LM2671MX-33 Datasheet, PDF (18/31 Pages) Texas Instruments – LM2671 SIMPLE SWITCHER Power Converter High Efficiency 500mA Step-Down Voltage

LM2671
SNVS008K – SEPTEMBER 1998 – REVISED APRIL 2013
Recommended
Application Voltage
Table 7. AVX TPS (continued)
Voltage
Rating
+85°C Rating
15
www.ti.com
35
Recommended
Application Voltage
Table 8. Sprague 594D
Voltage
Rating
+85°C Rating
2.5
4
3.3
6.3
5
10
8
16
12
20
18
25
24
35
29
50
LM2671 Series Buck Regulator Design Procedure (Adjustable Output)
PROCEDURE (Adjustable Output Voltage Version)
EXAMPLE (Adjustable Output Voltage Version)
To simplify the buck regulator design procedure, Texas Instrumnets
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:
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 260 kHz).
V_OUT = 20V
V_IN(max) = 28V
I_LOAD(max) = 500 mA
F = Switching Frequency (Fixed at a nominal 260 kHz).
1. Programming Output Voltage (Selecting R₁ and R₂, as shown in 1. Programming Output Voltage (Selecting R₁ and R₂, as shown in
Figure 23)
Figure 23)
Use the following formula to select the appropriate resistor values. Select R₁ to be 1 kΩ, 1%. Solve for R₂.
where V_REF = 1.21V
(3)
(4)
Select a value for R₁ between 240Ω and 1.5 kΩ. The lower 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.)
R₂ = 1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.
R₂ = 15.4 kΩ.
(5)
2. Inductor Selection (L1)
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant E • T (V • μs), A. Calculate the inductor Volt • microsecond constant (E • T),
from the following formula:
(6)
(7)
where V_SAT=internal switch saturation voltage=0.25V and V_D = diode
forward voltage drop = 0.5V
B. Use the E • T value from the previous formula and match it with B. E • T = 21.6 (V • μs)
the E • T number on the vertical axis of the Inductor Value Selection
Guide shown in Figure 27.
18
Submit Documentation Feedback
Product Folder Links: LM2671
Copyright © 1998–2013, Texas Instruments Incorporated