lm2675ldx-12 National Semiconductor Corporation, lm2675ldx-12 Datasheet - Page 17

• Manufacturer Part Number: lm2675ldx-12
• Description: Simple Switcher Power Converter High Efficiency 1a Step-down Voltage Regulator
• Manufacturer: National Semiconductor Corporation

To simplify the buck regulator design procedure, National
Semiconductor is making available computer design software to
be used with the SIMPLE SWITCHER line of switching
regulators. LM267X Made Simple version 6.0 is available for
use on Windows 3.1, NT, or 95 operating systems.
Given:
1. Programming Output Voltage (Selecting R
shown in Figure 3)
Use the following formula to select the appropriate resistor
values.
Select a value for R
resistor values minimize noise pickup in the sensitive feedback
pin. (For the lowest temperature coefficient and the best stability
with time, use 1% metal film resistors.)
where V
LM2675 Series Buck Regulator Design Procedure (Fixed Output)
LM2675 Series Buck Regulator Design Procedure (Adjustable Output)
V
V
I
F = Switching Frequency (Fixed at a nominal 260 kHz).
LOAD
OUT
IN
(max) = Maximum Input Voltage
PROCEDURE (Adjustable Output Voltage Version)
(max) = Maximum Load Current
= Regulated Output Voltage
REF
= 1.21V
1
between 240Ω and 1.5 kΩ. The lower
Recommended
Application Voltage
Recommended
Application Voltage
1
and R
2
3.3
2.5
3.3
10
12
15
12
18
24
29
, as
5
5
8
Sprague 594D
+85˚C Rating
+85˚C Rating
FIGURE 15.
AVX TPS
17
Given:
1. Programming Output Voltage (Selecting R
shown in Figure 3)
Select R
R
R
2
2
V
V
I
F = Switching Frequency (Fixed at a nominal 260 kHz).
LOAD
= 1k (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.
= 15.4 kΩ.
OUT
IN
Voltage
Rating
Voltage
Rating
(max) = 28V
EXAMPLE (Adjustable Output Voltage Version)
(max) = 1A
= 20V
1
to be 1 kΩ, 1%. Solve for R
6.3
6.3
10
20
25
35
10
16
20
25
35
50
4
2
.
1
(Continued)
and R
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2
, as