![](http://datasheet.mmic.net.cn/30000/LM2575-15MWC_datasheet_2335475/LM2575-15MWC_13.png)
INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) (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
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
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
inductor code for that region.
E. Identify the inductor value from the inductor code, and
select an appropriate inductor from the table shown in
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 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.
LM1575/LM2575/LM2575HV
www.national.com
13