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LM2594M-ADJ 参数 Datasheet PDF下载

LM2594M-ADJ图片预览
型号: LM2594M-ADJ
PDF下载: 下载PDF文件 查看货源
内容描述: SIMPLE SWITCHER系列电源转换器150千赫0.5A降压稳压器 [SIMPLE SWITCHER Power Converter 150 kHz 0.5A Step-Down Voltage Regulator]
分类和应用: 转换器稳压器开关式稳压器或控制器电源电路开关式控制器光电二极管PC
文件页数/大小: 28 页 / 742 K
品牌: NSC [ National Semiconductor ]
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LM2594/LM2594HV Series Buck Regulator Design Procedure (Adjustable  
Output) (Continued)  
PROCEDURE (Adjustable Output Voltage Version)  
EXAMPLE (Adjustable Output Voltage Version)  
1. Programming Output Voltage (Selecting R1 and R2, as  
1. Programming Output Voltage (Selecting R1 and R2, as  
shown in Figure 1.  
shown in Figure 1 )  
Use the following formula to select the appropriate resistor  
values.  
Select R1 to be 1 k, 1%. Solve for R2.  
=
=
R2 1k (16.26 − 1) 15.26k, closest 1% value is 15.4 k.  
Select a value for R1 between 240and 1.5 k. The lower  
resistor values minimize noise pickup in the sensitive feed-  
back pin. (For the lowest temperature coefficient and the best  
stability with time, use 1% metal film resistors.)  
=
R2 15.4 k.  
2. Inductor Selection (L1)  
2. Inductor Selection (L1)  
A. Calculate the inductor Volt microsecond constant  
A. Calculate the inductor Volt microsecond constant (E T)  
E T (V µs) , from the following formula:  
,
=
=
where VSAT internal switch saturation voltage 0.9V  
=
=
and VD diode forward voltage drop 0.5V  
B. Use the E T value from the previous formula and match  
it with the E T number on the vertical axis of the Inductor  
Value Selection Guide shown in Figure 7.  
=
B. E T 35.2 (V µs)  
=
C. ILOAD(max) 0.5A  
D. From the inductor value selection guide shown in Figure 7,  
the inductance region intersected by the 35 (V µs) horizon-  
tal line and the 0.5A vertical line is 150 µH, and the inductor  
code is L19.  
C. on the horizontal axis, select the maximum load current.  
D. Identify the inductance region intersected by the E T  
value and the Maximum Load Current value. Each region is  
identified by an inductance value and an inductor code  
(LXX).  
E. From the table in Figure 8, locate line L19, and select an  
inductor part number from the list of manufacturers part num-  
bers.  
E. Select an appropriate inductor from the four manufactur-  
er’s part numbers listed in Figure 8.  
3. Output Capacitor Selection (COUT)  
3. Output Capacitor SeIection (COUT)  
A. In the majority of applications, low ESR electrolytic or solid  
tantalum capacitors between 82 µF and 220 µF provide the  
best results. This capacitor should be located close to the IC  
using short capacitor leads and short copper traces. Do not  
use capacitors larger than 220 µF. For additional informa-  
tion, see section on output capacitors in application in-  
formation section.  
A. See section on COUT in Application Information section.  
B. From the quick design table shown in Figure 3, locate the  
output voltage column. From that column, locate the output  
voltage closest to the output voltage in your application. In  
this example, select the 24V line. Under the output capacitor  
section, select a capacitor from the list of through hole elec-  
trolytic or surface mount tantalum types from four different  
capacitor manufacturers. It is recommended that both the  
manufacturers and the manufacturers series that are listed in  
the table be used.  
B. To simplify the capacitor selection procedure, refer to the  
quick design table shown in Figure 3. This table contains dif-  
ferent output voltages, and lists various output capacitors  
that will provide the best design solutions.  
In this example, through hole aluminum electrolytic capaci-  
tors from several different manufacturers are available.  
C. The capacitor voltage rating should be at least 1.5 times  
greater than the output voltage, and often much higher volt-  
age ratings are needed to satisfy the low ESR requirements  
needed for low output ripple voltage.  
82 µF 50V Panasonic HFQ Series  
120 µF 50V Nichicon PL Series  
C. For a 20V output, a capacitor rating of at least 30V or  
more is needed. In this example, either a 35V or 50V capaci-  
tor would work. A 50V rating was chosen because it has a  
lower ESR which provides a lower output ripple voltage.  
Other manufacturers or other types of capacitors may also  
be used, provided the capacitor specifications (especially the  
100 kHz ESR) closely match the types listed in the table. Re-  
fer to the capacitor manufacturers data sheet for this informa-  
tion.  
www.national.com  
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