LM2674N-3.3 National Semiconductor, LM2674N-3.3 Datasheet - Page 16

• Manufacturer Part Number: LM2674N-3.3
• Description: DC/DC Converter IC
• Manufacturer: National Semiconductor

Specifications of LM2674N-3.3

• Input Voltage: 40V
• Output Current: 500mA
• Output Voltage: 3.3V
• No. Of Pins: 8
• Mounting Type: Through Hole
• Voltage Regulator Type: Switching
• Output Current Max: 500mA
• Peak Reflow Compatible (260 C): No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant E • T (V
where V
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 7 .
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 8 . For information on the different
types of inductors, see the inductor selection in the fixed
output voltage design procedure.
3. Output Capacitor Selection (C
A. Select an output capacitor from the capacitor code selection
guide in Figure 16 . Using the inductance value found in the
inductor selection guide, step 1, locate the appropriate
capacitor code corresponding to the desired output voltage.
B. Select an appropriate capacitor value and voltage rating,
using the capacitor code, from the output capacitor selection
table in Figure 17 . There are two solid tantalum (surface
mount) capacitor manufacturers and four electrolytic (through
hole) capacitor manufacturers to choose from. It is
recommended that both the manufacturers and the
manufacturer’s series that are listed in the table be used. A
table listing the manufacturers’ phone numbers is located in
Figure 11 .
• µs), from the following formula:
= diode forward voltage drop = 0.5V
LM2674 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
PROCEDURE (Adjustable Output Voltage Version)
SAT
= internal switch saturation voltage = 0.25V and V
OUT
)
D
16
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant (E • T),
B. E • T = 21.6 (V • µs)
C. I
D. From the inductor value selection guide shown in Figure 7 ,
the inductance region intersected by the 21.6 (V • µs)
horizontal line and the 500mA vertical line is 100 µH, and the
inductor code is L20.
E. From the table in Figure 8 , locate line L20, and select an
inductor part number from the list of manufacturers part
numbers.
3. Output Capacitor SeIection (C
A. Use the appropriate row of the capacitor code selection
guide, in Figure 16 . For this example, use the 15–20V row.
The capacitor code corresponding to an inductance of 100 µH
is C20.
B. From the output capacitor selection table in Figure 17 ,
choose a capacitor value (and voltage rating) that intersects
the capacitor code(s) selected in section A, C20.
The capacitance and voltage rating values corresponding to
the capacitor code C20 are the:
Surface Mount:
33 µF/25V Sprague 594D Series.
33 µF/25V AVX TPS Series.
Through Hole:
33 µF/25V Sanyo OS-CON SC Series.
120 µF/35V Sanyo MV-GX Series.
120 µF/35V Nichicon PL Series.
120 µF/35V Panasonic HFQ Series.
Other manufacturers or other types of capacitors may also be
used, provided the capacitor specifications (especially the 100
kHz ESR) closely match the characteristics of the capacitors
listed in the output capacitor table. Refer to the capacitor
manufacturers’ data sheet for this information.
LOAD
EXAMPLE (Adjustable Output Voltage Version)
(max) = 500 mA
OUT
)