)
θJA Thermal Resistance T Package, Junction to Ambient (7) 65
θJA T Package, Junction to Ambient (8) 45 °C/W
θJC T Package, Junction to Case 2
θJA S Package, Junction to Ambient (9) 50
ON /OFF CONTROL Test Circuit Figure 21 and Figure 22
VIH ON /OFF Pin VOUT = 0V 1.4 2.2/2.4 V(Min)
Logic Input Level
VIL VOUT = Nominal Output Voltage 1.2 1.0/0.8 V(Max)
IIH ON /OFF Pin Input ON /OFF Pin = 5V (OFF) 12 μA
Current 30 μA(Max)
IIL ON /OFF Pin = 0V (ON) 0 μA
10 μA(Max)
(1) All limits specified at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits
are 100% production tested. All limits at temperature extremes are specified via correlation using standard Statistical Quality Control
(SQC) methods.
(2) 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%.
(3) Output pin sourcing current. No diode, inductor or capacitor connected to output.
(4) Feedback pin removed from output and connected to 0V.
(5) 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.
(6) VIN = 40V (60V for high voltage version).
(7) Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with ½ inch leads in a
socket, or on a PC board with minimum copper area.
(8) Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with ¼ inch leads
soldered to a PC board containing approximately 4 square inches of copper area surrounding the leads.
(9) If the DDPAK/TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally
connected to the package. Using 0.5 square inches of copper area, θJA is 50°C/W, with 1 square inch of copper area, θJA is 37°C/W,
and with 1.6 or more square inches of copper area, θJA is 32°C/W.
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TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 21 and Figure 22)
Normalized Output Voltage Line Regulation
Figure 2. Figure 3.
Dropout Voltage Current Limit
Figure 4. Figure 5.
Standby
Quiescent Current Quiescent Current
Figure 6. Figure 7.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
(Circuit of Figure 21 and Figure 22)Switch Saturation
Oscillator Frequency Voltage
Figure 8. Figure 9.
Efficiency Minimum Operating Voltage
Figure 10. Figure 11.
Quiescent Current Feedback Voltage
vs Duty Cycle vs Duty Cycle
Figure 12. Figure 13.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
(Circuit of Figure 21 and Figure 22)Quiescent Current
Minimum Operating Voltage vs Duty Cycle
Figure 14. Figure 15.
Feedback Voltage
vs Duty Cycle Feedback Pin Current
Figure 16. Figure 17.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
(Circuit of Figure 21 and Figure 22)
Maximum Power Dissipation
(DDPAK/TO-263) Switching Waveforms
VOUT = 15V
If the DDPAK/TO-263 package is used, the thermal resistance can be A: Output Pin Voltage, 50V/div
reduced by increasing the PC board copper area thermally connected B: Output Pin Current, 2A/div
to the package. Using 0.5 square inches of copper area, θJA is C: Inductor Current, 2A/div
50°C/W, with 1 square inch of copper area, θJA is 37°C/W, and with D: Output Ripple Voltage, 50 mV/div,
1.6 or more square inches of copper area, θJA is 32°C/W. AC-Coupled
Horizontal Time Base: 5 μs/div
Figure 18. Figure 19.
Load Transient Response
Figure 20.
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TEST CIRCUIT AND LAYOUT GUIDELINES
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.
CIN — 100 μF, 75V, Aluminum Electrolytic
COUT — 1000 μF, 25V, Aluminum Electrolytic
D1— Schottky, MBR360
L1— 100 μH, Pulse Eng. PE-92108
R1— 2k, 0.1%
R2— 6.12k, 0.1%
Figure 21. Fixed Output Voltage Versions
where
VREF = 1.23V, R1 between 1k and 5k
Figure 22. Adjustable Output Voltage Version
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LM2576 Series Buck Regulator Design Procedure
PROCEDURE (Fixed Output Voltage Versions) EXAMPLE (Fixed Output Voltage Versions)
Given: Given:
VOUT = Regulated Output Voltage VOUT = 5V
(3.3V, 5V, 12V, or 15V) VIN(Max) = 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 Figure 23,A. Use the selection guide shown in Figure 24.
Figure 24,Figure 25, or Figure 26. (Output voltages of 3.3V, 5V, 12V B. From the selection guide, the inductance area intersected by the
or 15V respectively). For other output voltages, see the design 15V line and 3A line is L100.
procedure for the adjustable version. C. Inductor value required is 100 μH. From the table in Figure 23.
B. From the inductor value selection guide, identify the inductance Choose AIE 415-0930, Pulse Engineering PE92108, or Renco
region intersected by VIN(Max) and ILOAD(Max), and note the RL2444.
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 23. 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 INDUCTOR SELECTION.
2. Output Capacitor Selection (COUT) 2. Output Capacitor Selection (COUT)
A. The value of the output capacitor together with the inductor A. COUT = 680 μF to 2000 μF standard aluminum electrolytic.
defines the dominate pole-pair of the switching regulator loop. For B.Capacitor voltage rating = 20V.
stable operation and an acceptable output ripple voltage,
(approximately 1% of the output voltage) a value between 100 μF
and 470 μF is recommended.
B. The capacitor's voltage rating should be at least 1.5 times greater
than the output voltage. For a 5V regulator, a rating of at least 8V is
appropriate, and a 10V or 15V rating is recommended.
Higher voltage electrolytic capacitors generally have lower ESR
numbers, and for this reason it may be necessary to select a
capacitor rated for a higher voltage than would normally be needed.
3. Catch Diode Selection (D1) 3. Catch Diode Selection (D1)
A.The catch-diode current rating must be at least 1.2 times greater A.For this example, a 3A current rating is adequate.
than the maximum load current. Also, if the power supply design B. Use a 20V 1N5823 or SR302 Schottky diode, or any of the
must withstand a continuous output short, the diode should have a suggested fast-recovery diodes shown in Table 1.
current rating equal to the maximum current limit of the LM2576. The
most stressful condition for this diode is an overload or shorted
output condition.
B. The reverse voltage rating of the diode should be at least 1.25
times the maximum input voltage.
4. Input Capacitor (CIN) 4. Input Capacitor (CIN)
An aluminum or tantalum electrolytic bypass capacitor located close A 100 μF, 25V aluminum electrolytic capacitor located near the input
to the regulator is needed for stable operation. and ground pins provides sufficient bypassing.
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INDUCTOR VALUE SELECTION GUIDES
(For Continuous Mode Operation)
Figure 23. LM2576(HV)-3.3 Figure 24. LM2576(HV)-5.0
Figure 25. LM2576(HV)-12 Figure 26. LM2576(HV)-15
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(For Continuous Mode Operation)
Figure 27. LM2576(HV)-ADJ
PROCEDURE (Adjustable Output Voltage Versions) EXAMPLE (Adjustable Output Voltage Versions)
Given: Given:
VOUT = Regulated Output Voltage VOUT = 10V
VIN(Max) = Maximum Input Voltage VIN(Max) = 25V
ILOAD(Max) = Maximum Load Current ILOAD(Max) = 3A
F = Switching Frequency (Fixed at 52 kHz) F = 52 kHz
1. Programming Output Voltage (Selecting R1 and R2, as shown 1. Programming Output Voltage(Selecting R1 and R2)
in Figure 21 and Figure 22)
Use the following formula to select the appropriate resistor values.
R1can be between 1k and 5k. (For best temperature coefficient and R2= 1k (8.13 −1) = 7.13k, closest 1% value is 7.15k
stability with time, use 1% metal film resistors)
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(For Continuous Mode Operation)
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, E • T (V • μs), A. Calculate 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 C. ILOAD(Max) = 3A
the E • T number on the vertical axis of the Inductor Value D. Inductance Region = H150
Selection Guide shown in Figure 27.E. Inductor Value = 150 μHChoose from AIEpart #415-0936Pulse
C. On the horizontal axis, select the maximum load current. Engineering part #PE-531115, or Renco part #RL2445.
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 Table 2. 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 INDUCTOR SELECTION.
3. Output Capacitor Selection (COUT) 3. Output Capacitor Selection (COUT)
A. 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 the following However, for acceptable output ripple voltage select
requirement: 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 select a capacitor rate for a higher voltage than would
normally 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 A. For this example, a 3.3A current rating is adequate.
than the maximum load current. Also, if the power supply design B. Use a 30V 31DQ03 Schottky diode, or any of the suggested fast-
must withstand a continuous output short, the diode should have a recovery diodes in Table 1.
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 1.
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 located close A 100 μF aluminum electrolytic capacitor located near the input and
to the regulator is needed for stable operation. ground pins provides sufficient bypassing.
To further simplify the buck regulator design procedure, TI 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 (3½″) diskette for IBM compatible computers from a TI office in your area.
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