参数资料
型号: LM1575J-CAD/883
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: 稳压器
英文描述: 3.2 A SWITCHING REGULATOR, 62 kHz SWITCHING FREQ-MAX, CDIP16
封装: CERDIP-16
文件页数: 5/30页
文件大小: 676K
代理商: LM1575J-CAD/883
(Continued)
PROCEDURE (Adjustable Output Voltage Versions)
EXAMPLE (Adjustable Output Voltage Versions)
Given:
V
OUT = Regulated Output Voltage
V
IN(Max) = Maximum Input Voltage
I
LOAD(Max) = Maximum Load Current
F = Switching Frequency
(Fixed at 52 kHz)
Given:
V
OUT = 10V
V
IN(Max) = 25V
I
LOAD(Max) = 1A
F = 52 kHz
1. Programming Output Voltage
(Selecting R1 and R2, as
shown in Figure 2 )
Use the following formula to select the appropriate resistor
values.
R
1 can be between 1k and 5k. (For best temperature coeffi-
cient and stability with time, use 1% metal film resistors)
1.Programming Output Voltage
(Selecting R1 and R2)
R2 = 1k (8.13 1) = 7.13k, closest 1% value is 7.15k
2. Inductor Selection (L1)
A. Calculate the inductor Volt
microsecond constant,
E
T(V s), from the following formula:
B. Use the E
T value from the previous formula and match
it with the E
T number on the vertical axis of the Inductor
Value Selection Guide shown in
Figure 7.
C. On the horizontal axis, select the maximum load current.
D. Identify the inductance region intersected by the E
T
value and the maximum load current value, and note the in-
ductor code for that region.
E. Identify the inductor value from the inductor code, and se-
lect 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 rat-
ing of 1.15 x I
LOAD. For additional inductor information, see
the inductor section in the application hints section of this
data sheet.
2. Inductor Selection (L1)
A. Calculate E
T(V s)
B. E
T = 115 V s
C. I
LOAD(Max) = 1A
D. Inductance Region = H470
E. Inductor Value = 470 H
Choose from AIE part
#430-0634, Pulse Engineering part #PE-53118, or Renco
part #RL-1961.
www.national.com
13
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