LM2671LD-12 NSC [National Semiconductor], LM2671LD-12 Datasheet - Page 17

• Manufacturer Part Number: LM2671LD-12
• Description: SIMPLE SWITCHER Power Converter High Efficiency 500mA Step-Down Voltage Regulator with Features
• Manufacturer: NSC [National Semiconductor]

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 is available on (version 6.0)
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.)
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant E • T
(V • µs), from the following formula:
where V
V
where V
D
LM2671 Series Buck Regulator Design Procedure (Fixed Output)
LM2671 Series Buck Regulator Design Procedure (Adjustable Output)
V
V
I
F = Switching Frequency (Fixed at a nominal 260 kHz).
LOAD
= diode forward voltage drop = 0.5V
OUT
IN
(max) = Maximum Input Voltage
PROCEDURE (Adjustable Output Voltage Version)
(max) = Maximum Load Current
= Regulated Output Voltage
SAT
REF
Recommended
Application Voltage
=internal switch saturation voltage=0.25V and
= 1.21V
1
3.3
between 240Ω and 1.5 kΩ. The lower
10
12
15
5
+85˚C Rating
AVX TPS
FIGURE 15. Recommended Application Voltage for AVX TPS and
Sprague 594D Tantalum Chip Capacitors Derated for 85˚C.
Voltage
Rating
6.3
10
20
25
35
1
and R
2
, as
17
Given:
1. Programming Output Voltage (Selecting R
shown in Figure 3)
Select R
R
R
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant (E • T),
2
2
V
V
I
F = Switching Frequency (Fixed at a nominal 260 kHz).
LOAD
= 1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.
= 15.4 kΩ.
OUT
IN
(max) = 28V
EXAMPLE (Adjustable Output Voltage Version)
Recommended
Application Voltage
(max) = 500 mA
= 20V
1
to be 1 kΩ, 1%. Solve for R
2.5
3.3
12
18
24
29
5
8
Sprague 594D
+85˚C Rating
Voltage
Rating
2
.
6.3
10
16
20
25
35
50
4
1
(Continued)
and R
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2
, as