LM2574-15MWC
更新时间:2024-09-18 18:52:59
品牌:NSC
描述:IC 1.8 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, UUC, WAFER, Switching Regulator or Controller
LM2574-15MWC 概述
IC 1.8 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, UUC, WAFER, Switching Regulator or Controller 开关式稳压器或控制器
LM2574-15MWC 规格参数
生命周期: | Transferred | 包装说明: | DIE, WAFER |
Reach Compliance Code: | unknown | ECCN代码: | EAR99 |
HTS代码: | 8542.39.00.01 | 风险等级: | 5.55 |
模拟集成电路 - 其他类型: | SWITCHING REGULATOR | 控制模式: | VOLTAGE-MODE |
最大输入电压: | 40 V | 最小输入电压: | 18 V |
标称输入电压: | 30 V | JESD-30 代码: | X-XUUC-N |
功能数量: | 1 | 最高工作温度: | 125 °C |
最低工作温度: | -40 °C | 最大输出电流: | 1.8 A |
封装主体材料: | UNSPECIFIED | 封装代码: | DIE |
封装等效代码: | WAFER | 封装形状: | UNSPECIFIED |
封装形式: | UNCASED CHIP | 认证状态: | Not Qualified |
子类别: | Switching Regulator or Controllers | 表面贴装: | YES |
切换器配置: | BUCK | 最大切换频率: | 63 kHz |
技术: | BIPOLAR | 温度等级: | AUTOMOTIVE |
端子形式: | NO LEAD | 端子位置: | UPPER |
Base Number Matches: | 1 |
LM2574-15MWC 数据手册
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June 1999
LM2574/LM2574HV
™
SIMPLE SWITCHER 0.5A Step-Down Voltage Regulator
General Description
Features
n 3.3V, 5V, 12V, 15V, and adjustable output versions
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.
n Adjustable version output voltage range, 1.23V to 37V
(57V for HV version) 4% max over line and load
conditions
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
±
Requiring a minimum number 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.
n Uses readily available standard inductors
n Thermal shutdown and current limit protection
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.
Applications
n Simple high-efficiency step-down (buck) regulator
n Efficient pre-regulator for linear regulators
n On-card switching regulators
±
Other features include a guaranteed 4% tolerance on out-
n Positive to negative converter (Buck-Boost)
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.
Typical Application (Fixed Output Voltage Versions)
DS011394-1
Note: Pin numbers are for 8-pin DIP package.
Patent Pending
™
SIMPLE SWITCHER is a trademark of National Semiconductor Corporation
© 1999 National Semiconductor Corporation
DS011394
www.national.com
Connection Diagrams
8-Lead DIP
14-Lead Wide
Surface Mount (WM)
DS011394-2
* No internal connection, but should be soldered to PC board for best heat
transfer.
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
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 N08A
See NS Package Number M14B
www.national.com
2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Lead Temperature
(Soldering, 10 seconds)
Maximum Junction Temperature
Power Dissipation
260˚C
150˚C
Internally Limited
Maximum Supply Voltage
Operating Ratings
LM2574
45V
63V
LM2574HV
Temperature Range
LM2574/LM2574HV
Supply Voltage
LM2574
ON /OFF Pin Input Voltage
Output Voltage to Ground
(Steady State)
−0.3V ≤ V ≤ +VIN
−40˚C ≤ TJ ≤ +125˚C
−1V
40V
60V
Minimum ESD Rating
LM2574HV
=
=
(C 100 pF, R 1.5 kΩ)
2 kV
Storage Temperature Range
−65˚C to +150˚C
LM2574-3.3, LM2574HV-3.3
Electrical Characteristics
=
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
LM2574-3.3
LM2574HV-3.3
Limit
Units
(Limits)
Typ
3.3
3.3
3.3
72
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
=
=
VOUT
VOUT
VOUT
η
Output Voltage
VIN 12V, ILOAD 100 mA
V
3.234
3.366
V(Min)
V(Max)
V
Output Voltage
LM2574
4.75V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.5A
4.75V ≤ VIN ≤ 60V, 0.1A ≤ ILOAD ≤ 0.5A
3.168/3.135
3.432/3.465
V(Min)
V(Max)
Output Voltage
LM2574HV
3.168/3.135
3.450/3.482
V(Min)
V(Max)
%
= =
VIN 12V, ILOAD 0.5A
Efficiency
LM2574-5.0, LM2574HV-5.0
Electrical Characteristics
=
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
LM2574-5.0
LM2574HV-5.0
Limit
Units
(Limits)
Typ
5
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
=
=
VOUT
VOUT
VOUT
η
Output Voltage
VIN 12V, ILOAD 100 mA
V
4.900
5.100
V(Min)
V(Max)
V
Output Voltage
LM2574
7V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.5A
7V ≤ VIN ≤ 60V, 0.1A ≤ ILOAD ≤ 0.5A
5
4.800/4.750
5.200/5.250
V(Min)
V(Max)
Output Voltage
LM2574HV
5
4.800/4.750
5.225/5.275
V(Min)
V(Max)
%
=
=
Efficiency
VIN 12V, ILOAD 0.5A
77
3
www.national.com
LM2574-12, LM2574HV-12
Electrical Characteristics
=
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
LM2574-12
LM2574HV-12
Limit
Units
(Limits)
Typ
12
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
=
=
VOUT
VOUT
VOUT
η
Output Voltage
VIN 25V, ILOAD 100 mA
V
11.76
12.24
V(Min)
V(Max)
V
Output Voltage
LM2574
15V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.5A
15V ≤ VIN ≤ 60V, 0.1A ≤ ILOAD ≤ 0.5A
12
11.52/11.40
12.48/12.60
V(Min)
V(Max)
Output Voltage
LM2574HV
12
11.52/11.40
12.54/12.66
V(Min)
V(Max)
%
=
=
Efficiency
VIN 15V, ILOAD 0.5A
88
LM2574-15, LM2574HV-15
Electrical Characteristics
=
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
LM2574-15
LM2574HV-15
Limit
Units
(Limits)
Typ
15
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
=
=
VOUT
VOUT
VOUT
η
Output Voltage
VIN 30V, ILOAD 100 mA
V
14.70
15.30
V(Min)
V(Max)
V
Output Voltage
LM2574
18V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.5A
18V ≤ VIN ≤ 60V, 0.1A ≤ ILOAD ≤ 0.5A
15
14.40/14.25
15.60/15.75
V(Min)
V(Max)
Output Voltage
LM2574HV
15
14.40/14.25
15.68/15.83
V(Min)
V(Max)
%
=
=
Efficiency
VIN 18V, ILOAD 0.5A
88
LM2574-ADJ, LM2574HV-ADJ
Electrical Characteristics
=
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, ILOAD 100 mA.
Symbol Parameter Conditions
LM2574-ADJ
Units
(Limits)
LM2574HV-ADJ
Typ
Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
=
=
VFB
Feedback Voltage
VIN 12V, ILOAD 100 mA
1.230
V
1.217
1.243
V(Min)
V(Max)
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4
LM2574-ADJ, LM2574HV-ADJ
Electrical Characteristics (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, ILOAD 100 mA.
Symbol Parameter Conditions
LM2574-ADJ
Units
(Limits)
LM2574HV-ADJ
Typ
Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
VFB
VFB
η
Feedback Voltage
LM2574
7V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 0.5A
1.230
1.230
77
V
VOUT Programmed for 5V. Circuit of Figure 2
1.193/1.180
1.267/1.280
V(Min)
V(Max)
Feedback Voltage
LM2574HV
7V ≤ VIN ≤ 60V, 0.1A ≤ ILOAD ≤ 0.5A
VOUT Programmed for 5V. Circuit of Figure 2
1.193/1.180
1.273/1.286
V(Min)
V(Max)
%
= = =
VIN 12V, VOUT 5V, ILOAD 0.5A
Efficiency
All Output Voltage Versions
Electrical Characteristics
=
Specifications with standard type face are for TJ 25˚C, and those with boldface type apply over full Operating 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 100 mA.
Symbol Parameter Conditions
LM2574-XX
LM2574HV-XX
Limit
Units
(Limits)
Typ
(Note 2)
DEVICE PARAMETERS
=
Ib
Feedback Bias
Current
Adjustable Version Only, VOUT 5V
50
52
100/500
nA
fO
Oscillator Frequency
Saturation Voltage
(see Note 10)
kHz
kHz(Min)
kHz(Max)
V
47/42
58/63
=
VSAT
DC
IOUT 0.5A (Note 4)
0.9
98
1.2/1.4
V(max)
%
Max Duty Cycle
(ON)
(Note 5)
93
%(Min)
A
ICL
Current Limit
Peak Current, (Notes 4, 10)
1.0
0.7/0.65
1.6/1.8
2
A(Min)
A(Max)
mA(Max)
mA
=
Output 0V
IL
Output Leakage
Current
(Notes 6, 7)
(Note 6)
=
Output −1V
7.5
5
=
Output −1V
30
10
mA(Max)
mA
IQ
Quiescent Current
mA(Max)
µA
=
ISTBY
Standby Quiescent
Current
ON /OFF Pin 5V (OFF)
50
200
µA(Max)
θJA
θJA
θJA
θJA
Thermal Resistance
N Package, Junction to Ambient (Note 8)
N Package, Junction to Ambient (Note 9)
M Package, Junction to Ambient (Note 8)
M Package, Junction to Ambient (Note 9)
92
72
˚C/W
102
78
5
www.national.com
All Output Voltage Versions
Electrical Characteristics (Continued)
=
Specifications with standard type face are for TJ 25˚C, and those with boldface type apply over full Operating 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 100 mA.
=
=
Symbol Parameter Conditions
LM2574-XX
LM2574HV-XX
Limit
Units
(Limits)
Typ
(Note 2)
ON /OFF CONTROL Test Circuit Figure 2
=
VIH
VIL
IH
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
10
µA(Max)
µA
=
IIL
ON /OFF Pin 0V (ON)
0
µA(Max)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is in-
tended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: All limits guaranteed at room temperature (Standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% produc-
tion tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. 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 Figure 2 test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.
Note 4: Output pin sourcing current. No diode, inductor or capacitor connected to output 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.
=
40V (60V for high voltage version).
Note 7:
V
IN
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%.
Typical Performance Characteristics (Circuit of Figure 2)
Normalized Output Voltage
Line Regulation
Dropout Voltage
DS011394-27
DS011394-28
DS011394-29
www.national.com
6
Typical Performance Characteristics (Circuit of Figure 2) (Continued)
Current Limit
Supply Current
Standby
Quiescent Current
DS011394-30
DS011394-31
DS011394-32
Oscillator Frequency
Switch Saturation
Voltage
Efficiency
DS011394-33
DS011394-35
DS011394-34
Minimum Operating Voltage
Supply Current
vs Duty Cycle
Feedback Voltage
vs Duty Cycle
DS011394-36
DS011394-37
DS011394-38
7
www.national.com
Typical Performance Characteristics (Circuit of Figure 2) (Continued)
Feedback
Pin Current
Junction to Ambient
Thermal Resistance
DS011394-40
DS011394-39
Continuous Mode Switching Waveforms
Discontinuous Mode Switching Waveforms
=
=
VOUT 5V, 500 mA Load Current, L 330 µH
=
=
VOUT 5V, 100 mA Load Current, L 100 µH
DS011394-6
DS011394-7
Notes:
Notes:
A: Output Pin Voltage, 10V/div
B: Inductor Current, 0.2 A/div
C: Output Ripple Voltage, 20 mV/div,
AC-Coupled
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
Horizontal Time Base: 5 µs/div
500 mA Load Transient Response for Continuous
250 mA Load Transient Response for Discontinuous
=
=
=
=
Mode Operation. L 330 µH, COUT 300 µF
Mode Operation. L 68 µH, COUT 470 µF
DS011394-8
DS011394-9
Notes:
Notes:
A: Output Voltage, 50 mV/div.
AC Coupled
A: Output Voltage, 50 mV/div.
AC Coupled
B: 100 mA to 500 mA Load Pulse
Horizontal Time Base: 200 µs/div
B: 50 mA to 250 mA Load Pulse
Horizontal Time Base: 200 µs/div
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8
Block Diagram
DS011394-10
=
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.
FIGURE 1.
9
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Test Circuit and Layout Guidelines
Fixed Output Voltage Versions
DS011394-11
C
C
—
22 µF, 75V
Aluminum Electrolytic
220 µF, 25V
IN
—
OUT
Aluminum Electrolytic
D1
L1
—
—
Schottky, 11DQ06
330 µH, 52627
(for 5V in, 3.3V out, use
100 µH, RL-1284-100)
2k, 0.1%
R1
R2
—
—
6.12k, 0.1%
Adjustable Output Voltage Version
DS011394-12
FIGURE 2.
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 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 resis-
tors near the regulator, to keep the sensitive feedback wiring
short.
www.national.com
10
Test Circuit and Layout Guidelines
U.S. Source
(Continued)
Note 1: Pulse Engineering,
P.O. Box 12236, San Diego, CA 92112
(619) 674-8100
(516) 586-5566
Inductor
Value
Pulse Eng.
(Note 1)
*
Renco
NPI
(Note 3)
NP5915
NP5916
NP5917
NP5918/5919
NP5920/5921
NP5922
NP5923
*
(Note 2)
Note 2: Renco Electronics Inc.,
68 µH
RL-1284-68-43
RL-1284-100-43
RL-1284-150-43
RL-1284-220-43
RL-1284-330-43
RL-1284-470-43
RL-1283-680-43
RL-1283-1000-43
RL-1283-1500-43
RL-1283-2200-43
60 Jeffryn Blvd. East, Deer Park, NY 11729
*
100 µH
150 µH
220 µH
330 µH
470 µH
680 µH
1000 µH
1500 µH
2200 µH
*
Contact Manufacturer
52625
52626
52627
52628
52629
52631
*
European Source
Note 3: NPI/APC
+44 (0) 634 290588
47 Riverside, Medway City Estate
Strood, Rochester, Kent ME2 4DP.
UK
*
*
Contact Manufacturer
*
*
FIGURE 3. Inductor Selection by
Manufacturer’s Part Number
11
www.national.com
LM2574 Series Buck Regulator Design Procedure
PROCEDURE (Fixed Output Voltage Versions)
EXAMPLE (Fixed Output Voltage Versions)
Given:
Given:
=
=
VOUT 5V
VOUT Regulated Output Voltage (3.3V, 5V, 12V, or 15V)
=
=
VIN(Max) 15V
VIN(Max) Maximum Input Voltage
=
=
ILOAD(Max) Maximum Load Current
ILOAD(Max) 0.4A
1. Inductor Selection (L1)
1. Inductor Selection (L1)
A. Select the correct Inductor value selection guide from Fig-
ures 4, 5, 6, or Figure 7. (Output voltages of 3.3V, 5V, 12V or
15V respectively). For other output voltages, see the design
procedure for the adjustable version.
A. Use the selection guide shown in Figure 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 Figure
3, choose Pulse Engineering PE-52627, Renco RL-1284-330,
or NPI NP5920/5921.
B. From the inductor value selection guide, identify the induc-
tance region intersected by VIN(Max) and ILOAD(Max).
C. Select an appropriate inductor from the table shown in Fig-
ure 3. Part numbers are listed for three inductor manufactur-
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 ILOAD. For additional inductor information, see the in-
ductor section in the Application Hints section of this data
sheet.
2. Output Capacitor Selection (COUT
)
2. Output Capacitor Selection (COUT)
=
A. COUT 100 µF to 470 µF standard aluminum electrolytic.
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. Capacitor voltage rating 20V.
B. The capacitor’s voltage rating should be at least 1.5 times
greater than the output voltage. For a 5V regulator, a rating of
at least 8V is appropriate, and a 10V or 15V rating is recom-
mended.
Higher voltage electrolytic capacitors generally have lower
ESR numbers, and for this reason it may be necessary to se-
lect a capacitor rated for a higher voltage than would normally
be needed.
3. Catch Diode Selection (D1)
3. Catch Diode Selection (D1)
A. The catch-diode current rating must be at least 1.5 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 cur-
rent limit of the LM2574. The most stressful condition for this
diode is an overload or shorted output condition.
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 Figure 9.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
4. Input Capacitor (CIN
)
4. Input Capacitor (CIN)
An aluminum or tantalum electrolytic bypass capacitor located
close to the regulator is needed for stable operation.
A 22 µF aluminum electrolytic capacitor located near the input
and ground pins provides sufficient bypassing.
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12
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
DS011394-14
FIGURE 6. LM2574HV-12 Inductor Selection Guide
DS011394-13
DS011394-15
FIGURE 5. LM2574HV-5.0 Inductor Selection Guide
FIGURE 7. LM2574HV-15 Inductor Selection Guide
13
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LM2574 Series Buck Regulator Design Procedure (Continued)
DS011394-16
FIGURE 8. LM2574HV-ADJ Inductor Selection Guide
PROCEDURE (Adjustable Output Voltage Versions)
Given:
EXAMPLE (Adjustable Output Voltage Versions)
Given:
=
=
VOUT 24V
VOUT Regulated Output Voltage
=
=
VIN(Max) 40V
VIN(Max) Maximum Input Voltage
=
=
ILOAD(Max) 0.4A
ILOAD(Max) Maximum Load Current
=
=
F
Switching Frequency (Fixed at 52 kHz)
F
52 kHz
1. Programming Output Voltage (Selecting R1 and R2, as
1. Programming Output Voltage (Selecting R1 and R2)
shown in Figure 2)
Use the following formula to select the appropriate resistor
values.
=
=
R2 1k (19.51−1) 18.51k, closest 1% value is 18.7k
R1 can be between 1k and 5k. (For best temperature coeffi-
cient and stability with time, use 1% metal film resistors)
2. Inductor Selection (L1)
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant,
E • T (V • µs), from the following formula:
A. Calculate E • T (V • µs)
=
B. E • T 185 V • µs
=
C. ILOAD(Max) 0.4A
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 8.
=
D. Inductance Region 1000
=
E. Inductor Value 1000 µH Choose from Pulse Engineer-
C. On the horizontal axis, select the maximum load current.
ing Part #PE-52631, or Renco Part #RL-1283-1000.
D. Identify the inductance region intersected by the E • T
value and the maximum load current value, and note the in-
ductor value for that region.
E. Select an appropriate inductor from the table shown in Fig-
ure 3. Part numbers are listed for three inductor manufactur-
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 ILOAD. For additional inductor information, see the in-
ductor section in the application hints section of this data
sheet.
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14
LM2574 Series Buck Regulator Design Procedure (Continued)
PROCEDURE (Adjustable Output Voltage Versions)
3. Output Capacitor Selection (COUT
EXAMPLE (Adjustable Output Voltage Versions)
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:
However, for acceptable output ripple voltage select
COUT ≥ 100 µF
=
COUT 100 µF electrolytic capacitor
The above formula yields capacitor values between 5 µF and
1000 µF that will satisfy the loop requirements for stable op-
eration. 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 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 se-
lect a capacitor rate for a higher voltage than would normally
be needed.
4. Catch Diode Selection (D1)
4. Catch Diode Selection (D1)
A. The catch-diode current rating must be at least 1.5 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 cur-
rent limit of the LM2574. The most stressful condition for this
diode is an overload or shorted output condition. Suitable di-
odes are shown in the selection guide of Figure 9.
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.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
5. Input Capacitor (CIN
)
5. Input Capacitor (CIN)
An aluminum or tantalum electrolytic bypass capacitor located
close to the regulator is needed for stable operation.
A 22 µF aluminum electrolytic capacitor located near the input
and ground pins provides sufficient bypassing. See (Figure 9).
To further simplify the buck regulator design procedure, Na-
tional 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⁄
tional Semiconductor sales office in your area.
2
") diskette for IBM compatible computers from a Na-
15
www.national.com
LM2574 Series Buck Regulator Design Procedure (Continued)
VR
1 Amp Diodes
Schottky
1N5817
SR102
Fast Recovery
20V
MBR120P
1N5818
SR103
30V
40V
11DQ03
MBR130P
10JQ030
1N5819
SR104
The
following
diodes
are all
rated to
100V
11DQ04
11JQ04
MBR140P
MBR150
SR105
50V
60V
90V
11DF1
10JF1
11DQ05
11JQ05
MBR160
SR106
MUR110
HER102
11DQ06
11JQ06
11DQ09
FIGURE 9. Diode Selection Guide
INDUCTOR SELECTION
Application Hints
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.
INPUT CAPACITOR (CIN
)
To maintain stability, the regulator input pin must be by-
passed with at least a 22 µF electrolytic capacitor. The ca-
pacitor’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 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 LM2574 (or any of the Simple Switcher family) can be
used for both continuous and discontinuous modes of opera-
tion.
In many cases the preferred mode of operation is in the con-
tinuous mode. It offers better load regulation, lower peak
switch, inductor and diode currents, and can have lower out-
put ripple voltage. But it does require relatively large inductor
values to keep the inductor current flowing continuously, es-
pecially at low output load currents.
To simplify the inductor selection process, an inductor selec-
tion guide (nomograph) was designed (see Figure 4 through
Figure 8). This guide assumes continuous mode operation,
and selects an inductor that will allow a peak-to-peak induc-
tor ripple current (∆IIND) to be a certain percentage of the
maximum design load current. In the LM2574 SIMPLE
SWITCHER, the peak-to-peak inductor ripple current per-
centage (of load current) is allowed to change as different
design load currents are selected. By allowing the percent-
age of inductor ripple current to increase for lower current
applications, the inductor size and value can be kept rela-
tively low.
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16
the output ripple voltage can be calculated, or conversely,
Application Hints (Continued)
measuring the output ripple voltage and knowing the ∆IIND
,
INDUCTOR RIPPLE CURRENT
the ESR can be calculated.
When the switcher is operating in the continuous mode, the
inductor current waveform ranges from a triangular to a saw-
tooth type of waveform (depending on the input voltage). For
a given input voltage and output voltage, the peak-to-peak
amplitude of this inductor current waveform remains con-
stant. As the load current rises or falls, the entire sawtooth
current waveform also rises or falls. The average DC value
of this waveform is equal to the DC load current (in the buck
regulator configuration).
From the previous example, the Peak-to-peak Inductor
=
Ripple Current (∆IIND
)
212 mA p-p. Once the ∆IND value is
known, the following three formulas can be used to calculate
additional information about the switching regulator circuit:
1. Peak Inductor or peak switch current
2. Minimum load current before the circuit becomes dis-
continuous
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.
=
3. Output Ripple Voltage (∆IIND) x (ESR of COUT
)
The selection guide chooses inductor values suitable for
continuous mode operation, but if the inductor value chosen
is prohibitively high, the designer should investigate the pos-
sibility of discontinuous operation. The computer design soft-
ware Switchers Made Simple will provide all component
values for discontinuous (as well as continuous) mode of op-
eration.
The curve shown in Figure 10 illustrates how the peak-to-
peak inductor ripple current (∆IIND) is allowed to change as
different maximum load currents are selected, and also how
it changes as the operating point varies from the upper bor-
der to the lower border within an inductance region (see In-
ductor Selection guides).
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 ex-
pensive, the bobbin core type, consists of wire wrapped on a
ferrite rod core. This type of construction makes for an inex-
pensive inductor, but since the magnetic flux is not com-
pletely contained within the core, it generates more electro-
magnetic interference (EMI). This EMl can cause problems
in sensitive circuits, or can give incorrect scope readings be-
cause 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 be-
gins 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 in-
ductor types have different saturation characteristics, and
this should be kept in mind when selecting an inductor. The
inductor manufacturers’ data sheets include current and en-
ergy limits to avoid inductor saturation.
DS011394-18
FIGURE 10. Inductor Ripple Current (∆IIND) Range
Based on Selection Guides from Figure 4 through
Figure 8.
Consider the following example:
=
@
VOUT 5V 0.4A
=
VIN 10V minimum up to 20V maximum
The selection guide in Figure 5 shows that for a 0.4A load
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 (∆IIND) to flow that will be a percentage of the maxi-
mum load current. For this inductor value, the ∆IIND will also
vary depending on the input voltage. As the input voltage in-
creases to 20V, it approaches the upper border of the induc-
tance region, and the inductor ripple current increases. Re-
ferring to the curve in Figure 10, it can be seen that at the
0.4A load current level, and operating near the upper border
of the 330 µH inductance region, the ∆IIND will be 53% of
0.4A, or 212 mA p-p.
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 LM2574 using short pc board traces. Standard alu-
minum electrolytics are usually adequate, but low ESR types
are recommended for low output ripple voltage and good
stability. The ESR of a capacitor depends on many factors,
some which are: the value, the voltage rating, physical size
and the type of construction. In general, low value or low
voltage (less than 12V) electrolytic capacitors usually have
higher ESR numbers.
This ∆IIND is important because from this number the peak
inductor current rating can be determined, the minimum load
current required before the circuit goes to discontinuous op-
eration, and also, knowing the ESR of the output capacitor,
The amount of output ripple voltage is primarily a function of
the ESR (Equivalent Series Resistance) of the output ca-
17
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FEEDBACK CONNECTION
Application Hints (Continued)
The LM2574 (fixed voltage versions) feedback pin must be
wired to the output voltage point of the switching power sup-
ply. When using the adjustable version, physically locate
both output voltage programming resistors near the LM2574
to avoid picking up unwanted noise. Avoid using resistors
greater than 100 kΩ because of the increased chance of
noise pickup.
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 (100 µF- 330 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.
ON /OFF INPUT
=
Output Ripple Voltage (∆IIND) (ESR of COUT
)
For normal operation, the ON /OFF pin should be grounded
or driven with a low-level TTL voltage (typically below 1.6V).
To put the regulator into standby mode, drive this pin with a
high-level TTL or CMOS signal. The ON /OFF pin can be
safely pulled up to +VIN without a resistor in series with it.
The ON /OFF pin should not be left open.
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.
GROUNDING
Tantalum capacitors can have a very low ESR, and should
be carefully evaluated if it is the only output capacitor. Be-
cause of their good low temperature characteristics, a tanta-
lum can be used in parallel with aluminum electrolytics, with
the tantalum making up 10% or 20% of the total capacitance.
The 8-pin molded DIP and the 14-pin surface mount pack-
age have separate power and signal ground pins. Both
ground pins should be soldered directly to wide printed cir-
cuit board copper traces to assure low inductance connec-
tions and good thermal properties.
The capacitor’s ripple current rating at 52 kHz should be at
least 50% higher than the peak-to-peak inductor ripple cur-
rent.
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 recom-
mended because of the additional thermal resistance it intro-
duces, and the resultant higher junction temperature.
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 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 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 Figure 9 for Schot-
tky and “soft” fast-recovery diode selection guide.
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.
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.
A curve displaying thermal resistance vs. pc board area for
the two packages is shown in the Typical Performance Char-
acteristics curves section of this data sheet.
The output ripple voltage is due mainly to the inductor saw-
tooth ripple current multiplied by the ESR of the output ca-
pacitor. (See the inductor selection in the application hints.)
These thermal resistance numbers are approximate, and
there can be many factors that will affect the final thermal re-
sistance. Some of these factors include board size, shape,
thickness, position, location, and board temperature. Other
factors are, the area of printed circuit copper, copper thick-
ness, 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. Further-
more, 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 coeffi-
cient at higher temperatures.
The voltage spikes are present because of the the fast
switching action of the output switch, and the parasitic induc-
tance of the output filter capacitor. To minimize these voltage
spikes, special low inductance capacitors can be used, and
their lead lengths must be kept short. Wiring inductance,
stray capacitance, as well as the scope probe used to evalu-
ate these transients, all contribute to the amplitude of these
spikes.
An additional small LC filter (20 µH & 100 µF) can be added
to the output (as shown in Figure 16 ) 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.
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18
The power dissipation (PD) for the IC could be measured, or
it can be estimated by using the formula:
Application Hints (Continued)
The data sheet thermal resistance curves and the thermal
model in Switchers Made Simple software (version 3.3)
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 fol-
lowing equation.
Where IS is obtained from the typical supply current curve
(adjustable version use the supply current vs. duty cycle
curve).
=
Tj Tcu + (θj-cu x PD)
With the switcher operating under worst case conditions and
all other components on the board in the intended enclosure,
measure the copper temperature (Tcu ) near the IC. This can
be done by temporarily soldering a small thermocouple to
the pc board copper near the IC, or by holding a small ther-
mocouple on the pc board copper using thermal grease for
good thermal conduction.
Additional Applications
INVERTING REGULATOR
Figure 11 shows a LM2574-12 in a buck-boost configuration
to generate a negative 12V output from a positive input volt-
age. This circuit bootstraps the regulator’s ground pin to the
negative output voltage, then by grounding the feedback pin,
the regulator senses the inverted output voltage and regu-
lates it to −12V.
The thermal resistance (θj-cu) for the two packages is:
=
θj-cu 42˚C/W for the N-8 package
=
θj-cu 52˚C/W for the M-14 package
DS011394-19
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.
Where fosc 52 kHz. Under normal continuous inductor cur-
rent operating conditions, the minimum VIN represents the
worst case. Select an inductor that is rated for the peak cur-
rent anticipated.
The switch currents in this buck-boost configuration are
higher than in the standard buck-mode design, thus lowering
the available output current. Also, the start-up input current
of the buck-boost converter is higher than the standard buck-
mode regulator, and this may overload an input power
source with a current limit less than 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.
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
Because of the structural differences between the buck and
the buck-boost regulator topologies, the buck regulator de-
sign procedure section can not be used to to select the in-
ductor or the output capacitor. The recommended range of
inductor values for the buck-boost design is between 68 µH
and 220 µH, and the output capacitor values must be larger
than what is normally required for buck designs. Low input
voltages or high output currents require a large value output
capacitor (in the thousands of micro Farads).
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.
The peak inductor current, which is the same as the peak
switch current, can be calculated from the following formula:
19
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Additional Applications (Continued)
DS011394-21
Note: Complete circuit not shown.
DS011394-20
Note: Pin numbers are for 8-pin DIP package.
Note: Pin numbers are for 8-pin DIP package.
FIGURE 13. Undervoltage Lockout for Buck Circuit
FIGURE 12. Negative Boost
Because of the boosting function of this type of regulator, the
switch current is relatively high, especially at low input volt-
ages. Output load current limitations are a result of the maxi-
mum current rating of the switch. Also, boost regulators can
not provide current limiting load protection in the event of a
shorted load, so some other means (such as a fuse) may be
necessary.
UNDERVOLTAGE LOCKOUT
In some applications it is desirable to keep the regulator off
until the input voltage reaches a certain threshold. An under-
voltage lockout circuit which accomplishes this task is shown
in Figure 13 while Figure 14 shows the same circuit applied
to a buck-boost configuration. These circuits keep the regu-
lator off until the input voltage reaches a predetermined
level.
DS011394-22
Note: Complete circuit not shown (see Figure 11 ).
Note: Pin numbers are for 8-pin DIP package.
FIGURE 14. Undervoltage Lockout
for Buck-Boost Circuit
VTH ≈ VZ1 + 2VBE (Q1)
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 approxi-
mately 10 ms of delay time before the circuit begins switch-
ing. Increasing the RC time constant can provide longer de-
lay times. But excessively large RC time constants can
cause problems with input voltages that are high in 60 Hz or
120 Hz ripple, by coupling the ripple into the ON /OFF pin.
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 re-
duces the output ripple by a factor of 10 or more is included
in this circuit.
DS011394-23
Note: Complete circuit not shown.
Note: Pin numbers are for 8-pin DIP package.
FIGURE 15. Delayed Startup
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20
Additional Applications (Continued)
DS011394-24
Note: Pin numbers are for 8-pin DIP package.
FIGURE 16. 1.2V to 55V Adjustable 500 mA Power Supply with Low Output Ripple
grade capacitors (“low-ESR”, “high-frequency”, or “low-
inductance”) in the 100 µF–1000 µF range generally have
ESR of less than 0.15Ω.
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.
EQUIVALENT SERIES INDUCTANCE (ESL)
The pure inductance component of a capacitor (see Figure
17). The amount of inductance is determined to a large ex-
tent on the capacitor’s construction. In a buck regulator, this
unwanted inductance causes voltage spikes to appear on
the output.
BUCK-BOOST REGULATOR
A switching regulator topology in which a positive voltage is
converted to a negative voltage without a transformer.
OUTPUT RIPPLE VOLTAGE
DUTY CYCLE (D)
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.
Ratio of the output switch’s on-time to the oscillator period.
CAPACITOR RIPPLE CURRENT
RMS value of the maximum allowable alternating current at
which a capacitor can be operated continuously at a speci-
fied temperature.
CATCH DIODE OR CURRENT STEERING DIODE
The diode which provides a return path for the load current
when the LM2574 switch is OFF.
STANDBY QUIESCENT CURRENT (ISTBY
)
EFFICIENCY (η)
Supply current required by the LM2574 when in the standby
mode (ON/OFF pin is driven to TTL-high voltage, thus turn-
ing the output switch OFF).
The proportion of input power actually delivered to the load.
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).
CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)
The purely resistive component of a real capacitor’s imped-
ance (see Figure 17). It causes power loss resulting in ca-
pacitor heating, which directly affects the capacitor’s operat-
ing lifetime. When used as a switching regulator output filter,
higher ESR values result in higher output ripple voltages.
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.
DS011394-25
FIGURE 17. 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-
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OPERATING VOLT MICROSECOND CONSTANT (E•Top
)
Definition of Terms (Continued)
The product (in VoIt•µs) of the voltage applied to the inductor
and the time the voltage is applied. This E•Top constant is a
measure of the energy handling capability of an inductor and
is dependent upon the type of core, the core area, the num-
ber of turns, and the duty cycle.
INDUCTOR SATURATION
The condition which exists when an inductor cannot hold any
more magnetic flux. When an inductor saturates, the induc-
tor appears less inductive and the resistive component domi-
nates. Inductor current is then limited only by the DC resis-
tance of the wire and the available source current.
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22
Physical Dimensions inches (millimeters) unless otherwise noted
14-Lead Wide Surface Mount (WM)
Order Number LM2574M-3.3, LM2574HVM-3.3, LM2574M-5.0,
LM2574HVM-5.0, LM2574M-12, LM2574HVM-12, LM2574M-15,
LM2574HVM-15, LM2574M-ADJ or LM2574HVM-ADJ
NS Package Number M14B
23
www.national.com
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
8-Lead DIP (N)
Order Number LM2574M-3.3, LM2574HVM-3.3, LM2574HVN-5.0, LM2574HVN-12,
LM2574HVN-15, LM2574HVN-ADJ, LM2574N-5.0,
LM2574N-12, LM2574N-15 or LM2574N-ADJ
NS Package Number N08A
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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
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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
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2. A critical component is any component of a life
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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.
See Wireless Products
Products > Analog - Regulators > Simple Switchers > LM2574
LM2574 Product Folder
SIMPLE SWITCHER 0.5A Step-Down Voltage Regulator
LM2594 - lower cost, higher efficiency, smaller solution size
LM2597 - lower cost, higher efficiency, smaller solution size
LM2674 - very high efficiency, much smaller solution size
LM2671 - LOWER COST, HIGHER EFFICIENCY, SMALLER SOLUTION SIZE.
See Also:
Generic P/N 2574
General
Package
& Models
Samples
& Pricing
Design
Tools
Application
Notes
Features
Datasheet
Description
WEBENCH Live Simulation!
Parametric Table
Multiple Output Capability
On/Off Pin
No
Yes
No
4
LM2574 Webench™ Custom
Design/Analyze/Build It
Error Flag
V in Lower
11.0
V in Upper
Input Voltage, min (Volt)
Input Voltage, max (Volt)
Output Current, max
Output Voltage (Volt)
Adjustable Output Voltage
Switching Frequency (Hz)
Adjustable Switching Frequency
Sync Pin
4.8 <=
V out
I out
<=
13.0
<= 40.0
<= 37.0
<= 0.50
<= 100
V
V
40, 60
500 mA
12, 15, 3.30, 5
No, Yes
52000
No
1.2 <=
3.3
V
0.40
A
Ambient Temperature
30
°C
No
Create This Design
Efficiency (%)
88, 72, 77
No
What is Webench?
Flyback
Inverting
Yes
Step-down
Yes
-
Datasheet
Size in
Kbytes
Title
Date
Receive via
Email
Download
View Online
30-
Jun-
99
Receive via
Email
LM2574 LM2574HV SIMPLE SWITCHER 0.5A Step-Down 639
View Online Download
Voltage Regulator
Kbytes
LM2574 LM2574HV SIMPLE SWITCHER 0.5A Step-Down
Voltage Regulator (JAPANESE)
840
Kbytes
View Online Download
Receive via
If you have trouble printing or viewing PDF file(s), see Printing Problems.
Package Availability, Models, Samples & Pricing
Budgetary
Pricing
Samples &
Electronic
Orders
Std
Pack
Size
Package
Models
Package
Marking
Part Number
Status
Type Pins MSL
SPICE IBIS
Qty $US each
24 Hour
rail
of
50
[logo]¢U¢Z¢2¢T
LM2574M
SOIC
WIDE
Full
production
MSL
MSL
MSL
LM2574M-12
LM2574M-15
LM2574M-3.3
14
14
14
N/A
N/A
N/A
N/A
N/A
N/A
1K+ $0.7200
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-12 P+
rail
of
50
[logo]¢U¢Z¢2¢T
LM2574M
SOIC
WIDE
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1K+ $0.7200
1K+ $0.7200
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rail
of
50
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LM2574M
SOIC
WIDE
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production
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-3.3 P+
24 Hour
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of
50
[logo]¢U¢Z¢2¢T
LM2574M
SOIC
WIDE
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production
MSL
MSL
LM2574M-5.0
LM2574M-ADJ
14
14
N/A
N/A
N/A
N/A
1K+ $0.7200
1K+ $0.7200
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-5.0 P+
Samples
rail
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SOIC
WIDE
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-ADJ P+
reel [logo]¢U¢Z¢2¢T
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WIDE
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production
MSL
MSL
MSL
MSL
MSL
LM2574MX-12
LM2574MX-15
LM2574MX-3.3
LM2574MX-5.0
LM2574MX-ADJ
14
14
14
14
14
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
1K+ $0.7200
1K+ $0.7200
1K+ $0.7200
1K+ $0.7200
1K+ $0.7200
of
1000
LM2574M
-12 P+
Buy Now
reel [logo]¢U¢Z¢2¢T
SOIC
WIDE
Full
production
of
1000
LM2574M
-15 P+
reel [logo]¢U¢Z¢2¢T
SOIC
WIDE
Full
production
of
1000
LM2574M
-3.3 P+
reel [logo]¢U¢Z¢2¢T
SOIC
WIDE
Full
production
of
1000
LM2574M
-5.0 P+
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reel [logo]¢U¢Z¢2¢T
SOIC
WIDE
Full
production
of
1000
LM2574M
-ADJ P+
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24 Hour
rail
of
40
[logo]¢U¢Z¢2¢T
LM2574N
Full
production
MDIP
MDIP
MDIP
MSL
MSL
MSL
LM2574N-12
LM2574N-15
LM2574N-3.3
8
8
8
N/A
N/A
N/A
N/A
N/A
N/A
1K+ $0.7200
1K+ $0.7200
1K+ $0.7200
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-12 P+
24 Hour
rail
of
40
[logo]¢U¢Z¢2¢T
LM2574N
Full
production
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-15 P+
Samples
rail
of
40
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LM2574N
Full
production
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-3.3 P+
24 Hour
rail
of
40
[logo]¢U¢Z¢2¢T
LM2574N
Full
production
MDIP
MDIP
MSL
MSL
LM2574N-5.0
LM2574N-ADJ
8
8
N/A
N/A
N/A
N/A
1K+ $0.7200
1K+ $0.7200
Buy Now
-5.0 P+
24 Hour
rail
of
40
[logo]¢U¢Z¢2¢T
LM2574N
Full
production
Buy Now
-ADJ P+
tray
of
N/A
Full
production
Samples
Samples
Samples
Samples
Samples
Samples
Samples
Samples
Samples
Die
LM2574-12 MDC
LM2574-15 MDC
LM2574-3.3 MDC
LM2574-5.0 MDC
LM2574-ADJ MDC
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
-
-
-
-
-
-
-
-
-
tray
of
N/A
Full
production
Die
Die
Die
Die
Die
Die
Die
Die
tray
of
N/A
Full
production
tray
of
N/A
Full
production
tray
of
N/A
Full
production
tray
of
N/A
LM2574HV-12
MDC
Full
production
tray
of
N/A
LM2574HV-15
MDC
Full
production
tray
of
N/A
LM2574HV3.3
MDC
Full
production
tray
of
N/A
LM2574HVADJ
MDC
Full
production
wafer
jar
of
Full
production
Wafer
Wafer
Wafer
Wafer
Wafer
LM2574-12 MWC
LM2574-15 MWC
LM2574-3.3 MWC
LM2574-5.0 MWC
LM2574-ADJ MWC
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
-
-
-
-
-
N/A
wafer
jar
of
Full
production
N/A
wafer
jar
of
Full
production
N/A
wafer
jar
of
Full
production
N/A
wafer
jar
of
Full
production
N/A
wafer
jar
of
LM2574HV-12
MWC
Full
production
Wafer
Wafer
Wafer
Wafer
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
-
-
-
-
N/A
wafer
jar
of
LM2574HV-15
MWC
Full
production
N/A
wafer
jar
of
LM2574HV3.3
MWC
Full
production
N/A
wafer
jar
of
LM2574HVADJ
MWC
Full
production
N/A
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 a minimum number 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 ±4% tolerance on output voltage within specified input voltages and
output load conditions, and ±10% on the oscillator frequency. External shutdown is included, featuring 50 µA
(typical) standby current. The output switch includes cycle-by-cycle current limiting, as well as thermal
shutdown for full protection under fault conditions.
Features
●
●
3.3V, 5V, 12V, 15V, and adjustable output versions
Adjustable version output voltage range, 1.23V to 37V (57V for HV version) ±4% max over line and
load conditions
●
●
●
●
●
●
●
●
Guaranteed 0.5A output current
Wide input voltage range, 40V, up to 60V for HV version
Requires only 4 external components
52 kHz fixed frequency internal oscillator
TTL shutdown capability, low power standby mode
High efficiency
Uses readily available standard inductors
Thermal shutdown and current limit protection
Applications
●
●
●
●
Simple high-efficiency step-down (buck) regulator
Efficient pre-regulator for linear regulators
On-card switching regulators
Positive to negative converter (Buck-Boost)
Design Tools
Title
Size in Kbytes Date
Receive via
Email
Download
View Online
SimpleSwitcher® DC-DC
Converters Design Software
12-Jun-
2002
View
10 Kbytes
If you have trouble printing or viewing PDF file(s), see Printing Problems.
Application Notes
Title
Size in Kbytes Date
Receive via Email
Download
View Online
AN-1061: AN-1061 Power
Conversion in Line-Powered
Equipment
View Online Download Receive via Email
View Online Download Receive via Email
142 Kbytes
229 Kbytes
5-Jan-97
AN-1229: Application Note 1229
SIMPLE SWITCHER PCB Layout
Guidelines
29-Jul-02
If you have trouble printing or viewing PDF file(s), see Printing Problems.
[Information as of 5-Aug-2002]
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Feedback
See A/D Converters
Products
Products > Analog - Regulators > Simple Switchers > LM2574HV
LM2574HV Product Folder
SIMPLE SWITCHER 0.5A Step-Down Voltage Regulator
Generic P/N 2574HV
General
Description
Package
& Models
Samples
& Pricing
Application
Notes
Features
Datasheet
WEBENCH Live Simulation!
Parametric Table
Multiple Output Capability
On/Off Pin
No
LM2574HV Webench™ Custom
Design/Analyze/Build It
Yes
Error Flag
No
V in Lower
V in Upper
Input Voltage, min (Volt)
Input Voltage, max (Volt)
Output Current, max
Output Voltage (Volt)
Adjustable Output Voltage
Switching Frequency (Hz)
4
4.8 <=
V out
I out
<=
<= 60.0
<= 57.0
<= 0.50
<= 100
11.0
13.0
V
V
60
1.2 <=
3.3
500 mA
12, 15, 3.30, 5
No, Yes
52000
No
V
0.40
A
Ambient Temperature
30
°C
Adjustable Switching Frequency
Sync Pin
No
Create This Design
Efficiency (%)
Flyback
88, 72, 77
No
What is Webench?
Inverting
Yes
Step-down
Yes
-
Datasheet
Size in
Kbytes
Title
Date
Receive via
Email
Download
View Online
30-
Jun-
99
Receive via
Email
LM2574 LM2574HV SIMPLE SWITCHER 0.5A Step-Down 639
View Online Download
Voltage Regulator
Kbytes
LM2574 LM2574HV SIMPLE SWITCHER 0.5A Step-Down
Voltage Regulator (JAPANESE)
605
Kbytes
View Online Download
Receive via
If you have trouble printing or viewing PDF file(s), see Printing Problems.
Package Availability, Models, Samples & Pricing
Budgetary
Pricing
Samples &
Electronic
Orders
Std
Pack
Size
Package
Models
Package
Marking
Part Number
Status
Type Pins MSL
SPICE IBIS
Qty $US each
24 Hour
rail
of
50
[logo]¢U¢Z¢2¢T
LM2574HVM
-12 P+
SOIC
WIDE
Full
production
MSL
MSL
MSL
MSL
MSL
LM2574HVM-12
14
14
14
14
14
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
1K+ $2.0500
Buy Now
Samples
rail
of
50
[logo]¢U¢Z¢2¢T
LM2574HVM
-15 P+
SOIC
WIDE
Full
production
LM2574HVM-15
LM2574HVM-3.3
LM2574HVM-5.0
LM2574HVM-ADJ
1K+ $2.0500
1K+ $2.0500
1K+ $2.0500
1K+ $2.0500
Buy Now
24 Hour
rail
of
50
[logo]¢U¢Z¢2¢T
LM2574HVM
-3.3 P+
SOIC
WIDE
Full
production
Buy Now
24 Hour
rail
of
50
[logo]¢U¢Z¢2¢T
LM2574HVM
-5.0 P+
SOIC
WIDE
Full
production
Buy Now
24 Hour
rail
of
50
[logo]¢U¢Z¢2¢T
LM2574HVM
-ADJ P+
SOIC
WIDE
Full
production
Buy Now
reel [logo]¢U¢Z¢2¢T
SOIC
WIDE
Full
production
MSL
MSL
MSL
MSL
MSL
LM2574HVMX-12
LM2574HVMX-15
LM2574HVMX-3.3
LM2574HVMX-5.0
LM2574HVMX-ADJ
14
14
14
14
14
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
1K+ $2.0500
1K+ $2.0500
1K+ $2.0500
1K+ $2.0500
1K+ $2.0500
of
1000
LM2574HVM
-12 P+
Buy Now
reel [logo]¢U¢Z¢2¢T
SOIC
WIDE
Full
production
of
1000
LM2574HVM
-15 P+
reel [logo]¢U¢Z¢2¢T
SOIC
WIDE
Full
production
of
1000
LM2574HVM
-3.3 P+
reel [logo]¢U¢Z¢2¢T
SOIC
WIDE
Full
production
of
1000
LM2574HVM
-5.0 P+
Buy Now
reel [logo]¢U¢Z¢2¢T
SOIC
WIDE
Full
production
of
1000
LM2574HVM
-ADJ P+
Buy Now
24 Hour
rail
of
40
[logo]¢U¢Z¢2¢T
LM2574HVN
-12 P+
Full
production
MDIP
MDIP
MDIP
MDIP
MSL
MSL
MSL
MSL
LM2574HVN-12
LM2574HVN-15
LM2574HVN-3.3
LM2574HVN-5.0
8
8
8
8
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
1K+ $2.0500
1K+ $2.0500
1K+ $2.0500
1K+ $2.0500
Buy Now
Samples
rail
of
40
[logo]¢U¢Z¢2¢T
LM2574HVN
-15 P+
Full
production
Buy Now
24 Hour
rail
of
40
[logo]¢U¢Z¢2¢T
LM2574HVN
-3.3 P+
Full
production
Buy Now
24 Hour
rail
of
40
[logo]¢U¢Z¢2¢T
LM2574HVN
-5.0 P+
Full
production
Buy Now
24 Hour
rail
of
40
[logo]¢U¢Z¢2¢T
LM2574HVN
-ADJ P+
Full
production
MDIP
MSL
LM2574HVN-ADJ
LM2574HV-5 MDC
8
N/A
N/A
N/A
N/A
N/A
N/A
1K+ $2.0500
Buy Now
tray
of
N/A
Full
production
Die
-
-
wafer
jar
of
LM2574HV-5
MWC
Full
production
Wafer
N/A
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 a minimum number 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 ±4% tolerance on output voltage within specified input voltages and
output load conditions, and ±10% on the oscillator frequency. External shutdown is included, featuring 50 µA
(typical) standby current. The output switch includes cycle-by-cycle current limiting, as well as thermal
shutdown for full protection under fault conditions.
Features
●
●
3.3V, 5V, 12V, 15V, and adjustable output versions
Adjustable version output voltage range, 1.23V to 37V (57V for HV version) ±4% max over line and
load conditions
●
●
●
●
●
●
●
●
Guaranteed 0.5A output current
Wide input voltage range, 40V, up to 60V for HV version
Requires only 4 external components
52 kHz fixed frequency internal oscillator
TTL shutdown capability, low power standby mode
High efficiency
Uses readily available standard inductors
Thermal shutdown and current limit protection
Applications
●
●
●
●
Simple high-efficiency step-down (buck) regulator
Efficient pre-regulator for linear regulators
On-card switching regulators
Positive to negative converter (Buck-Boost)
Application Notes
Title
Size in Kbytes Date
Receive via Email
Download
View Online
AN-1061: AN-1061 Power
Conversion in Line-Powered
Equipment
View Online Download Receive via Email
View Online Download Receive via Email
142 Kbytes
229 Kbytes
5-Jan-97
AN-1229: Application Note 1229
SIMPLE SWITCHER PCB Layout
Guidelines
29-Jul-02
If you have trouble printing or viewing PDF file(s), see Printing Problems.
[Information as of 5-Aug-2002]
Search
Design
Purchasing
Quality
Company
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Contact Us . Site Terms & Conditions of Use . Copyright 2002 © National Semiconductor Corporation . My Preferences .
Feedback
LM2574-15MWC 相关器件
型号 | 制造商 | 描述 | 价格 | 文档 |
LM2574-3.3 | MOTOROLA | EASY SWITCHERE⑩ 0.5 A STEP-DOWN VOLTAGE REGULATOR | 获取价格 | |
LM2574-3.3BN | MICREL | 52KHZ SIMPLE 0.5A BUCK REGULATOR | 获取价格 | |
LM2574-3.3BWM | MICREL | 52kHz Simple 0.5A Buck Regulator | 获取价格 | |
LM2574-3.3BWMT&R | MICREL | Switching Regulator, Voltage-mode, 1.8A, 63kHz Switching Freq-Max, PDSO14, 0.300 INCH, SOIC-14 | 获取价格 | |
LM2574-3.3BWMT&R | MICROCHIP | Switching Regulator, Voltage-mode, 1.8A, 63kHz Switching Freq-Max, PDSO14, 0.300 INCH, SOIC-14 | 获取价格 | |
LM2574-3.3HVN | NSC | SIMPLE SWITCHER⑩ 0.5A Step-Down Voltage Regulator | 获取价格 | |
LM2574-3.3MDC | NSC | IC 1.8 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, UUC, DIE, Switching Regulator or Controller | 获取价格 | |
LM2574-3.3MWC | NSC | IC 1.8 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, UUC, WAFER, Switching Regulator or Controller | 获取价格 | |
LM2574-3.3YN | MICREL | 52kHz Simple 0.5A Buck Regulator | 获取价格 | |
LM2574-5 | MOTOROLA | EASY SWITCHERE⑩ 0.5 A STEP-DOWN VOLTAGE REGULATOR | 获取价格 |
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