LM2575MADJEP [NSC]
IC 3.2 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, PDSO24, SOP-24, Switching Regulator or Controller;型号: | LM2575MADJEP |
厂家: | National Semiconductor |
描述: | IC 3.2 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, PDSO24, SOP-24, Switching Regulator or Controller 开关 光电二极管 |
文件: | 总27页 (文件大小:1099K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
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December 2004
LM2575EP/LM2575HVEP
SIMPLE SWITCHER® 1A Step-Down Voltage Regulator
ENHANCED PLASTIC
General Description
•
Extended Temperature Performance of
−40˚C ≤ TJ ≤ +125˚C
The LM2575EP series of regulators are monolithic inte-
grated circuits that provide all the active functions for a
step-down (buck) switching regulator, capable of driving a
1A load with excellent line and load regulation. These de-
vices are available in fixed output voltages of 3.3V, 5V, 12V,
15V, and an adjustable output version.
•
•
•
•
•
Baseline Control - Single Fab & Assembly Site
Process Change Notification (PCN)
Qualification & Reliability Data
Solder (PbSn) Lead Finish is standard
Requiring a minimum number of external components, these
regulators are simple to use and include internal frequency
compensation and a fixed-frequency oscillator.
Enhanced Diminishing Manufacturing Sources (DMS)
Support
The LM2575EP series offers a high-efficiency replacement
for popular three-terminal linear regulators. It substantially
reduces the size of the heat sink, and in many cases no heat
sink is required.
Features
n 3.3V, 5V, 12V, 15V, and adjustable output versions
n Adjustable version output voltage range,
1.23V to 37V (57V for HV version) 4% max over
line and load conditions
A standard series of inductors optimized for use with the
LM2575EP are available from several different manufactur-
ers. This feature greatly simplifies the design of switch-mode
power supplies.
n Guaranteed 1A output current
n Wide input voltage range, 40V up to 60V for HV version
n Requires only 4 external components
n 52 kHz fixed frequency internal oscillator
n TTL shutdown capability, low power standby mode
n High efficiency
n Uses readily available standard inductors
n Thermal shutdown and current limit protection
n P+ Product Enhancement tested
Other features include a guaranteed 4% tolerance on out-
put voltage within specified input voltages and output load
conditions, and 10% on the oscillator frequency. External
shutdown is included, featuring 50 µA (typical) standby cur-
rent. The output switch includes cycle-by-cycle current limit-
ing, as well as thermal shutdown for full protection under
fault conditions.
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)
n Selected Military Applications
n Selected Avionics Applications
Ordering Information
PART NUMBER
LM2575HVS-5.0EP
LM2575HVS-ADJEP
(Notes 1, 2)
VID PART NUMBER
NS PACKAGE NUMBER (Note 3)
V62/04742-01
V62/04742-02
TBD
TS5B
TS5B
TBD
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation
DS201132
www.national.com
Ordering Information (Continued)
Note 1: For the following (Enhanced Plastic) version, check for availability: LM2575M-12EP, LM2575M-15EP, LM2575M-3.3EP, LM2575M-5.0EP, LM2575M-
ADJEP, LM2575MX-12EP, LM2575MX-15EP, LM2575MX-3.3EP, LM2575MX-5.0EP, LM2575MX-ADJEP, LM2575N-12EP, LM2575N-15EP, LM2575N-5.0EP,
LM2575N-ADJEP, LM2575T-12EP, LM2575T-15EP, LM2575T-3.3EP, LM2575T-5.0EP, LM2575T-ADJEP, LM2575S-12EP, LM2575S-15EP, LM2575S-3.3EP,
LM2575S-5.0EP, LM2575S-ADJEP, LM2575SX-12EP, LM2575SX-15EP, LM2575SX-3.3EP, LM2575SX-5.0EP, LM2575SX-ADJEP, LM2575HVM-12EP,
LM2575HVM-15EP, LM2575HVM-5.0EP, LM2575HVM-ADJEP, LM2575HVMX-12EP, LM2575HVMX-15EP, LM2575HVMX-5.0EP, LM2575HVMX-ADJEP,
LM2575HVN-12EP, LM2575HVN-15EP, LM2575HVN-5.0EP, LM2575HVN-ADJEP, LM2575HVT-12EP, LM2575HVT-15EP, LM2575HVT-3.3EP, LM2575HVT-
5.0EP, LM2575HVT-ADJEP, LM2575HVS-12EP, LM2575HVS-15EP, LM2575HVS-3.3EP, LM2575HVSX-12EP, LM2575HVSX-15EP, LM2575HVSX-3.3EP,
LM2575HVSX-5.0EP, LM2575HVSX-ADJEP. Parts listed with an "X" are provided in Tape & Reel and parts without an "X" are in Rails.
Note 2: FOR ADDITIONAL ORDERING AND PRODUCT INFORMATION, PLEASE VISIT THE ENHANCED PLASTIC WEB SITE AT: www.national.com/mil
Note 3: Refer to package details under Physical Dimensions
Typical Application (Fixed Output Voltage
Versions)
20113201
Note: Pin numbers are for the TO-220 package.
Block Diagram and Typical Application
20113202
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 TO-220 package.
FIGURE 1.
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2
Connection Diagrams (XX indicates output voltage option. See Device Reference Information table for com-
plete part number.)
Straight Leads
5–Lead TO-22 (T)
Bent, Staggered Leads
5-Lead TO-220 (T)
20113224
20113222
20113223
Side View
See NS Package Number T05D
Top View
See NS Package Number T05A
Top View
16–Lead DIP (N)
24-Lead Surface Mount (M)
20113225
*No Internal Connection
Top ViewSee NS Package Number N16A
20113226
*No Internal Connection
Top View
See NS Package Number M24B
TO-263(S)
5-Lead Surface-Mount Package
20113229
Top View
20113230
Side View
See NS Package Number TS5B
3
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Device Reference Information
Package
NSC
Standard
Voltage Rating
(40V)
High
Voltage Rating
(60V)
Temperature
Range
Type
Package
Number
5-Lead TO-220
Straight Leads
T05A
LM2575T-3.3EP
LM2575HVT-3.3EP
LM2575T-5.0EP
LM2575T-12EP
LM2575T-15EP
LM2575T-ADJEP
LM2575HVT-5.0EP
LM2575HVT-12EP
LM2575HVT-15EP
LM2575HVT-ADJEP
5-Lead TO-220
Bent and
T05D
LM2575T-3.3EP Flow LB03 LM2575HVT-3.3EP Flow LB03
LM2575T-5.0EP Flow LB03 LM2575HVT-5.0EP Flow LB03
LM2575T-12EP Flow LB03 LM2575HVT-12EP Flow LB03
LM2575T-15EP Flow LB03 LM2575HVT-15EP Flow LB03
Staggered Leads
LM2575T-ADJEP Flow
LB03
LM2575HVT-ADJEP Flow LB03
16-Pin Molded
DIP
N16A
M24B
TS5B
LM2575N-5.0EP
LM2575N-12EP
LM2575N-15EP
LM2575N-ADJEP
LM2575M-5.0EP
LM2575M-12EP
LM2575M-15EP
LM2575M-ADJEP
LM2575S-3.3EP
LM2575S-5.0EP
LM2575S-12EP
LM2575S-15EP
LM2575S-ADJEP
LM2575HVN-5.0EP
LM2575HVN-12EP
LM2575HVN-15EP
LM2575HVN-ADJEP
LM2575HVM-5.0EP
LM2575HVM-12EP
LM2575HVM-15EP
LM2575HVM-ADJEP
LM2575HVS-3.3EP
LM2575HVS-5.0EP
LM2575HVS-12EP
LM2575HVS-15EP
LM2575HVS-ADJEP
−40˚C ≤ TJ ≤ +125˚C
24-Pin
Surface Mount
5-Lead TO-263
Surface Mount
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4
Absolute Maximum Ratings (Note 4)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Minimum ESD Rating
(C = 100 pF, R = 1.5 kΩ)
Lead Temperature
2 kV
(Soldering, 10 sec.)
260˚C
Maximum Supply Voltage
LM2575EP
45V
63V
Operating Ratings
LM2575HVEP
Temperature Range
LM2575EP/LM2575HVEP
Supply Voltage
ON /OFF Pin Input Voltage
Output Voltage to Ground
(Steady State)
−0.3V ≤ V ≤ +VIN
−40˚C ≤ TJ ≤ +125˚C
−1V
Internally Limited
−65˚C to +150˚C
150˚C
LM2575EP
40V
60V
Power Dissipation
LM2575HVEP
Storage Temperature Range
Maximum Junction Temperature
LM2575-3.3EP, LM2575HV-3.3EP
Electrical Characteristics (Note 16)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range .
Symbol
Parameter
Conditions
Typ
LM2575-3.3EP
LM2575HV-3.3EP
Limit
Units
(Limits)
(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 2
VOUT
VOUT
VOUT
η
Output Voltage
VIN = 12V, ILOAD = 0.2A
3.3
3.3
3.3
75
V
Circuit of Figure 2
3.234
3.366
V(Min)
V(Max)
V
Output Voltage
LM2575EP
4.75V ≤ VIN ≤ 40V, 0.2A ≤ ILOAD ≤ 1A
Circuit of Figure 2
3.168/3.135
3.432/3.465
V(Min)
V(Max)
V
Output Voltage
LM2575HVEP
4.75V ≤ VIN ≤ 60V, 0.2A ≤ ILOAD ≤ 1A
Circuit of Figure 2
3.168/3.135
3.450/3.482
V(Min)
V(Max)
%
Efficiency
VIN = 12V, ILOAD = 1A
LM2575-5.0EP, LM2575HV-5.0EP
Electrical Characteristics (Note 16)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range.
Symbol
Parameter
Conditions
Typ
LM2575-5.0EP
LM2575HV-5.0EP
Limit
Units
(Limits)
(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 2
VOUT
VOUT
VOUT
Output Voltage
VIN = 12V, ILOAD = 0.2A
5.0
5.0
5.0
V
Circuit of Figure 2
4.900
5.100
V(Min)
V(Max)
V
Output Voltage
LM2575EP
0.2A ≤ ILOAD ≤ 1A,
8V ≤ VIN ≤ 40V
4.800/4.750
5.200/5.250
V(Min)
V(Max)
V
Circuit of Figure 2
0.2A ≤ ILOAD ≤ 1A,
8V ≤ VIN ≤ 60V
Output Voltage
LM2575HVEP
4.800/4.750
5.225/5.275
V(Min)
V(Max)
Circuit of Figure 2
5
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LM2575-5.0EP, LM2575HV-5.0EP
Electrical Characteristics (Note 16) (Continued)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range.
Symbol
Parameter
Conditions
Typ
LM2575-5.0EP
LM2575HV-5.0EP
Limit
Units
(Limits)
(Note 5)
η
Efficiency
VIN = 12V, ILOAD = 1A
77
%
LM2575-12EP, LM2575HV-12EP
Electrical Characteristics (Note 16)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range .
Symbol
Parameter
Conditions
Typ
LM2575-12EP
LM2575HV-12EP
Limit
Units
(Limits)
(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 2
VOUT
VOUT
VOUT
η
Output Voltage
VIN = 25V, ILOAD = 0.2A
12
12
12
88
V
Circuit of Figure 2
11.76
12.24
V(Min)
V(Max)
V
Output Voltage
LM2575EP
0.2A ≤ ILOAD ≤ 1A,
15V ≤ VIN ≤ 40V
11.52/11.40
12.48/12.60
V(Min)
V(Max)
V
Circuit of Figure 2
0.2A ≤ ILOAD ≤ 1A,
15V ≤ VIN ≤ 60V
Output Voltage
LM2575HVEP
11.52/11.40
12.54/12.66
V(Min)
V(Max)
%
Circuit of Figure 2
VIN = 15V, ILOAD = 1A
Efficiency
LM2575-15EP, LM2575HV-15EP
Electrical Characteristics (Note 16)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture Range .
Symbol
Parameter
Conditions
Typ
LM2575-15EP
LM2575HV-15EP
Limit
Units
(Limits)
(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 2
VOUT
VOUT
VOUT
η
Output Voltage
VIN = 30V, ILOAD = 0.2A
15
15
15
88
V
Circuit of Figure 2
14.70
15.30
V(Min)
V(Max)
V
Output Voltage
LM2575EP
0.2A ≤ ILOAD ≤ 1A,
18V ≤ VIN ≤ 40V
14.40/14.25
15.60/15.75
V(Min)
V(Max)
V
Circuit of Figure 2
0.2A ≤ ILOAD ≤ 1A,
18V ≤ VIN ≤ 60V
Output Voltage
LM2575HVEP
14.40/14.25
15.68/15.83
V(Min)
V(Max)
%
Circuit of Figure 2
VIN = 18V, ILOAD = 1A
Efficiency
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6
LM2575-ADJEP, LM2575HV-ADJEP
Electrical Characteristics (Note 16)
Specifications with standard type face are for TJ= 25˚C, and those with boldface type apply over full Operating Temperature
Range.
Symbol
Parameter
Conditions
Typ
LM2575-ADJEP
LM2575HV-ADJEP
Limit
Units
(Limits)
(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 2
VOUT
VOUT
VOUT
η
Feedback Voltage
VIN = 12V, ILOAD = 0.2A
VOUT = 5V
1.230
1.230
1.230
77
V
1.217
1.243
V(Min)
V(Max)
V
Circuit of Figure 2
Feedback Voltage
LM2575EP
0.2A ≤ ILOAD ≤ 1A,
8V ≤ VIN ≤ 40V
1.193/1.180
1.267/1.280
V(Min)
V(Max)
V
VOUT = 5V, Circuit of Figure 2
0.2A ≤ ILOAD ≤ 1A,
Feedback Voltage
LM2575HVEP
8V ≤ VIN ≤ 60V
1.193/1.180
1.273/1.286
V(Min)
V(Max)
%
VOUT = 5V, Circuit of Figure 2
VIN = 12V, ILOAD = 1A, VOUT = 5V
Efficiency
All Output Voltage Versions
Electrical Characteristics (Note 16)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture 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 = 200 mA.
Symbol
Parameter
Conditions
Typ
LM2575-XXEP
LM2575HV-XXEP
Limit
Units
(Limits)
(Note 5)
DEVICE PARAMETERS
Ib
Feedback Bias Current
VOUT = 5V (Adjustable Version Only)
(Note 15)
50
52
100/500
nA
kHz
fO
Oscillator Frequency
47/42
58/63
kHz(Min)
kHz(Max)
V
VSAT
DC
Saturation Voltage
Max Duty Cycle (ON)
Current Limit
IOUT = 1A (Note 7)
(Note 8)
0.9
98
1.2/1.4
V(Max)
%
93
%(Min)
A
ICL
Peak Current (Notes 7, 15)
2.2
1.7/1.3
3.0/3.2
2
A(Min)
A(Max)
mA(Max)
mA
IL
Output Leakage
Current
(Notes 9, 10)
(Note 9)
Output = 0V
Output = −1V
Output = −1V
7.5
5
30
10
mA(Max)
mA
IQ
Quiescent Current
mA(Max)
µA
ISTBY
Standby Quiescent
Current
ON /OFF Pin = 5V (OFF)
50
200
µA(Max)
7
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All Output Voltage Versions
Electrical Characteristics (Note 16) (Continued)
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Tempera-
ture 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 = 200 mA.
Symbol
Parameter
Conditions
Typ
LM2575-XXEP
LM2575HV-XXEP
Limit
Units
(Limits)
(Note 5)
DEVICE PARAMETERS
θJA
Thermal Resistance
T Package, Junction to Ambient (Note 11)
T Package, Junction to Ambient (Note 12)
T Package, Junction to Case
65
45
2
θJA
˚C/W
θJC
θJA
N Package, Junction to Ambient (Note 13)
M Package, Junction to Ambient (Note 13)
S Package, Junction to Ambient (Note 14)
85
100
37
θJA
θJA
ON /OFF CONTROL Test Circuit Figure 2
VIH
VIL
IIH
ON /OFF Pin Logic
Input Level
VOUT = 0V
1.4
1.2
12
2.2/2.4
1.0/0.8
V(Min)
V(Max)
µA
VOUT = Nominal Output Voltage
ON /OFF Pin = 5V (OFF)
ON /OFF Pin Input
Current
30
µA(Max)
µA
IIL
ON /OFF Pin = 0V (ON)
0
10
µA(Max)
Note 4: 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 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100%
production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods.
Note 6: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the
LM2575EP is used as shown in the Figure 2 test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.
Note 7: Output (pin 2) sourcing current. No diode, inductor or capacitor connected to output pin.
Note 8: Feedback (pin 4) removed from output and connected to 0V.
Note 9: Feedback (pin 4) 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 10: V = 40V (60V for the high voltage version).
IN
1
Note 11: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with
⁄
2
inch leads in a socket, or on a
PC board with minimum copper area.
Note 12: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with 1
⁄
2
inch leads soldered to a PC board
containing approximately 4 square inches of copper area surrounding the leads.
Note 13: Junction to ambient thermal resistance with approximately 1 square inch of pc board copper surrounding the leads. Additional copper area will lower
thermal resistance further. See thermal model in Switchers made Simple software.
Note 14: If the TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package: Using
0.5 square inches of copper area, θ is 50˚C/W; with 1 square inch of copper area, θ is 37˚C/W; and with 1.6 or more square inches of copper area, θ is 32˚C/W.
JA
JA
JA
Note 15: 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%.
Note 16: "Testing and other quality control techniques are used to the extent deemed necessary to ensure product performance over the specified temperature
range. Product may not necessarily be tested across the full temperature range and all parameters may not necessarily be tested. In the absence of specific
PARAMETRIC testing, product performance is assured by characterization and/or design."
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Typical Performance Characteristics (Circuit of Figure 2)
Normalized Output Voltage
Line Regulation
Dropout Voltage
20113234
20113237
20113240
20113243
20113232
20113233
20113236
20113239
Standby
Quiescent Current
Current Limit
Quiescent Current
20113235
Switch Saturation
Voltage
Oscillator Frequency
Efficiency
20113238
Quiescent Current
vs Duty Cycle
Feedback Voltage
vs Duty Cycle
Minimum Operating Voltage
20113241
20113242
9
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Typical Performance Characteristics (Circuit of Figure 2) (Continued)
Maximum Power Dissipation
Feedback Pin Current
(TO-263) (See (Note 14))
20113228
20113205
Switching Waveforms
Load Transient Response
20113206
20113207
V
OUT
= 5V
A: Output Pin Voltage, 10V/div
B: Output Pin Current, 1A/div
C: Inductor Current, 0.5A/div
D: Output Ripple Voltage, 20 mV/div,
AC-Coupled
Horizontal Time Base: 5 µs/div
Single-point grounding (as indicated) or ground plane con-
struction should be used for best results. When using the
Adjustable version, physically locate the programming resis-
tors near the regulator, to keep the sensitive feedback wiring
short.
Test Circuit and Layout Guidelines
As in any switching regulator, layout is very important. Rap-
idly switching currents associated with wiring inductance
generate voltage transients which can cause problems. For
minimal inductance and ground loops, the length of the leads
indicated by heavy lines should be kept as short as possible.
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Test Circuit and Layout Guidelines (Continued)
Fixed Output Voltage Versions
20113208
C
C
— 100 µF, 75V, Aluminum Electrolytic
IN
— 330 µF, 25V, Aluminum Electrolytic
OUT
D1 — Schottky, 11DQ06
L1 — 330 µH, PE-52627 (for 5V in, 3.3V out, use 100 µH, PE-92108)
Adjustable Output Voltage Version
20113209
where V
= 1.23V, R1 between 1k and 5k.
REF
R1 — 2k, 0.1%
R2 — 6.12k, 0.1%
Note: Pin numbers are for the TO-220 package.
FIGURE 2.
11
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LM2575EP Series Buck Regulator Design Procedure
PROCEDURE (Fixed Output Voltage Versions)
Given: VOUT = Regulated Output Voltage (3.3V, 5V, 12V, or
15V) VIN(Max) = Maximum Input Voltage ILOAD(Max) =
Maximum Load Current
EXAMPLE (Fixed Output Voltage Versions)
Given: VOUT = 5V VIN(Max) = 20V ILOAD(Max) = 0.8A
1. Inductor Selection (L1) A. Select the correct Inductor
value selection guide from Figures 3, 4, 5, 6 (Output
voltages of 3.3V, 5V, 12V or 15V respectively). For other
output voltages, see the design procedure for the adjustable
version. B. From the inductor value selection guide, identify
the inductance region intersected by VIN(Max) and
ILOAD(Max), and note the inductor code for that region. C.
Identify the inductor value from the inductor code, and
select an appropriate inductor from the table shown in
Figure 9. Part numbers are listed for three inductor
manufacturers. The inductor chosen must be rated for
operation at the LM2575EP switching frequency (52 kHz)
and for a current rating of 1.15 x ILOAD. For additional
inductor information, see the inductor section in the
Application Hints section of this data sheet.
1. Inductor Selection (L1) A. Use the selection guide
shown in Figure 4. B. From the selection guide, the
inductance area intersected by the 20V line and 0.8A line is
L330. C. Inductor value required is 330 µH. From the table
in Figure 9, choose AIE 415-0926, Pulse Engineering
PE-52627, or RL1952.
2. 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 and an acceptable output ripple voltage,
(approximately 1% of the output voltage) a value between
100 µF and 470 µF is recommended. B. The capacitor’s
voltage rating should be at least 1.5 times greater than the
output voltage. For a 5V regulator, a rating of at least 8V is
appropriate, and a 10V or 15V rating is recommended.
Higher voltage electrolytic capacitors generally have lower
ESR numbers, and for this reason it may be necessary to
select a capacitor rated for a higher voltage than would
normally be needed.
2. Output Capacitor Selection (COUT) A. COUT = 100 µF
to 470 µF standard aluminum electrolytic. B. Capacitor
voltage rating = 20V.
3. Catch Diode Selection (D1) A. The catch-diode current
rating must be at least 1.2 times greater than the maximum
load current. Also, if the power supply design must
withstand a continuous output short, the diode should have
a current rating equal to the maximum current limit of the
LM2575EP. The most stressful condition for this diode is an
overload or shorted output condition. B. The reverse voltage
rating of the diode should be at least 1.25 times the
maximum input voltage.
3. Catch Diode Selection (D1) A. For this example, a 1A
current rating is adequate. B. Use a 30V 1N5818 or SR103
Schottky diode, or any of the suggested fast-recovery
diodes shown in Figure 8.
4. Input Capacitor (CIN) An aluminum or tantalum
electrolytic bypass capacitor located close to the regulator is
needed for stable operation.
4. Input Capacitor (CIN) A 47 µF, 25V aluminum electrolytic
capacitor located near the input and ground pins provides
sufficient bypassing.
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12
Inductor Value Selection Guides (For Continuous Mode Operation)
20113212
20113210
FIGURE 5. LM2575(HV)-12EP
FIGURE 3. LM2575(HV)-3.3EP
20113213
20113211
FIGURE 6. LM2575(HV)-15EP
FIGURE 4. LM2575(HV)-5.0EP
20113214
FIGURE 7. LM2575(HV)-ADJEP
13
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Inductor Value Selection Guides (For Continuous Mode Operation) (Continued)
PROCEDURE (Adjustable Output Voltage Versions)
Given: VOUT = Regulated Output Voltage VIN(Max) =
Maximum Input Voltage ILOAD(Max) = Maximum Load
Current F = Switching Frequency (Fixed at 52 kHz)
1. Programming Output Voltage (Selecting R1 and R2, as
shown in Figure 2 ) Use the following formula to select the
appropriate resistor values.
EXAMPLE (Adjustable Output Voltage Versions)
Given: VOUT = 10V VIN(Max) = 25V ILOAD(Max) = 1A F =
52 kHz
1.Programming Output Voltage (Selecting R1 and R2)
R1 can be between 1k and 5k. (For best temperature coef-
ficient and stability with time, use 1% metal film resistors)
R2 = 1k (8.13 − 1) = 7.13k, closest 1% value is 7.15k
2. Inductor Selection (L1) A. Calculate the inductor Volt •
microsecond constant, E • T (V • µs), from the following
formula:
2. Inductor Selection (L1) A. Calculate E • T (V • µs)
B. E • T = 115 V • µs C. ILOAD(Max) = 1A D. Inductance
Region = H470 E. Inductor Value = 470 µH Choose from AIE
part #430-0634, Pulse Engineering part #PE-53118, or
Renco part #RL-1961.
B. Use the E • T value from the previous formula and match
it with the E • T number on the vertical axis of the Inductor
Value Selection Guide shown in Figure 7. C. On the hori-
zontal 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 code for
that region. E. Identify the inductor value from the inductor
code, and select an appropriate inductor from the table shown
in Figure 9. Part numbers are listed for three inductor manu-
facturers. The inductor chosen must be rated for operation at
the LM2575EP switching frequency (52 kHz) and for a current
rating of 1.15 x ILOAD. For additional inductor information, see
the inductor section in the application hints section of this data
sheet.
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
requirement:
3. Output Capacitor Selection (COUT) A.
However, for acceptable output ripple voltage select COUT
220 µF COUT = 220 µF electrolytic capacitor
≥
The above formula yields capacitor values between 10 µF
and 2000 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 re-
sponse, the output capacitor may need to be several times
larger than the above formula yields. B. The capacitor’s volt-
age 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 gen-
erally 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) A. The catch-diode current
rating must be at least 1.2 times greater than the maximum
load current. Also, if the power supply design must
4. Catch Diode Selection (D1) A. For this example, a 3A
current rating is adequate. B. Use a 40V MBR340 or
31DQ04 Schottky diode, or any of the suggested
fast-recovery diodes in Figure 8.
withstand a continuous output short, the diode should have
a current rating equal to the maximum current limit of the
LM2575EP. The most stressful condition for this diode is an
overload or shorted output. See diode selection guide in
Figure 8. B. The reverse voltage rating of the diode should
be at least 1.25 times the maximum input voltage.
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14
Inductor Value Selection Guides (For Continuous Mode Operation) (Continued)
PROCEDURE (Adjustable Output Voltage Versions)
5. Input Capacitor (CIN) An aluminum or tantalum
electrolytic bypass capacitor located close to the regulator is
needed for stable operation.
EXAMPLE (Adjustable Output Voltage Versions)
5. Input Capacitor (CIN) A 100 µF aluminum electrolytic
capacitor located near the input and ground pins provides
sufficient bypassing.
To further simplify the buck regulator design procedure, National Semiconductor is making available computer design software to
be used with the Simple Switcher line of switching regulators. Switchers Made Simple (version 3.3) is available on a (31⁄
")
2
diskette for IBM compatible computers from a National Semiconductor sales office in your area.
15
www.national.com
Inductor Value Selection Guides (For Continuous Mode Operation) (Continued)
VR
Schottky
Fast Recovery
1A 3A
1A
3A
1N5820
20V 1N5817
MBR120P
SR102
MBR320
SR302
30V 1N5818
MBR130P
11DQ03
1N5821
MBR330
31DQ03
SR303
The following The following
diodes are all diodes are all
rated to 100V rated to 100V
SR103
40V 1N5819
MBR140P
11DQ04
IN5822
MBR340
31DQ04
SR304
11DF1
MUR110
HER102
31DF1
MURD310
HER302
SR104
50V MBR150
11DQ05
MBR350
31DQ05
SR305
SR105
60V MBR160
11DQ06
MBR360
31DQ06
SR306
SR106
FIGURE 8. Diode Selection Guide
Inductor
Code
Inductor
Value
Schott
Pulse Eng.
(Note 18)
PE-92108
PE-53113
PE-52626
PE-52627
PE-53114
PE-52629
PE-53115
PE-53116
PE-53117
PE-53118
PE-53119
PE-53120
PE-53121
PE-53122
Renco
(Note 19)
RL2444
RL1954
RL1953
RL1952
RL1951
RL1950
RL2445
RL2446
RL2447
RL1961
RL1960
RL1959
RL1958
RL2448
(Note 17)
L100
L150
L220
L330
L470
L680
H150
H220
H330
H470
H680
H1000
H1500
H2200
100 µH
150 µH
67127000
67127010
67127020
67127030
67127040
67127050
67127060
67127070
67127080
67127090
67127100
67127110
67127120
67127130
220 µH
330 µH
470 µH
680 µH
150 µH
220 µH
330 µH
470 µH
680 µH
1000 µH
1500 µH
2200 µH
Note 17: Schott Corp., (612) 475-1173, 1000 Parkers Lake Rd., Wayzata, MN 55391.
Note 18: Pulse Engineering, (619) 674-8100, P.O. Box 12236, San Diego, CA 92112.
Note 19: Renco Electronics Inc., (516) 586-5566, 60 Jeffryn Blvd. East, Deer Park, NY 11729.
FIGURE 9. Inductor Selection by Manufacturer’s Part Number
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16
pletely contained within the core, it generates more electro-
magnetic interference (EMI). This EMI can cause problems
in sensitive circuits, or can give incorrect scope readings
because of induced voltages in the scope probe.
Application Hints
INPUT CAPACITOR (CIN
)
To maintain stability, the regulator input pin must be by-
passed with at least a 47 µF electrolytic capacitor. The
capacitor’s leads must be kept short, and located near the
regulator.
The inductors listed in the selection chart include ferrite pot
core construction for AIE, powdered iron toroid for Pulse
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 will cause the switch current to rise very
rapidly. Different inductor types have different saturation
characteristics, and this should be kept in mind when select-
ing an inductor.
If the operating temperature range includes temperatures
below −25˚C, the input capacitor value may need to be
larger. With most electrolytic capacitors, the capacitance
value decreases and the ESR increases with lower tempera-
tures and age. Paralleling a ceramic or solid tantalum ca-
pacitor will increase the regulator stability at cold tempera-
tures. For maximum capacitor operating lifetime, the
capacitor’s RMS ripple current rating should be greater than
The inductor manufacturer’s data sheets include current and
energy limits to avoid inductor saturation.
INDUCTOR RIPPLE CURRENT
When the switcher is operating in the continuous mode, the
inductor current waveform ranges from a triangular to a
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 saw-
tooth current waveform also rises or falls. The average DC
value of this waveform is equal to the DC load current (in the
buck regulator configuration).
INDUCTOR SELECTION
All switching regulators have two basic modes of operation:
continuous and discontinuous. The difference between the
two types relates to the inductor current, whether it is flowing
continuously, or if it drops to zero for a period of time in the
normal switching cycle. Each mode has distinctively different
operating characteristics, which can affect the regulator per-
formance and requirements.
If the load current drops to a low enough level, the bottom of
the sawtooth current waveform will reach zero, and the
switcher will change to a discontinuous mode of operation.
This is a perfectly acceptable mode of operation. Any buck
switching regulator (no matter how large the inductor value
is) will be forced to run discontinuous if the load current is
light enough.
The LM2575EP (or any of the Simple Switcher family) can
be used for both continuous and discontinuous modes of
operation.
OUTPUT CAPACITOR
An output capacitor is required to filter the output voltage and
is needed for loop stability. The capacitor should be located
near the LM2575EP 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, physi-
cal size and the type of construction. In general, low value or
low voltage (less than 12V) electrolytic capacitors usually
have higher ESR numbers.
The inductor value selection guides in Figure 3 through
Figure 7 were designed for buck regulator designs of the
continuous inductor current type. When using inductor val-
ues shown in the inductor selection guide, the peak-to-peak
inductor ripple current will be approximately 20% to 30% of
the maximum DC current. With relatively heavy load cur-
rents, the circuit operates in the continuous mode (inductor
current always flowing), but under light load conditions, the
circuit will be forced to the discontinuous mode (inductor
current falls to zero for a period of time). This discontinuous
mode of operation is perfectly acceptable. For light loads
(less than approximately 200 mA) it may be desirable to
operate the regulator in the discontinuous mode, primarily
because of the lower inductor values required for the discon-
tinuous mode.
The amount of output ripple voltage is primarily a function of
the ESR (Equivalent Series Resistance) of the output ca-
pacitor and the amplitude of the inductor ripple current
(∆IIND). See the section on inductor ripple current in Applica-
tion Hints.
The lower capacitor values (220 µF–680 µF) will allow typi-
cally 50 mV to 150 mV of output ripple voltage, while larger-
value capacitors will reduce the ripple to approximately 20
mV to 50 mV.
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.
Output Ripple Voltage = (∆IIND) (ESR of COUT
)
To further reduce the output ripple voltage, several standard
electrolytic capacitors may be paralleled, or a higher-grade
capacitor may be used. Such capacitors are often called
“high-frequency,” “low-inductance,” or “low-ESR.” These will
reduce the output ripple to 10 mV or 20 mV. However, when
operating in the continuous mode, reducing the ESR below
0.05Ω can cause instability in the regulator.
Inductors are available in different styles such as pot core,
toriod, E-frame, bobbin core, etc., as well as different core
materials, such as ferrites and powdered iron. The least
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 com-
17
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high-level TTL or CMOS signal. The ON /OFF pin can be
safely pulled up to +VIN without a resistor in series with it.
The ON /OFF pin should not be left open.
Application Hints (Continued)
Tantalum capacitors can have a very low ESR, and should
be carefully evaluated if it is the only output capacitor. Be-
cause of their good low temperature characteristics, a tan-
talum can be used in parallel with aluminum electrolytics,
with the tantalum making up 10% or 20% of the total capaci-
tance.
GROUNDING
To maintain output voltage stability, the power ground con-
nections must be low-impedance (see Figure 2). For the
TO-3 style package, the case is ground. For the 5-lead
TO-220 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.
The capacitor’s ripple current rating at 52 kHz should be at
least 50% higher than the peak-to-peak inductor ripple cur-
rent.
With the N or M packages, all the pins labeled ground, power
ground, or signal ground should be soldered directly to wide
printed circuit board copper traces. This assures both low
inductance connections and good thermal properties.
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 LM2575EP using short leads and
short printed circuit traces.
HEAT SINK/THERMAL CONSIDERATIONS
In many cases, no heat sink is required to keep the
LM2575EP junction temperature within the allowed operat-
ing range. For each application, to determine whether or not
a heat sink will be required, the following must be identified:
Because of their fast switching speed and low forward volt-
age drop, Schottky diodes provide the best efficiency, espe-
cially in low output voltage switching regulators (less than
5V). Fast-Recovery, High-Efficiency, or Ultra-Fast Recovery
diodes are also suitable, but some types with an abrupt
turn-off characteristic may cause instability and EMI prob-
lems. A fast-recovery diode with soft recovery characteristics
is a better choice. Standard 60 Hz diodes (e.g., 1N4001 or
1N5400, etc.) are also not suitable. See Figure 8 for Schot-
tky and “soft” fast-recovery diode selection guide.
1. Maximum ambient temperature (in the application).
2. Maximum regulator power dissipation (in application).
3. Maximum allowed junction temperature (125˚C for the
LM2575EP). For a safe, conservative design, a tem-
perature approximately 15˚C cooler than the maximum
temperature should be selected.
4. LM2575EP package thermal resistances θJA and θJC
.
OUTPUT VOLTAGE RIPPLE AND TRANSIENTS
Total power dissipated by the LM2575EP can be estimated
as follows:
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.
PD = (VIN) (IQ) + (VO/VIN) (ILOAD) (VSAT
)
where IQ (quiescent current) and VSAT can be found in the
Characteristic Curves shown previously, VIN is the applied
minimum input voltage, VO is the regulated output voltage,
and ILOAD is the load current. The dynamic losses during
turn-on and turn-off are negligible if a Schottky type catch
diode is used.
The output ripple voltage is due mainly to the inductor saw-
tooth 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 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.
When no heat sink is used, the junction temperature rise can
be determined by the following:
∆TJ = (PD) (θJA
)
To arrive at the actual operating junction temperature, add
the junction temperature rise to the maximum ambient tem-
perature.
TJ = ∆TJ + TA
An additional small LC filter (20 µH & 100 µF) can be added
to the output (as shown in Figure 15) to further reduce the
amount of output ripple and transients. A 10 x reduction in
output ripple voltage and transients is possible with this filter.
If the actual operating junction temperature is greater than
the selected safe operating junction temperature determined
in step 3, then a heat sink is required.
When using a heat sink, the junction temperature rise can be
determined by the following:
FEEDBACK CONNECTION
The LM2575EP (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 LM2575
to avoid picking up unwanted noise. Avoid using resistors
greater than 100 kΩ because of the increased chance of
noise pickup.
∆TJ = (PD) (θJC + θinterface + θHeat sink
The operating junction temperature will be:
TJ = TA + ∆TJ
As above, if the actual operating junction temperature is
greater than the selected safe operating junction tempera-
ture, then a larger heat sink is required (one that has a lower
thermal resistance).
)
ON /OFF INPUT
When using the LM2575EP in the plastic DIP (N) or surface
mount (M) packages, several items about the thermal prop-
erties of the packages should be understood. The majority of
the heat is conducted out of the package through the leads,
with a minor portion through the plastic parts of the package.
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
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18
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 1.5A. Using a delayed
turn-on or an undervoltage lockout circuit (described in the
next section) would allow the input voltage to rise to a high
enough level before the switcher would be allowed to turn
on.
Application Hints (Continued)
Since the lead frame is solid copper, heat from the die is
readily conducted through the leads to the printed circuit
board copper, which is acting as a heat sink.
For best thermal performance, the ground pins and all the
unconnected 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 to the
surrounding air. Copper on both sides of the board is also
helpful in getting the heat away from the package, even if
there is no direct copper contact between the two sides.
Thermal resistance numbers as low as 40˚C/W for the SO
package, and 30˚C/W for the N package can be realized with
a carefully engineered pc board.
Because of the structural differences between the buck and
the buck-boost regulator topologies, the buck regulator de-
sign procedure section can not be used to 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).
Included on the Switchers Made Simple design software is
a more precise (non-linear) thermal model that can be used
to determine junction temperature with different input-output
parameters or different component values. It can also calcu-
late the heat sink thermal resistance required to maintain the
regulators junction temperature below the maximum operat-
ing temperature.
The peak inductor current, which is the same as the peak
switch current, can be calculated from the following formula:
Additional Applications
Where fosc = 52 kHz. 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.
INVERTING REGULATOR
Figure 10 shows a LM2575-12EP in a buck-boost configu-
ration 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 volt-
age and regulates it to −12V.
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 LM2575EP is
+28V, or +48V for the LM2575HVEP.
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.
For an input voltage of 12V or more, the maximum available
output current in this configuration is approximately 0.35A. 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
20113215
FIGURE 10. Inverting Buck-Boost Develops −12V
NEGATIVE BOOST REGULATOR
Because of the boosting function of this type of regulator, the
switch current is relatively high, especially at low input volt-
ages. Output load current limitations are a result of the
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.
Another variation on the buck-boost topology is the negative
boost configuration. The circuit in Figure 11 accepts an input
voltage ranging from −5V to −12V and provides a regulated
−12V output. Input voltages greater than −12V will cause the
output to rise above −12V, but will not damage the regulator.
19
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Additional Applications (Continued)
20113217
20113216
Note: Complete circuit not shown.
Typical Load Current
Note: Pin numbers are for the TO-220 package.
200 mA for V = −5.2V
IN
500 mA for V = −7V
IN
Note: Pin numbers are for TO-220 package.
FIGURE 12. Undervoltage Lockout for Buck Circuit
FIGURE 11. Negative Boost
UNDERVOLTAGE LOCKOUT
In some applications it is desirable to keep the regulator off
until the input voltage reaches a certain threshold. An und-
ervoltage lockout circuit which accomplishes this task is
shown in Figure 12, while Figure 13 shows the same circuit
applied to a buck-boost configuration. These circuits keep
the regulator off until the input voltage reaches a predeter-
mined level.
VTH ≈ VZ1 + 2VBE (Q1)
20113218
DELAYED STARTUP
Note: Complete circuit not shown (see Figure 10).
The ON /OFF pin can be used to provide a delayed startup
feature as shown in Figure 14. With an input voltage of 20V
and for the part values shown, the circuit provides approxi-
mately 10 ms of delay time before the circuit begins switch-
ing. 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.
Note: Pin numbers are for the TO-220 package.
FIGURE 13. Undervoltage Lockout
for Buck-Boost Circuit
ADJUSTABLE OUTPUT, LOW-RIPPLE
POWER SUPPLY
A 1A power supply that features an adjustable output voltage
is shown in Figure 15. An additional L-C filter that reduces
the output ripple by a factor of 10 or more is included in this
circuit.
20113219
Note: Complete circuit not shown.
Note: Pin numbers are for the TO-220 package.
FIGURE 14. Delayed Startup
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20
Additional Applications (Continued)
20113220
Note: Pin numbers are for the TO-220 package.
FIGURE 15. 1.2V to 55V Adjustable 1A Power Supply with Low Output Ripple
Definition of Terms
BUCK REGULATOR
20113221
A switching regulator topology in which a higher voltage is
converted to a lower voltage. Also known as a step-down
switching regulator.
FIGURE 16. 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 “low-
inductance”’) in the 100 µF–1000 µF range generally have
ESR of less than 0.15Ω.
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.
EQUIVALENT SERIES INDUCTANCE (ESL)
The pure inductance component of a capacitor (see Figure
16). 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 volt-
age. It is usually dominated by the output capacitor’s ESR
multiplied by the inductor’s ripple current (∆IIND). The peak-
to-peak value of this sawtooth ripple current can be deter-
mined by reading the Inductor Ripple Current section of the
Application hints.
CATCH DIODE OR CURRENT STEERING DIODE
The diode which provides a return path for the load current
when the LM2575EP switch is OFF.
EFFICIENCY (η)
The proportion of input power actually delivered to the load.
CAPACITOR RIPPLE CURRENT
RMS value of the maximum allowable alternating current at
which a capacitor can be operated continuously at a speci-
fied temperature.
STANDBY QUIESCENT CURRENT (ISTBY
)
CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)
Supply current required by the LM2575EP when in the
standby mode (ON /OFF pin is driven to TTL-high voltage,
thus turning the output switch OFF).
The purely resistive component of a real capacitor’s imped-
ance (see Figure 16). It causes power loss resulting in
capacitor heating, which directly affects the capacitor’s op-
erating lifetime. When used as a switching regulator output
filter, higher ESR values result in higher output ripple volt-
ages.
INDUCTOR RIPPLE CURRENT (∆IIND
)
The peak-to-peak value of the inductor current waveform,
typically a sawtooth waveform when the regulator is operat-
ing in the continuous mode (vs. discontinuous mode).
21
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nates. Inductor current is then limited only by the DC resis-
tance of the wire and the available source current.
Definition of Terms (Continued)
CONTINUOUS/DISCONTINUOUS MODE OPERATION
OPERATING VOLT MICROSECOND CONSTANT (E•Top
)
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.
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.
INDUCTOR SATURATION
The condition which exists when an inductor cannot hold any
more magnetic flux. When an inductor saturates, the induc-
tor appears less inductive and the resistive component domi-
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22
Physical Dimensions inches (millimeters)
unless otherwise noted
24-Lead Molded Package
NS Package Number M24B
16-Lead Molded DIP (N)
NS Package Number N16A
23
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
5-Lead TO-220 (T)
NS Package Number T05A
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24
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
TO-263, Molded, 5-Lead Surface Mount
NS Package Number TS5B
25
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Bent, Staggered 5-Lead TO-220 (T)
NS Package Number T05D
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For the most current product information visit us at www.national.com.
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in a significant injury to the user.
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device or system whose failure to perform can be reasonably
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