Page 1
LM2574/LM2574HV
SIMPLE SWITCHER
™
0.5A Step-Down Voltage Regulator
LM2574/LM2574HV SIMPLE SWITCHER 0.5A Step-Down Voltage Regulator
June 1999
General Description
The LM2574 series of regulators are monolithic integrated
circuits that provide all the active functions for a step-down
(buck) switching regulator, capable of driving a 0.5A load
with excellent line and load regulation. These devices are
available in fixed output voltages of 3.3V, 5V, 12V, 15V, and
an adjustable output version.
Requiring aminimumnumber of external components, these
regulators are simple to use and include internal frequency
compensation and a fixed-frequency oscillator.
The LM2574 series offers a high-efficiency replacement for
popular three-terminal linear regulators. Because of its high
efficiency, the copper traces on the printed circuit board are
normally the only heat sinking needed.
A standard series of inductors optimized for use with the
LM2574 are available from several different manufacturers.
This feature greatly simplifies the design of switch-mode
power supplies.
Other features include a guaranteed
put voltage within specified input voltages and output load
conditions, and
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.
±
10%on the oscillator frequency. External
±
4%tolerance on out-
Features
n 3.3V, 5V, 12V, 15V, and adjustable output versions
n Adjustable version output voltage range, 1.23V to 37V
n Guaranteed 0.5A output current
n Wide input voltage range, 40V, up to 60V for HV version
n Requires only 4 external components
n 52 kHz fixed frequency internal oscillator
n TTL shutdown capability, low power standby mode
n High efficiency
n Uses readily available standard inductors
n Thermal shutdown and current limit protection
Applications
n Simple high-efficiency step-down (buck) regulator
n Efficient pre-regulator for linear regulators
n On-card switching regulators
n Positive to negative converter (Buck-Boost)
Typical Application (Fixed Output Voltage Versions)
(57V for HV version)
conditions
±
4%max over line and load
Note: Pin numbers are for 8-pin DIP package.
Patent Pending
SIMPLE SWITCHER
© 1999 National Semiconductor Corporation DS011394 www.national.com
™
is a trademark of National Semiconductor Corporation
DS011394-1
Page 2
Connection Diagrams
8-Lead DIP
* No internal connection, but should be soldered to PC board for best heat
transfer.
DS011394-2
Top View
Order Number LM2574-3.3HVN, LM2574HVN-5.0,
LM2574HVN-12, LM2574HVN-15, LM2574HVN-ADJ,
LM2574N-3.3, LM2574N-5.0, LM2574N-12,
LM2574N-15 or LM2574N-ADJ
See NS Package Number N08A
14-Lead Wide
Surface Mount (WM)
DS011394-3
Top View
Order Number LM2574HVM-3.3, LM2574HVM-5.0,
LM2574HVM-12, LM2574HVM-15, LM2574HVM-ADJ,
LM2574M-3.3 LM2574M-5.0, LM2574M-12,
LM2574M-15 or LM2574M-ADJ
See NS Package Number M14B
www.national.com 2
Page 3
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Maximum Supply Voltage
LM2574 45V
LM2574HV 63V
ON /OFF Pin Input Voltage
Output Voltage to Ground
(Steady State) −1V
Minimum ESD Rating
−0.3V ≤ V ≤ +V
Lead Temperature
(Soldering, 10 seconds) 260˚C
Maximum Junction Temperature 150˚C
Power Dissipation Internally Limited
Operating Ratings
Temperature Range
IN
LM2574/LM2574HV −40˚C ≤ T
Supply Voltage
LM2574 40V
LM2574HV 60V
≤ +125˚C
J
(C=100 pF, R=1.5 kΩ)2kV
Storage Temperature Range −65˚C to +150˚C
LM2574-3.3, LM2574HV-3.3
Electrical Characteristics
12V, I
12V, I
=
25˚C, and those with boldface type apply over full Operating Tempera-
J
LM2574HV-3.3
Typ Limit
(Note 2)
Figure 2
=
100 mA 3.3 V
LOAD
3.234 V(Min)
3.366 V(Max)
≤ 0.5A 3.3 V
LOAD
3.432/3.465 V(Max)
≤ 0.5A 3.3
LOAD
3.450/3.482 V(Max)
=
0.5A 72
LOAD
(Limits)
%
Specifications with standard type face are for T
ture Range.
Symbol Parameter Conditions LM2574-3.3 Units
SYSTEM PARAMETERS (Note 3) Test Circuit
V
OUT
V
OUT
Output Voltage V
Output Voltage 4.75V ≤ VIN≤ 40V, 0.1A ≤ I
=
IN
LM2574 3.168/3.135 V(Min)
V
OUT
Output Voltage 4.75V ≤ VIN≤ 60V, 0.1A ≤ I
LM2574HV 3.168/3.135 V(Min)
η Efficiency V
=
IN
LM2574-5.0, LM2574HV-5.0
Electrical Characteristics
12V, I
12V, I
=
25˚C, and those with boldface type apply over full Operating Tempera-
J
LM2574HV-5.0
Typ Limit
(Note 2)
Figure 2
=
100 mA 5 V
LOAD
4.900 V(Min)
5.100 V(Max)
≤ 0.5A 5 V
LOAD
5.200/5.250 V(Max)
≤ 0.5A 5
LOAD
5.225/5.275 V(Max)
=
0.5A 77
LOAD
(Limits)
%
www.national.com3
Specifications with standard type face are for T
ture Range.
Symbol Parameter Conditions LM2574-5.0 Units
SYSTEM PARAMETERS (Note 3) Test Circuit
V
OUT
V
OUT
Output Voltage V
Output Voltage 7V ≤ VIN≤ 40V, 0.1A ≤ I
=
IN
LM2574 4.800/4.750 V(Min)
V
OUT
Output Voltage 7V ≤ VIN≤ 60V, 0.1A ≤ I
LM2574HV 4.800/4.750 V(Min)
η Efficiency V
=
IN
Page 4
LM2574-12, LM2574HV-12
Electrical Characteristics
25V, I
15V, I
=
25˚C, and those with boldface type apply over full Operating Tempera-
J
LM2574HV-12
Typ Limit
(Note 2)
Figure 2
=
100 mA 12 V
LOAD
11.76 V(Min)
12.24 V(Max)
≤ 0.5A 12 V
LOAD
12.48/12.60 V(Max)
≤ 0.5A 12
LOAD
12.54/12.66 V(Max)
=
0.5A 88
LOAD
(Limits)
%
Specifications with standard type face are for T
ture Range.
Symbol Parameter Conditions LM2574-12 Units
SYSTEM PARAMETERS (Note 3) Test Circuit
V
OUT
V
OUT
Output Voltage V
Output Voltage 15V ≤ VIN≤ 40V, 0.1A ≤ I
=
IN
LM2574 11.52/11.40 V(Min)
V
OUT
Output Voltage 15V ≤ VIN≤ 60V, 0.1A ≤ I
LM2574HV 11.52/11.40 V(Min)
η Efficiency V
=
IN
LM2574-15, LM2574HV-15
Electrical Characteristics
30V, I
18V, I
=
25˚C, and those with boldface type apply over full Operating Tempera-
J
LM2574HV-15
Typ Limit
(Note 2)
Figure 2
=
100 mA 15 V
LOAD
14.70 V(Min)
15.30 V(Max)
≤ 0.5A 15 V
LOAD
15.60/15.75 V(Max)
≤ 0.5A 15
LOAD
15.68/15.83 V(Max)
=
0.5A 88
LOAD
(Limits)
%
Specifications with standard type face are for T
ture Range.
Symbol Parameter Conditions LM2574-15 Units
SYSTEM PARAMETERS (Note 3) Test Circuit
V
OUT
V
OUT
Output Voltage V
Output Voltage 18V ≤ VIN≤ 40V, 0.1A ≤ I
=
IN
LM2574 14.40/14.25 V(Min)
V
OUT
Output Voltage 18V ≤ VIN≤ 60V, 0.1A ≤ I
LM2574HV 14.40/14.25 V(Min)
η Efficiency V
=
IN
LM2574-ADJ, LM2574HV-ADJ
Electrical Characteristics
Specifications with standard type face are for T
ture Range. Unless otherwise specified, V
Symbol Parameter Conditions LM2574-ADJ Units
SYSTEM PARAMETERS (Note 3) Test Circuit
V
FB
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Feedback Voltage V
=
IN
IN
12V, I
=
25˚C, and those with boldface type apply over full Operating Tempera-
J
=
12V, I
LOAD
=
100 mA.
LM2574HV-ADJ
Typ Limit
(Note 2)
Figure 2
=
100 mA 1.230 V
LOAD
1.217 V(Min)
1.243 V(Max)
(Limits)
Page 5
LM2574-ADJ, LM2574HV-ADJ
Electrical Characteristics
Specifications with standard type face are for T
ture Range. Unless otherwise specified, V
Symbol Parameter Conditions LM2574-ADJ Units
SYSTEM PARAMETERS (Note 3) Test Circuit
V
FB
V
FB
η Efficiency V
Feedback Voltage 7V ≤ VIN≤ 40V, 0.1A ≤ I
LM2574 V
Feedback Voltage 7V ≤ VIN≤ 60V, 0.1A ≤ I
LM2574HV V
(Continued)
=
25˚C, and those with boldface type apply over full Operating Tempera-
J
=
12V, I
IN
LOAD
=
Figure 2
Programmed for 5V. Circuit of
OUT
Programmed for 5V. Circuit of
OUT
=
12V, V
IN
OUT
LOAD
LOAD
=
5V, I
LOAD
100 mA.
LM2574HV-ADJ
Typ Limit
(Note 2)
≤ 0.5A 1.230 V
Figure 2
1.193/1.180 V(Min)
1.267/1.280 V(Max)
≤ 0.5A 1.230
Figure 2
1.193/1.180 V(Min)
1.273/1.286 V(Max)
=
0.5A 77
(Limits)
%
All Output Voltage Versions
Electrical Characteristics
Specifications with standard type face are for T
ture Range. Unless otherwise specified, V
=
and V
30V for the 15V version. I
IN
LOAD
Symbol Parameter Conditions LM2574-XX Units
DEVICE PARAMETERS
I
b
f
O
V
SAT
Feedback Bias
Current
Oscillator Frequency (see Note 10) 52 kHz
Saturation Voltage I
DC Max Duty Cycle
Adjustable Version Only, V
OUT
(Note 5) 98
(ON)
I
CL
I
L
Current Limit Peak Current, (Notes 4, 10) 1.0 A
Output Leakage (Notes 6, 7) Output=0V 2 mA(Max)
Current Output=−1V 7.5 mA
I
Q
I
STBY
Quiescent Current (Note 6) 5 mA
Standby Quiescent ON /OFF Pin=5V (OFF) 50 µA
Current 200 µA(Max)
θ
JA
θ
JA
θ
JA
θ
JA
Thermal Resistance N Package, Junction to Ambient (Note 8) 92
N Package, Junction to Ambient (Note 9) 72 ˚C/W
M Package, Junction to Ambient (Note 8) 102
M Package, Junction to Ambient (Note 9) 78
=
25˚C, and those with boldface type apply over full Operating Tempera-
J
=
12V for the 3.3V, 5V, and Adjustable version, V
IN
=
100 mA.
=
25V for the 12V version,
IN
LM2574HV-XX
Typ Limit
(Note 2)
=
5V 50 100/500 nA
OUT
47/42 kHz(Min)
58/63 kHz(Max)
=
0.5A (Note 4) 0.9 V
1.2/1.4 V(max)
93
0.7/0.65 A(Min)
1.6/1.8 A(Max)
Output=−1V 30 mA(Max)
10 mA(Max)
(Limits)
%
%
(Min)
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Page 6
All Output Voltage Versions
Electrical Characteristics
Specifications with standard type face are for T
ture Range. Unless otherwise specified, V
=
and V
Symbol Parameter Conditions LM2574-XX Units
ON /OFF CONTROL Test Circuit
V
IH
V
IL
I
H
I
IL
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: All limits guaranteed at room temperature (Standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%produc-
tion tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate
Average Outgoing Quality Level.
Note 3: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM2574
is used as shown in the
Note 4: Output pin sourcing current. No diode, inductor or capacitor connected to output pin.
Note 5: Feedback pin removed from output and connected to 0V.
Note 6: Feedback pin removed from output and connected to +12V for the Adjustable, 3.3V, and 5V versions, and +25V for the 12V and 15V versions, to force the
output transistor OFF.
Note 7: V
Note 8: Junction to ambient thermal resistance with approximately 1 square inch of printed circuit board copper surrounding the leads. Additional copper area will
lower thermal resistance further. See application hints in this data sheet and the thermal model in Switchers Made Simple software.
Note 9: Junction to ambient thermal resistance with approximately 4 square inches of 1 oz. (0.0014 in. thick) printed circuit board copper surrounding the leads. Ad-
ditional copper area will lower thermal resistance further. (See Note 8.)
Note 10: The oscillator frequency reduces to approximately 18 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%.
30V for the 15V version. I
IN
Figure 2
ON /OFF Pin Logic V
Input Level V
ON /OFF Pin Input ON /OFF Pin=5V (OFF) 12 µA
Current 30 µA(Max)
Figure 2
test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.
=
40V (60V for high voltage version).
IN
(Continued)
=
25˚C, and those with boldface type apply over full Operating Tempera-
J
LOAD
=
12V for the 3.3V, 5V, and Adjustable version, V
IN
=
100 mA.
=
25V for the 12V version,
IN
LM2574HV-XX
(Limits)
Typ Limit
(Note 2)
=
0V 1.4 2.2/2.4 V(Min)
OUT
=
Nominal Output Voltage 1.2 1.0/0.8 V(Max)
OUT
ON /OFF Pin=0V (ON) 0µA
10 µA(Max)
Typical Performance Characteristics (Circuit of
Normalized Output Voltage
DS011394-27
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Line Regulation
Figure 2
DS011394-28
)
Dropout Voltage
DS011394-29
Page 7
Typical Performance Characteristics (Circuit of
Figure 2
) (Continued)
Current Limit
Oscillator Frequency
Minimum Operating Voltage
DS011394-30
DS011394-33
Supply Current
Switch Saturation
Voltage
Supply Current
vs Duty Cycle
Standby
Quiescent Current
DS011394-31
DS011394-32
Efficiency
DS011394-35
DS011394-34
Feedback Voltage
vs Duty Cycle
DS011394-36
DS011394-37
DS011394-38
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Page 8
Typical Performance Characteristics (Circuit of
Figure 2
) (Continued)
Feedback
Pin Current
DS011394-39
Continuous Mode Switching Waveforms
=
V
5V, 500 mA Load Current, L=330 µH
OUT
Notes:
A: Output Pin Voltage, 10V/div
B: Inductor Current, 0.2 A/div
C: Output Ripple Voltage, 20 mV/div,
AC-Coupled
Horizontal Time Base: 5 µs/div
DS011394-6
Junction to Ambient
Thermal Resistance
DS011394-40
Discontinuous Mode Switching Waveforms
=
V
5V, 100 mA Load Current, L=100 µH
OUT
Notes:
A: Output Pin Voltage, 10V/div
B: Inductor Current, 0.2 A/div
C: Output Ripple Voltage, 20 mV/div,
AC-Coupled
Horizontal Time Base: 5 µs/div
DS011394-7
500 mA Load Transient Response for Continuous
Mode Operation. L=330 µH, C
Notes:
A: Output Voltage, 50 mV/div.
AC Coupled
B: 100 mA to 500 mA Load Pulse
Horizontal Time Base: 200 µs/div
OUT
=
300 µF
DS011394-8
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250 mA Load Transient Response for Discontinuous
Mode Operation. L=68 µH, C
Notes:
A: Output Voltage, 50 mV/div.
AC Coupled
B: 50 mA to 250 mA Load Pulse
Horizontal Time Base: 200 µs/div
OUT
=
470 µF
DS011394-9
Page 9
Block Diagram
R1=1k
3.3V, R2=1.7k
5V, R2=3.1k
12V, R2=8.84k
15V, R2=11.3k
For Adj. Version
R1=Open, R2=0Ω
Note: Pin numbers are for the 8-pin DIP package.
DS011394-10
FIGURE 1.
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Page 10
Test Circuit and Layout Guidelines
Fixed Output Voltage Versions
CIN— 22 µF, 75V
Aluminum Electrolytic
— 220 µF, 25V
C
OUT
Aluminum Electrolytic
D1 — Schottky, 11DQ06
L1 — 330 µH, 52627
(for 5V in, 3.3V out, use
100 µH, RL-1284-100)
R1 — 2k, 0.1
R2 — 6.12k, 0.1
%
%
Adjustable Output Voltage Version
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 pos-
sible. 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.
DS011394-11
DS011394-12
FIGURE 2.
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Page 11
Test Circuit and Layout Guidelines
(Continued)
Inductor Pulse Eng. Renco NPI
Value (Note 1) (Note 2) (Note 3)
68 µH
100 µH
150 µH 52625 RL-1284-150-43 NP5917
220 µH 52626 RL-1284-220-43 NP5918/5919
330 µH 52627 RL-1284-330-43 NP5920/5921
470 µH 52628 RL-1284-470-43 NP5922
680 µH 52629 RL-1283-680-43 NP5923
1000 µH 52631 RL-1283-1000-43
1500 µH
2200 µH
*
RL-1284-68-43 NP5915
*
RL-1284-100-43 NP5916
*
RL-1283-1500-43
*
RL-1283-2200-43
FIGURE 3. Inductor Selection by
Manufacturer’s Part Number
*
*
*
U.S. Source
Note 1: Pulse Engineering, (619) 674-8100
P.O. Box 12236, San Diego, CA 92112
Note 2: Renco Electronics Inc., (516) 586-5566
60 Jeffryn Blvd. East, Deer Park, NY 11729
*
Contact Manufacturer
European Source
Note 3: NPI/APC +44 (0) 634 290588
47 Riverside, Medway City Estate
Strood, Rochester, Kent ME2 4DP. UK
*
Contact Manufacturer
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Page 12
LM2574 Series Buck Regulator Design Procedure
PROCEDURE (Fixed Output Voltage Versions) EXAMPLE (Fixed Output Voltage Versions)
Given:
=
V
Regulated Output Voltage (3.3V, 5V, 12V, or 15V)
OUT
(Max)=Maximum Input Voltage
V
IN
(Max)=Maximum Load Current
I
LOAD
1. Inductor Selection (L1)
A. Select the correct Inductor value selection guide from
ures 4, 5, 6
,or
Figure 7
. (Output voltages of 3.3V, 5V, 12V or
Fig-
15V respectively). For other output voltages, see the design
procedure for the adjustable version.
B. From the inductor value selection guide, identify the inductance region intersected by V
C. Select an appropriate inductor from the table shown in
ure 3
. Part numbers are listed for three inductor manufactur-
(Max) and I
IN
LOAD
(Max).
Fig-
ers. The inductor chosen must be rated for operation at the
LM2574 switching frequency (52 kHz) and for a current rating
of 1.5 x I
ductor section in the Application Hints section of this data
. For additional inductor information, see the in-
LOAD
sheet.
2. Output Capacitor Selection (C
OUT
)
A. The value of the output capacitor together with the inductor
defines the dominate pole-pair of the switching regulator loop.
For stable operation and an acceptable output ripple voltage,
(approximately 1%of the output voltage) a value between
100 µF and 470 µF is recommended.
B. The capacitor’s voltage rating should be at least 1.5 times
greater than the output voltage. For a 5V regulator, a rating of
at least 8V is appropriate, and a 10V or 15V rating is recommended.
Higher voltage electrolytic capacitors generally have lower
ESR numbers, and for this reason it may be necessary to select a capacitor rated for a higher voltage than would normally
be needed.
3. Catch Diode Selection (D1)
A. The catch-diode current rating must be at least 1.5 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 LM2574. 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 (C
)
IN
An aluminum or tantalum electrolytic bypass capacitor located
close to the regulator is needed for stable operation.
Given:
=
V
5V
OUT
(Max)=15V
V
IN
(Max)=0.4A
I
LOAD
1. Inductor Selection (L1)
A. Use the selection guide shown in
Figure 5
B. From the selection guide, the inductance area intersected
by the 15V line and 0.4A line is 330.
C. Inductor value required is 330 µH. From the table in
3
, choose Pulse Engineering PE-52627, Renco RL-1284-330,
or NPI NP5920/5921.
2. Output Capacitor Selection (C
=
A. C
100 µF to 470 µF standard aluminum electrolytic.
OUT
OUT
)
B. Capacitor voltage rating=20V.
3. Catch Diode Selection (D1)
A. For this example, a 1A current rating is adequate.
B. Use a 20V 1N5817 or SR102 Schottky diode, or any of the
suggested fast-recovery diodes shown in
4. Input Capacitor (CIN)
A22 µF aluminum electrolytic capacitor located near the input
and ground pins provides sufficient bypassing.
.
Figure 9
Figure
.
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Page 13
LM2574 Series Buck Regulator Design Procedure (Continued)
INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation)
DS011394-26
FIGURE 4. LM2574HV-3.3 Inductor Selection Guide
FIGURE 6. LM2574HV-12 Inductor Selection Guide
DS011394-14
DS011394-13
FIGURE 5. LM2574HV-5.0 Inductor Selection Guide
DS011394-15
FIGURE 7. LM2574HV-15 Inductor Selection Guide
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Page 14
LM2574 Series Buck Regulator Design Procedure (Continued)
DS011394-16
FIGURE 8. LM2574HV-ADJ Inductor Selection Guide
PROCEDURE (Adjustable Output Voltage Versions) EXAMPLE (Adjustable Output Voltage Versions)
Given:
=
Regulated Output Voltage
V
OUT
(Max)=Maximum Input Voltage
V
IN
(Max)=Maximum Load Current
I
LOAD
F=Switching Frequency
1. Programming Output Voltage
shown in Figure 2
(Fixed at 52 kHz)
(Selecting R1 and R2, as
)
Use the following formula to select the appropriate resistor
values.
Given:
=
V
24V
OUT
(Max)=40V
V
IN
(Max)=0.4A
I
LOAD
F=52 kHz
1. Programming Output Voltage
(Selecting R1 and R2)
R1can be between 1k and 5k.
(For best temperature coeffi-
cient and stability with time, use 1%metal film resistors)
2. Inductor Selection (L1)
A. Calculate the inductor Volt
T(V•µs), from the following formula:
E
•
microsecond constant,
•
B. Use the E•T value from the previous formula and match
it with the E
Value Selection Guide shown in
T number on the vertical axis of the Inductor
•
Figure 8
.
C. On the horizontal axis, select the maximum load current.
D. Identify the inductance region intersected by the E
T
•
value and the maximum load current value, and note the inductor value for that region.
E. Select an appropriate inductor from the table shown in
ure 3
. Part numbers are listed for three inductor manufactur-
Fig-
ers. The inductor chosen must be rated for operation at the
LM2574 switching frequency (52 kHz) and for a current rating
of 1.5 x I
ductor section in the application hints section of this data
. For additional inductor information, see the in-
LOAD
sheet.
www.national.com 14
=
R
1k (19.51−1)=18.51k, closest 1%value is 18.7k
2
2. Inductor Selection (L1)
A. Calculate E
T(V•µs)
•
B. E•T=185 V•µs
(Max)=0.4A
C. I
LOAD
D. Inductance Region=1000
E. Inductor Value=1000 µH
#
ing Part
PE-52631, or
Choose from Pulse Engineer-
Renco
Part#RL-1283-1000.
Page 15
LM2574 Series Buck Regulator Design Procedure (Continued)
PROCEDURE (Adjustable Output Voltage Versions) EXAMPLE (Adjustable Output Voltage Versions)
3. Output Capacitor Selection (C
OUT
)
A. The value of the output capacitor together with the inductor
defines the dominate pole-pair of the switching regulator loop.
For stable operation, the capacitor must satisfy the following
requirement:
The above formula yields capacitor values between 5 µF and
1000 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 24V regulator, a rating
of at least 35V is recommended.
Higher voltage electrolytic capacitors generally have lower
ESR numbers, and for this reasion it may be necessary to select a capacitor rate for a higher voltage than would normally
be needed.
4. Catch Diode Selection (D1)
A. The catch-diode current rating must be at least 1.5 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 LM2574. The most stressful condition for this
diode is an overload or shorted output condition. Suitable di-
Figure 9
odes are shown in the selection guide of
.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
5. Input Capacitor (C
)
IN
An aluminum or tantalum electrolytic bypass capacitor located
close to the regulator is needed for stable operation.
3. Output Capacitor Selection (C
OUT
)
However, for acceptable output ripple voltage select
≥ 100 µF
C
OUT
=
C
100 µF electrolytic capacitor
OUT
4. Catch Diode Selection (D1)
A. For this example, a 1A current rating is adequate.
B. Use a 50V MBR150 or 11DQ05 Schottky diode, or any of
the suggested fast-recovery diodes in
Figure 9
.
5. Input Capacitor (CIN)
A22 µF aluminum electrolytic capacitor located near the input
and ground pins provides sufficient bypassing. See (
To further simplify the buck regulator design procedure, National Semiconductor is making available computer design
software to be used with the Simple Switcher line of switching
regulators. Switchers Made Simple (version 3.3) is available
1
ona(3
⁄2") diskette for IBM compatible computers from a Na-
tional Semiconductor sales office in your area.
Figure 9
).
www.national.com15
Page 16
LM2574 Series Buck Regulator Design Procedure (Continued)
V
R
Schottky Fast Recovery
20V 1N5817
SR102
MBR120P
30V 1N5818
SR103
11DQ03 The
MBR130P following
10JQ030 diodes
40V 1N5819 are all
SR104 rated to
11DQ04 100V
11JQ04
MBR140P
50V MBR150 11DF1
SR105 10JF1
11DQ05 MUR110
11JQ05 HER102
60V MBR160
SR106
11DQ06
11JQ06
90V 11DQ09
FIGURE 9. Diode Selection Guide
Application Hints
INPUT CAPACITOR (CIN)
To maintain stability, the regulator input pin must be bypassed with at least a 22 µF electrolytic capacitor. The capacitor’s leads must be kept short, and located 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 will increase the regulator stability at cold temperatures. For maximum capacitor operating lifetime, the
capacitor’s RMS ripple current rating should be greater than
1 Amp Diodes
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 LM2574 (or any of the Simple Switcher family) can be
used for both continuous and discontinuous modes of operation.
In many cases the preferred mode of operation is in the continuous mode. It offers better load regulation, lower peak
switch, inductor and diode currents, and can have lower output ripple voltage. But it does require relatively large inductor
values to keep the inductor current flowing continuously, especially at low output load currents.
To simplify the inductor selection process, an inductor selection guide (nomograph) was designed (see
Figure 8
). This guide assumes continuous mode operation,
and selects an inductor that will allow a peak-to-peak inductor ripple current (∆I
maximum design load current. In the LM2574 SIMPLE
SWITCHER, the peak-to-peak inductor ripple current percentage (of load current) is allowed to change as different
design load currents are selected. By allowing the percentage of inductor ripple current to increase for lower current
applications, the inductor size and value can be kept relatively low.
) to be a certain percentage of the
IND
Figure 4
through
www.national.com 16
Page 17
Application Hints (Continued)
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 will reach zero, and the
switcher will change to a discontinuous mode of operation.
This is a perfectly acceptable mode of operation. Any buck
switching regulator (no matter how large the inductor value
is) will be forced to run discontinuous if the load current is
light enough.
The curve shown in
peak inductor ripple current (∆I
different maximum load currents are selected, and also how
it changes as the operating point varies from the upper border to the lower border within an inductance region (see Inductor Selection guides).
FIGURE 10. Inductor Ripple Current (∆I
Based on Selection Guides from
Consider the following example:
=
5V
V
OUT
=
V
10V minimum up to 20V maximum
IN
The selection guide in
current, and an input voltage range between 10V and 20V,
the inductance region selected by the guide is 330 µH. This
value of inductance will allow a peak-to-peak inductor ripple
current (∆I
mum load current. For this inductor value, the ∆I
IND
vary depending on the input voltage. As the input voltage increases to 20V, it approaches the upper border of the inductance region, and the inductor ripple current increases. Referring to the curve in
0.4A load current level, and operating near the upper border
of the 330 µH inductance region, the ∆I
0.4A, or 212 mA p-p.
This ∆I
inductor current rating can be determined, the minimum load
is important because from this number the peak
IND
current required before the circuit goes to discontinuous operation, and also, knowing the ESR of the output capacitor,
@
Figure 10
0.4A
illustrates how the peak-to-
) is allowed to change as
IND
Figure 4
Figure 8
.
Figure 5
shows that for a 0.4A load
DS011394-18
) Range
IND
through
) to flow that will be a percentage of the maxi-
will also
IND
Figure 10
, it can be seen that at the
will be 53%of
IND
the output ripple voltage can be calculated, or conversely,
measuring the output ripple voltage and knowing the ∆I
the ESR can be calculated.
IND
From the previous example, the Peak-to-peak Inductor
Ripple Current (∆I
known, the following three formulas can be used to calculate
)=212 mA p-p. Once the ∆
IND
IND
value is
additional information about the switching regulator circuit:
1. Peak Inductor or peak switch current
2. Minimum load current before the circuit becomes discontinuous
3. Output Ripple Voltage=(∆I
) x (ESR of C
IND
OUT
)
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.The computer design software
Switchers Made Simple
will provide all component
values for discontinuous (as well as continuous) mode of operation.
Inductors are available in different styles such as pot core,
toroid, E-frame, bobbin core, etc., as well as different core
materials, such as ferrites and powdered iron. The least expensive, the bobbin core type, consists of wire wrapped on a
ferrite rod core. This type of construction makes for an inexpensive inductor, but since the magnetic flux is not completely contained within the core, it generates more electromagnetic interference (EMI). This EMl 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 powdered
iron toroid for Pulse Engineering, and ferrite bobbin core for
Renco.
An inductor should not be operated 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). This can cause the inductor current to rise very
rapidly and will affect the energy storage capabilities of the
inductor and could cause inductor overheating. Different inductor types have different saturation characteristics, and
this should be kept in mind when selecting an inductor. The
inductor manufacturers’ data sheets include current and energy limits to avoid inductor saturation.
OUTPUT CAPACITOR
An output capacitor is required tofilter the output voltage and
is needed for loop stability. The capacitor should be located
near the LM2574 using short pc board traces. Standard aluminum electrolytics are usually adequate, but low ESR types
are recommended for low output ripple voltage and good
stability. The ESR of a capacitor depends on many factors,
some which are: the value, the voltage rating, physical size
and the type of construction. In general, low value or low
voltage (less than 12V) electrolytic capacitors usually have
higher ESR numbers.
The amount of output ripple voltage is primarily a function of
the ESR (Equivalent Series Resistance) of the output ca-
,
www.national.com17
Page 18
Application Hints (Continued)
pacitor and the amplitude of the inductor ripple current
(∆I
). See the section on inductor ripple current in Applica-
IND
tion Hints.
The lower capacitor values (100 µF- 330 µF) will allow typi-
cally 50 mV to 150 mV of output ripple voltage, while largervalue capacitors will reduce the ripple to approximately
20 mV to 50 mV.
Output Ripple Voltage=(∆I
To further reduce the output ripple voltage, several standard
electrolytic capacitors may be paralleled, or a higher-grade
capacitor may be used. Such capacitors are often called
“high-frequency,” “low-inductance,” or “low-ESR.” These will
reduce the output ripple to 10 mV or 20 mV.However, when
operating in the continuous mode, reducing the ESR below
0.03Ω can cause instability in the regulator.
Tantalum capacitors can have a very low ESR, and should
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 capacitor’s ripple current rating at 52 kHz should be at
least 50%higher than the peak-to-peak inductor ripple current.
CATCH DIODE
Buck regulators require a diode to provide a return path for
the inductor current when the switch is off. This diode should
be located close to the LM2574 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
5V). 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 (e.g., 1N4001 or
1N5400, etc.) are also not suitable. See
tky and “soft” fast-recovery diode selection guide.
OUTPUT VOLTAGE RIPPLE AND TRANSIENTS
The output voltage of a switching power supply will contain a
sawtooth ripple voltage at the switcher frequency, typically
about 1%of the output voltage, and may also contain short
voltage spikes at the peaks of the sawtooth waveform.
The output ripple voltage is due mainly to the inductor sawtooth ripple current multiplied by the ESR of the output capacitor. (See the inductor selection in the application hints.)
The voltage spikes are present because of the 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 & 100 µF) can be added
to the output (as shown in
amount of output ripple and transients. A 10 x reduction in
output ripple voltage and transients is possible with this filter.
) (ESR of C
IND
Figure 16
)
OUT
Figure 9
for Schot-
) to further reduce the
FEEDBACK CONNECTION
The LM2574 (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 LM2574
to avoid picking up unwanted noise. Avoid using resistors
greater than 100 kΩ because of the increased chance of
noise pickup.
ON /OFF INPUT
For normal operation, the ON /OFF pin should be grounded
or driven with a low-level TTL voltage (typically below 1.6V).
To put the regulator into standby mode, drive this pin with a
high-level TTL or CMOS signal. The ON /OFF pin can be
safely pulled up to +VINwithout a resistor in series with it.
The ON /OFF pin should not be left open.
GROUNDING
The 8-pin molded DIP and the 14-pin surface mount package have separate power and signal ground pins. Both
ground pins should be soldered directly to wide printed circuit board copper traces to assure low inductance connections and good thermal properties.
THERMAL CONSIDERATIONS
The 8-pin DIP (N) package and the 14-pin Surface Mount
(M) package are molded plastic packages with solid copper
lead frames. The copper lead frame conducts the majority of
the heat from the die, through the leads, to the printed circuit
board copper, which acts as the heat sink. For best thermal
performance, wide copper traces should be used, and all
ground and unused pins should be soldered to generous
amounts of printed circuit board copper, such as a ground
plane. Large areas of copper provide the best transfer of
heat (lower thermal resistance) to the surrounding air, and
even double-sided or multilayer boards provide better heat
paths to the surrounding air. Unless the power levels are
small, using a socket for the 8-pin package is not recommended because of the additional thermal resistance it introduces, and the resultant higher junction temperature.
Because of the 0.5A current rating of the LM2574, the total
package power dissipation for this switcher is quite low,
ranging from approximately 0.1W up to 0.75W under varying
conditions. In a carefully engineered printed circuit board,
both the N and the M package can easily dissipate up to
0.75W, even at ambient temperatures of 60˚C, and still keep
the maximum junction temperature below 125˚C.
A curve displaying thermal resistance vs. pc board area for
the two packages is shown in the Typical Performance Characteristics curves section of this data sheet.
These thermal resistance numbers are approximate, and
there can be many factors that will affect the final thermal resistance. Some of these factors include board size, shape,
thickness, position, location, and board temperature. Other
factors are, the area of printed circuit copper, copper thickness, trace width, multi-layer, single- or double-sided, and
the amount of solder on the board. The effectiveness of the
pc board to dissipate heat also depends on the size, number
and spacing of other components on the board. Furthermore, some of these components, such as the catch diode
and inductor will generate some additional heat. Also, the
thermal resistance decreases as the power level increases
because of the increased air current activity at the higher
power levels, and the lower surface to air resistance coefficient at higher temperatures.
www.national.com 18
Page 19
Application Hints (Continued)
The data sheet thermal resistance curves and the thermal
model in
can estimate the maximum junction temperature based on
operating conditions. ln addition, the junction temperature
can be estimated in actual circuit operation by using the following equation.
T
With the switcher operating under worst case conditions and
all other components on the board in the intended enclosure,
measure the copper temperature (T
be done by temporarily soldering a small thermocouple to
the pc board copper near the IC, or by holding a small thermocouple on the pc board copper using thermal grease for
good thermal conduction.
The thermal resistance (θ
θ
θ
Switchers Made Simple
=
+(θ
T
j
cu
=
42˚C/W for the N-8 package
j-cu
=
52˚C/W for the M-14 package
j-cu
j-cuxPD
)
software (version 3.3)
) near the IC. This can
cu
) for the two packages is:
j-cu
The power dissipation (P
it can be estimated by using the formula:
) for the IC could be measured, or
D
Where ISis obtained from the typical supply current curve
(adjustable version use the supply current vs. duty cycle
curve).
Additional Applications
INVERTING REGULATOR
Figure 11
to generate a negative 12V output from a positive input voltage. This circuit bootstraps the regulator’s ground pin to the
negative output voltage, then by grounding the feedback pin,
the regulator senses the inverted output voltage and regulates it to −12V.
shows a LM2574-12 in a buck-boost configuration
Note: Pin numbers are for the 8-pin DIP package.
FIGURE 11. Inverting Buck-Boost Develops −12V
For an input voltage of 8V or more, the maximum available
output current in this configuration is approximately 100 mA.
At lighter loads, the minimum input voltage required drops to
approximately 4.7V.
The switch currents in this buck-boost configuration are
higher than in the standard buck-mode design, thus lowering
the available output current. Also, the start-up input current
of the buck-boost converter is higher than the standard buckmode regulator, and this may overload an input power
source with a current limit less than 0.6A. Using a delayed
turn-on or an undervoltage lockout circuit (described in the
next section) would allow the input voltage to rise to a high
enough level before the switcher would be allowed to turn
on.
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 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 from the following formula:
DS011394-19
Where f
rent operating conditions, the minimum V
worst case. Select an inductor that is rated for the peak cur-
=
52 kHz. Under normal continuous inductor cur-
osc
represents the
IN
rent anticipated.
Also, the maximum voltage appearing across the regulator is
the absolute sum of the input and output voltage. For a −12V
output, the maximum input voltage for the LM2574 is +28V,
or +48V for the LM2574HV.
The
Switchers Made Simple
version 3.3) design software
can be used to determine the feasibility of regulator designs
using different topologies, different input-output parameters,
different components, etc.
NEGATIVE BOOST REGULATOR
Another variation on the buck-boost topology is the negative
boost configuration. The circuit in
Figure 12
accepts an input
voltage ranging from −5V to −12V and provides a regulated
−12V output. Input voltages greater than −12V will cause the
output to rise above −12V, but will not damage the regulator.
www.national.com19
Page 20
Additional Applications (Continued)
Note: Pin numbers are for 8-pin DIP package.
DS011394-20
FIGURE 12. 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.
UNDERVOLTAGE LOCKOUT
In some applications it is desirable to keep the regulator off
until the input voltage reaches a certain threshold. An undervoltage lockout circuit which accomplishes this task is shown
in
Figure 13
while
Figure 14
shows the same circuit applied
to a buck-boost configuration. These circuits keep the regulator off until the input voltage reaches a predetermined
level.
V
≈ VZ1+2VBE(Q1)
TH
Note: Complete circuit not shown.
Note: Pin numbers are for 8-pin DIP package.
DS011394-21
FIGURE 13. Undervoltage Lockout for Buck Circuit
Note: Complete circuit not shown (see
Note: Pin numbers are for 8-pin DIP package.
Figure 11
DS011394-22
).
FIGURE 14. Undervoltage Lockout
for Buck-Boost Circuit
DELAYED STARTUP
The ON /OFF pin can be used to provide a delayed startup
feature as shown in
Figure 15
. With an input voltage of 20V
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.
ADJUSTABLE OUTPUT, LOW-RIPPLE POWER SUPPLY
A 500 mA power supply that features an adjustable output
voltage is shown in
Figure 16
.An additional L-C filter that reduces the output ripple by a factor of 10 or more is included
in this circuit.
www.national.com 20
Note: Complete circuit not shown.
Note: Pin numbers are for 8-pin DIP package.
FIGURE 15. Delayed Startup
DS011394-23
Page 21
Additional Applications (Continued)
Note: Pin numbers are for 8-pin DIP package.
FIGURE 16. 1.2V to 55V Adjustable 500 mA Power Supply with Low Output Ripple
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.
CATCH DIODE OR CURRENT STEERING DIODE
The diode which provides a return path for the load current
when the LM2574 switch is OFF.
EFFICIENCY (η)
The proportion of input power actually delivered to the load.
CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)
The purely resistive component of a real capacitor’s impedance (see
pacitor 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.
Most standard aluminum electrolytic capacitors in the
100 µF–1000 µF range have 0.5Ω to 0.1Ω ESR. Higher-
Figure 17
). It causes power loss resulting in ca-
DS011394-25
FIGURE 17. Simple Model of a Real Capacitor
DS011394-24
grade capacitors (“low-ESR”, “high-frequency”, or “lowinductance”) in the 100 µF–1000 µF range generally have
ESR of less than 0.15Ω.
EQUIVALENT SERIES INDUCTANCE (ESL)
The pure inductance component of a capacitor (see
17
). The amount of inductance is determined to a large ex-
Figure
tent 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 (∆I
to-peak value of this sawtooth ripple current can be deter-
). The peak-
IND
mined by reading the Inductor Ripple Current section of the
Application hints.
CAPACITOR RIPPLE CURRENT
RMS value of the maximum allowable alternating current at
which a capacitor can be operated continuously at a specified temperature.
STANDBY QUIESCENT CURRENT (I
STBY
)
Supply current required by the LM2574 when in the standby
mode (ON/OFF pin is driven to TTL-high voltage, thus turning the output switch OFF).
INDUCTOR RIPPLE CURRENT (∆I
)
IND
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).
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.
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Page 22
Definition of Terms (Continued)
INDUCTOR SATURATION
The condition which exists when an inductor cannot hold any
more magnetic flux. When an inductor saturates, the inductor appears less inductiveand 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
The product (in VoIt
and the time the voltage is applied. This E
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.
µs) of the voltageapplied to the inductor
•
Topconstant is a
•
Top)
•
www.national.com 22
Page 23
Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LM2574M-3.3, LM2574HVM-3.3, LM2574M-5.0,
LM2574HVM-5.0, LM2574M-12, LM2574HVM-12, LM2574M-15,
14-Lead Wide Surface Mount (WM)
LM2574HVM-15, LM2574M-ADJ or LM2574HVM-ADJ
NS Package Number M14B
www.national.com23
Page 24
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Order Number LM2574M-3.3, LM2574HVM-3.3, LM2574HVN-5.0, LM2574HVN-12,
8-Lead DIP (N)
LM2574HVN-15, LM2574HVN-ADJ, LM2574N-5.0,
LM2574N-12, LM2574N-15 or LM2574N-ADJ
NS Package Number N08A
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
LM2574/LM2574HV SIMPLE SWITCHER 0.5A Step-Down Voltage Regulator
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
labeling, can be reasonably expected to result in a
significant injury to the user.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
www.national.com
National Semiconductor
Europe
Fax: +49 (0) 1 80-530 85 86
Email: europe.support@nsc.com
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English Tel: +49 (0) 1 80-532 78 32
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Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: sea.support@nsc.com
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Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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