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LM2575T-12 参数 Datasheet PDF下载

LM2575T-12图片预览
型号: LM2575T-12
PDF下载: 下载PDF文件 查看货源
内容描述: SIMPLE SWITCHER 1A降压稳压器 [SIMPLE SWITCHER 1A Step-Down Voltage Regulator]
分类和应用: 稳压器
文件页数/大小: 27 页 / 718 K
品牌: NSC [ National Semiconductor ]
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LM2575 Series Buck Regulator Design Procedure  
PROCEDURE (Fixed Output Voltage Versions)  
Given: VOUT = Regulated Output Voltage (3.3V, 5V, 12V, or  
15V) VIN(Max) = Maximum Input Voltage ILOAD(Max) =  
Maximum Load Current  
EXAMPLE (Fixed Output Voltage Versions)  
Given: VOUT = 5V VIN(Max) = 20V ILOAD(Max) = 0.8A  
1. Inductor Selection (L1) A. Select the correct Inductor  
value selection guide from Figures 3, 4, 5, 6 (Output  
voltages of 3.3V, 5V, 12V or 15V respectively). For other  
output voltages, see the design procedure for the adjustable  
version. B. From the inductor value selection guide, identify  
the inductance region intersected by VIN(Max) and  
ILOAD(Max), and note the inductor code for that region. C.  
Identify the inductor value from the inductor code, and  
select an appropriate inductor from the table shown in  
Figure 9. Part numbers are listed for three inductor  
manufacturers. The inductor chosen must be rated for  
operation at the LM2575 switching frequency (52 kHz) and  
for a current rating of 1.15 x ILOAD. For additional inductor  
information, see the inductor section in the Application Hints  
section of this data sheet.  
1. Inductor Selection (L1) A. Use the selection guide  
shown in Figure 4. B. From the selection guide, the  
inductance area intersected by the 20V line and 0.8A line is  
L330. C. Inductor value required is 330 µH. From the table  
in Figure 9, choose AIE 415-0926, Pulse Engineering  
PE-52627, or RL1952.  
2. Output Capacitor Selection (COUT) A. The value of the  
output capacitor together with the inductor defines the  
dominate pole-pair of the switching regulator loop. For  
stable operation and an acceptable output ripple voltage,  
(approximately 1% of the output voltage) a value between  
100 µF and 470 µF is recommended. B. The capacitor’s  
voltage rating should be at least 1.5 times greater than the  
output voltage. For a 5V regulator, a rating of at least 8V is  
appropriate, and a 10V or 15V rating is recommended.  
Higher voltage electrolytic capacitors generally have lower  
ESR numbers, and for this reason it may be necessary to  
select a capacitor rated for a higher voltage than would  
normally be needed.  
2. Output Capacitor Selection (COUT) A. COUT = 100 µF  
to 470 µF standard aluminum electrolytic. B. Capacitor  
voltage rating = 20V.  
3. Catch Diode Selection (D1) A. The catch-diode current  
rating must be at least 1.2 times greater than the maximum  
load current. Also, if the power supply design must  
withstand a continuous output short, the diode should have  
a current rating equal to the maximum current limit of the  
LM2575. The most stressful condition for this diode is an  
overload or shorted output condition. B. The reverse voltage  
rating of the diode should be at least 1.25 times the  
maximum input voltage.  
3. Catch Diode Selection (D1) A. For this example, a 1A  
current rating is adequate. B. Use a 30V 1N5818 or SR103  
Schottky diode, or any of the suggested fast-recovery  
diodes shown in Figure 8.  
4. Input Capacitor (CIN) An aluminum or tantalum  
electrolytic bypass capacitor located close to the regulator is  
needed for stable operation.  
4. Input Capacitor (CIN) A 47 µF, 25V aluminum electrolytic  
capacitor located near the input and ground pins provides  
sufficient bypassing.  
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