LM2671N-5.0 National Semiconductor, LM2671N-5.0 Datasheet - Page 18

• Manufacturer Part Number: LM2671N-5.0
• Description: DC/DC Converter IC
• Manufacturer: National Semiconductor

Specifications of LM2671N-5.0

• Input Voltage: 40V
• Output Current: 500mA
• Output Voltage: 5V
• No. Of Pins: 8
• Mounting Type: Through Hole
• Voltage Regulator Type: Buck Switching
• Output Current Max: 0.5A
• Peak Reflow Compatible (260 C): No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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5. Input Capacitor (C
A low ESR aluminum or tantalum bypass capacitor is needed
between the input pin and ground to prevent large voltage
transients from appearing at the input. This capacitor should
be located close to the IC using short leads. In addition, the
RMS current rating of the input capacitor should be selected to
be at least
data sheet must be checked to assure that this current rating
is not exceeded. The curves shown in Figure 14 show typical
RMS current ratings for several different aluminum electrolytic
capacitor values. A parallel connection of two or more
capacitors may be required to increase the total minimum RMS
current rating to suit the application requirements.
For an aluminum electrolytic capacitor, the voltage rating
should be at least 1.25 times the maximum input voltage.
Caution must be exercised if solid tantalum capacitors are
used. The tantalum capacitor voltage rating should be twice
the maximum input voltage. The tables in Figure 15 show the
recommended application voltage for AVX TPS and Sprague
594D tantalum capacitors. It is also recommended that they be
surge current tested by the manufacturer. The TPS series
available from AVX, and the 593D and 594D series from
Sprague are all surge current tested. Another approach to
minimize the surge current stresses on the input capacitor is to
add a small inductor in series with the input supply line.
Use caution when using ceramic capacitors for input
bypassing, because it may cause severe ringing at the V
6. Boost Capacitor (C
This capacitor develops the necessary voltage to turn the
switch gate on fully. All applications should use a 0.01 µF, 50V
ceramic capacitor.
If the soft-start and frequency synchronization features are
desired, look at steps 6 and 7 in the fixed output design
procedure.
LM2671 Series Buck Regulator Design Procedure (Adjustable Output)
Note 7: SM - Surface Mount, TH - Through Hole
(Continued)
Style (Note 7)
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
SM and TH
PROCEDURE (Adjustable Output Voltage Version)
Case
TH
1
⁄
2
the DC load current. The capacitor manufacturer
IN
B
Voltage (V)
)
1.21–2.50
2.50–3.75
10.0–12.5
12.5–15.0
15.0–20.0
20.0–30.0
30.0–37.0
)
3.75–5.0
5.0–6.25
6.25–7.5
7.5–10.0
Output
FIGURE 16. Capacitor Code Selection Guide
C14
C15
C18
C21
C23
C8
C9
22
—
—
—
—
C10
C11
C16
C19
C22
C24
C4
C4
33
—
—
—
IN
pin.
18
5. Input Capacitor (C
The important parameters for the input capacitor are the input
voltage rating and the RMS current rating. With a maximum
input voltage of 28V, an aluminum electrolytic capacitor with a
voltage rating of at least 35V (1.25 x V
The RMS current rating requirement for the input capacitor in a
buck regulator is approximately
example, with a 500 mA load, a capacitor with a RMS current
rating of at least 250 mA is needed. The curves shown in
Figure 14 can be used to select an appropriate input capacitor.
From the curves, locate the 35V line and note which capacitor
values have RMS current ratings greater than 250 mA.
For a through hole design, a 68 µF/35V electrolytic capacitor
(Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or
equivalent) would be adequate. Other types or other
manufacturers’ capacitors can be used provided the RMS
ripple current ratings are adequate. Additionally, for a complete
surface mount design, electrolytic capacitors such as the
Sanyo CV-C or CV-BS and the Nichicon WF or UR and the
NIC Components NACZ series could be considered.
For surface mount designs, solid tantalum capacitors can be
used, but caution must be exercised with regard to the
capacitor surge current rating and voltage rating. In this
example, checking Figure 15 , and the Sprague 594D series
datasheet, a Sprague 594D 15 µF, 50V capacitor is adequate.
6. Boost Capacitor (C
For this application, and all applications, use a 0.01 µF, 50V
ceramic capacitor.
C11
C12
C17
C20
C22
C24
C4
C7
C7
47
—
—
EXAMPLE (Adjustable Output Voltage Version)
Inductance (µH)
C12
C12
C17
C20
C22
C25
C1
C5
C6
C6
68
—
IN
B
)
)
C13
C13
C17
C20
C22
C25
100
C1
C2
C6
C6
C6
1
⁄
2
the DC load current. In this
IN
) would be needed.
C13
C13
C17
C20
C22
C25
150
C2
C3
C6
C6
C6
C13
C13
C17
C20
C22
C25
220
C3
C3
C6
C6
C6