LM2671LD-ADJ datasheet(20/31 Pages) TI

20 / 31 page

LM2671

SNVS008K – SEPTEMBER 1998 – REVISED APRIL 2013

www.ti.com

PROCEDURE (Adjustable Output Voltage Version)

EXAMPLE (Adjustable Output Voltage Version)

5. Input Capacitor (CIN)

A low ESR aluminum or tantalum bypass capacitor is needed

The important parameters for the input capacitor are the input

between the input pin and ground to prevent large voltage transients

voltage rating and the RMS current rating. With a maximum input

from appearing at the input. This capacitor should be located close

voltage of 28V, an aluminum electrolytic capacitor with a voltage

to the IC using short leads. In addition, the RMS current rating of the

rating of at least 35V (1.25 × VIN) would be needed.

input capacitor should be selected to be at least ½ the DC load

The RMS current rating requirement for the input capacitor in a buck

current. The capacitor manufacturer data sheet must be checked to

regulator is approximately ½ the DC load current. In this example,

assure that this current rating is not exceeded. The curves shown in

with a 500 mA load, a capacitor with a RMS current rating of at least

Figure 28 show typical RMS current ratings for several different

250 mA is needed. The curves shown in Figure 28 can be used to

aluminum electrolytic capacitor values. A parallel connection of two

select an appropriate input capacitor. From the curves, locate the

or more capacitors may be required to increase the total minimum

35V line and note which capacitor values have RMS current ratings

RMS current rating to suit the application requirements.

greater than 250 mA.

For an aluminum electrolytic capacitor, the voltage rating should be

For a through hole design, a 68

μF/35V electrolytic capacitor

at least 1.25 times the maximum input voltage. Caution must be

(Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or

exercised if solid tantalum capacitors are used. The tantalum

equivalent) would be adequate. Other types or other manufacturers'

capacitor voltage rating should be twice the maximum input voltage.

capacitors can be used provided the RMS ripple current ratings are

The tables in Recommended Application Voltage for AVX TPS and

adequate. Additionally, for a complete surface mount design,

Sprague 594D Tantalum Chip Capacitors Derated for 85°C. show

electrolytic capacitors such as the Sanyo CV-C or CV-BS and the

the recommended application voltage for AVX TPS and Sprague

Nichicon WF or UR and the NIC Components NACZ series could be

594D tantalum capacitors. It is also recommended that they be surge considered.

current tested by the manufacturer. The TPS series available from

For surface mount designs, solid tantalum capacitors can be used,

AVX, and the 593D and 594D series from Sprague are all surge

but caution must be exercised with regard to the capacitor surge

current tested. Another approach to minimize the surge current

current rating and voltage rating. In this example, checking

stresses on the input capacitor is to add a small inductor in series

Recommended Application Voltage for AVX TPS and Sprague 594D

with the input supply line.

Tantalum Chip Capacitors Derated for 85°C., and the Sprague 594D

Use caution when using ceramic capacitors for input bypassing,

series datasheet, a Sprague 594D 15

μF, 50V capacitor is adequate.

because it may cause severe ringing at the VIN pin.

6. Boost Capacitor (CB)

This capacitor develops the necessary voltage to turn the switch

For this application, and all applications, use a 0.01

μF, 50V ceramic

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.

Table 9. Capacitor Code Selection Guide

Inductance (

μH)

Case

Output

Style (1)

Voltage (V)

100

150

220

SM and TH

1.21–2.50

—

SM and TH

2.50–3.75

—

SM and TH

3.75–5.0

—

SM and TH

5.0–6.25

—

SM and TH

6.25–7.5

SM and TH

7.5–10.0

C10

C11

C12

C13

SM and TH

10.0–12.5

C14

C11

C12

C13

SM and TH

12.5–15.0

C15

C16

C17

SM and TH

15.0–20.0

C18

C19

C20

SM and TH

20.0–30.0

C21

C22

30.0–37.0

C23

C24

C25

(1)

SM - Surface Mount, TH - Through Hole

Table 10. Output Capacitor Selection Table

Output Capacitor

Surface Mount

Through Hole

Cap.

Sprague

AVX TPS

Sanyo OS-CON

Sanyo MV-GX

Nichicon

Panasonic

Ref.

Desg.

594D Series

Series

SA Series

Series

PL Series

HFQ Series

(

μF/V)

(

μF/V)

(

μF/V)

(

μF/V)

(

μF/V)

(

μF/V)

120/6.3

100/10

220/35

120/6.3

100/10

150/35

Submit Documentation Feedback

Product Folder Links: LM2671

LM2671LD-ADJ Datasheet(PDF) 20 Page - Texas Instruments

LM2671LD-ADJ Datasheet(HTML) 20 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Datasheet Download

Link URL