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  • 北京元坤伟业科技有限公司

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  • 深圳市英德州科技有限公司

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  • 数量38200 
  • 厂家TI(德州仪器) 
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  • 数量2015 
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  • 数量
  • 厂家22+ 
  • 封装36-SSOP(0.209,5.30mm 宽) 
  • 批号12560 
  • 十年资质★★稳定供货
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产品型号LM2574N-ADJ的概述

LM2574N-ADJ概述 LM2574N-ADJ是一款由国家半导体(National Semiconductor)公司设计和制造的降压型开关稳压器,其主要功能是将输入电压转换为稳定的输出电压。该芯片特别适用于需要较高电流输出的应用场合,其调节范围广泛,可通过外部电阻轻松调节输出电压,适用于3V至40V的输入电压范围。 LM2574N-ADJ的设计采用了一种集成开关结构,同时实现低待机电流、抗干扰、易于设计等优点,广受工程师和设计师的青睐。该芯片内部集成了电流限制和热保护功能,能够有效防止元件损坏,提高系统的可靠性。此外,其输出电流最大可达到1A,适合多种应用场景,从简单的电源供应到复杂的电源管理系统,均可找到其身影。 LM2574N-ADJ的详细参数 LM2574N-ADJ的主要技术参数如下: - 输入电压范围:3V 至 40V - 输出电压可调范围:1.23V 至 37V - 输出...

产品型号LM2574N-ADJ的Datasheet PDF文件预览

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 k)  
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)  
www.national.com  
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  
www.national.com  
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 0  
Note: Pin numbers are for the 8-pin DIP package.  
FIGURE 1.  
9
www.national.com  
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.  
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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  
www.national.com  
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.  
www.national.com  
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.  
www.national.com  
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 kbecause 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  
0.03can 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.  
www.national.com  
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  
www.national.com  
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 0.15.  
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 0.5to 0.1ESR. Higher-  
21  
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OPERATING VOLT MICROSECOND CONSTANT (ETop  
)
Definition of Terms (Continued)  
The product (in VoItµs) of the voltage applied to the inductor  
and the time the voltage is applied. This ETop 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.  
www.national.com  
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  
LIFE SUPPORT POLICY  
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT  
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL  
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:  
1. Life support devices or systems are devices or  
systems which, (a) are intended for surgical implant  
into the body, or (b) support or sustain life, and  
whose failure to perform when properly used in  
accordance with instructions for use provided in the  
labeling, can be reasonably expected to result in a  
significant injury to the user.  
2. A critical component is any component of a life  
support device or system whose failure to perform  
can be reasonably expected to cause the failure of  
the life support device or system, or to affect its  
safety or effectiveness.  
National Semiconductor  
Corporation  
Americas  
Tel: 1-800-272-9959  
Fax: 1-800-737-7018  
Email: support@nsc.com  
National Semiconductor  
Europe  
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Response Group  
Tel: 65-2544466  
Fax: 65-2504466  
National Semiconductor  
Japan Ltd.  
Tel: 81-3-5639-7560  
Fax: 81-3-5639-7507  
Fax: +49 (0) 1 80-530 85 86  
Email: europe.support@nsc.com  
Deutsch Tel: +49 (0) 1 80-530 85 85  
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Italiano Tel: +49 (0) 1 80-534 16 80  
Email: sea.support@nsc.com  
www.national.com  
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.  
配单直通车
LM2574N-ADJ产品参数
型号:LM2574N-ADJ
生命周期:Transferred
零件包装代码:DIP
包装说明:DIP,
针数:8
Reach Compliance Code:unknown
ECCN代码:EAR99
HTS代码:8542.39.00.01
风险等级:5.09
模拟集成电路 - 其他类型:SWITCHING REGULATOR
最大输入电压:40 V
最小输入电压:7 V
标称输入电压:12 V
JESD-30 代码:R-PDIP-T8
JESD-609代码:e0
长度:9.78 mm
功能数量:1
端子数量:8
最大输出电流:1.8 A
标称输出电压:1.23 V
封装主体材料:PLASTIC/EPOXY
封装代码:DIP
封装形状:RECTANGULAR
封装形式:IN-LINE
认证状态:Not Qualified
座面最大高度:4.45 mm
表面贴装:NO
切换器配置:BUCK
最大切换频率:63 kHz
端子面层:Tin/Lead (Sn/Pb)
端子形式:THROUGH-HOLE
端子节距:2.54 mm
端子位置:DUAL
宽度:7.62 mm
Base Number Matches:1
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