LTC3556_15 datasheet(27/36 Pages) LINER

27 / 36 page

LTC3556

3556f

APPLICATIONS INFORMATION

400mA Step-Down Switching Regulator Input/Output

Capacitor Selection

Low ESR (equivalent series resistance) MLCC capacitors

should be used at both buck regulator outputs as well as at

each buck regulator input supply (VIN1 and VIN2). Only X5R

or X7R ceramic capacitors should be used because they

retain their capacitance over wider voltage and temperature

ranges than other ceramic types. A 10μF output capaci-

tor is sufﬁcient for most applications. For good transient

response and stability the output capacitor should retain

at least 4μF of capacitance over operating temperature

and bias voltage. Each buck regulator input supply should

be bypassed with a 1μF capacitor. Consult with capacitor

manufacturers for detailed information on their selection

and speciﬁcations of ceramic capacitors. Many manufac-

turers now offer very thin (<1mm tall) ceramic capacitors

ideal for use in height-restricted designs. Table 8 shows a

list of several ceramic capacitor manufacturers.

Table 8. Recommended Ceramic Capacitor Manufacturers

AVX

www.avxcorp.com

Murata

www.murata.com

Taiyo Yuden

www.t-yuden.com

Vishay Siliconix

www.vishay.com

TDK

www.tdk.com

Buck-Boost Regulator Inductor Selection

Inductor selection criteria for the buck-boost are similar to

those given for the 400mA step-down switching regulators.

The buck-boost converter is designed to work with induc-

tors in the range of 1μH to 5μH. For most applications a

2.2μH inductor will sufﬁce. Choose an inductor with a DC

current rating at least 2 times larger than the maximum

load current to ensure that the inductor does not saturate

during normal operation. If output short circuit is a pos-

sible condition, the inductor should be rated to handle

the maximum peak current speciﬁed for the buck-boost

converter.

Table 9 shows several inductors that work well with the

LTC3556’s buck-boost regulator. These inductors offer a

good compromise in current rating, DCR and physical

size. Consult each manufacturer for detailed information

on their entire selection of inductors.

Table 9. Recommended Inductors for Buck-Boost Regulator

INDUCTOR

TYPE

(μH)

MAX

IDC

(A)

MAX

DCR

(Ω)

SIZE IN mm

× W × H) MANUFACTURER

LPS4018

3.3

2.2

2.5

0.08

0.07

3.9

× 3.9 × 1.7

3.9

× 3.9 × 1.7

Coilcraft

www.coilcraft.com

D53LC

2.0

3.25

0.02

5.0

× 5.0 × 3.0 Toko

www.toko.com

7440430022

2.2

2.5

0.028 4.8

× 4.8 × 2.8 Würth-Elektronik

www.we-online.com

CDRH4D22/

2.2

2.4

0.044 4.7

× 4.7 × 2.4 Sumida

www.sumida.com

SD14

2.0

2.56 0.045

5.2

× 5.2 ×

1.45

Cooper

www.cooperet.com

Buck-Boost Regulator Input/Output Capacitor

Selection

Low ESR MLCC capacitors should also be used at both the

buck-boost regulator output (VOUT3) and the buck-boost

regulator input supply (VIN3). Again, only X5R or X7R ce-

ramic capacitors should be used because they retain their

capacitance over wider voltage and temperature ranges

than other ceramic types. A 22μF output capacitor is suf-

ﬁcient for most applications. The buck-boost regulator

input supply should be bypassed with a 2.2μF capacitor.

Refer to Table 8 for recommended ceramic capacitor

manufacturers.

Buck-Boost Regulator Output Voltage Programming

The buck-boost regulator can be programmed for output

voltages greater than 2.75V and less than 5.5V. The full-

scale output voltage is programmed using a resistor divider

from the VOUT3 pin connected to the FB3 pin such that:

OUT

⎛

⎝⎜

⎞

⎠⎟

where VFB3 ranges from 0.425V to 0.8V.

LTC3556 датащи(PDF) 27 Page - Linear Technology

LTC3556 датащи(HTML) 27 Page - Linear Technology

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 32 33 34 35 36

датащи скачать

ссылки URL