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| 型号： | LM2597-3.3MWA |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1.4 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, UUC |
| 封装： | WAFER |
| 文件页数： | 4/40页 |
| 文件大小： | 1019K |
| 代理商： | LM2597-3.3MWA |
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LM2597/LM2597HV Series Buck Regulator Design Procedure (Adjustable
Output)
PROCEDURE (Adjustable Output Voltage Version)
EXAMPLE (Adjustable Output Voltage Version)
Given:
V
OUT = Regulated Output Voltage
V
IN(max) = Maximum Input Voltage
I
LOAD(max) = Maximum Load Current
F = Switching Frequency
(Fixed at a nominal 150 kHz).
Given:
V
OUT = 20V
V
IN(max) = 28V
I
LOAD(max) = 0.5A
F = Switching Frequency
(Fixed at a nominal 150 kHz).
1. Programming Output Voltage (Selecting R
1 and R2,as
shown in
Figure 12)
Use the following formula to select the appropriate resistor
values.
Select a value for R
1 between 240 and 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.)
1. Programming Output Voltage (Selecting R
1 and R2,as
shown in
Figure 12)
Select R
1 to be 1 k, 1%. Solve for R2.
R
2 = 1k (16.26 1) = 15.26k, closest 1% value is 15.4 k.
R
2 = 15.4 k.
2. Inductor Selection (L1)
A. Calculate the inductor Volt microsecond constant E
T
(V
s), from the following formula:
where V
SAT = internal switch saturation voltage = 0.9V
and V
D = 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 6.
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. Select an appropriate inductor from the four manufacturer’s
part numbers listed in
Figure 7.
2. Inductor Selection (L1)
A. Calculate the inductor Volt
microsecond constant (E T),
B. E
T = 35.2 (V s)
C. I
LOAD(max) = 0.5A
D. From the inductor value selection guide shown in
Figure 6,
the inductance region intersected by the 35 (V
s) horizontal
line and the 0.5A vertical line is 150 H, and the inductor code
is L19.
E. From the table in
Figure 7, locate line L19, and select an
inductor part number from the list of manufacturers part num-
bers.
LM2597/LM2597HV
www.national.com
12
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