LTC3113 datasheet(13/24 Pages) LINER

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LTC3113

3113f

APPLICATIONS INFORMATION

The choice of inductor style depends upon the price, sizing,

and EMI requirements of a particular application. Table 1

provides a small sampling of inductors that are well suited

to many LTC3113 buck-boost converter applications. All

inductor speciﬁcations are listed at an inductance value

of 2.2μH for comparison purposes but other values within

these inductor families are generally well suited to this

application. Within each family (i.e. at a ﬁxed size), the DC

resistance generally increases and the maximum current

generally decreases with increased inductance.

Table 1. Representative Buck-Boost Surface Mount Inductors

PART

NUMBER

VALUE

(μH)

DCR

(mΩ)

MAX DC

CURRENT (A)

SIZE (mm)

× L × H

CoilCraft (www.coilcraft.com)

MSS1048

2.2

7.2

8.4

× 10.3 × 4

MSS1260

2.2

13.9

12.3

× 12.3 × 6

SER1052

2.2

10.6

× 10.6 × 5.2

Toko (www.toko.com)

D106C

2.4

7.7

10.3

× 10.3 × 6.7

FDA1055

2.2

4.8

10.5

11.6

× 10.8 × 5.5

FDA1254

2.2

4.5

14.7

13.5

× 12.6 × 5.4

Cooper (www.cooperbussmann.com)

HCP0703

2.2

× 7.3 × 3

HCP0704

2.3

16.5

11.5

6.8

× 6.8 × 4.2

HC8

2.6

11.4

10.9

× 10.4 × 4

TDK (www.component.tdk.com)

VLF100040

2.2

7.9

8.2

9.7

× 10 × 4

RLF12560

2.7

4.5

× 13 × 6

VLF12060

2.7

6.4

11.7

× 12 × 6

Wurth (www.we-online.com)

744066

2.2

10.5

6.8

× 10 × 3.8

744355

13.2

× 12.8 × 6.2

744324

2.4

4.8

10.5

× 10.2 × 4.7

OUTPUT CAPACITOR SELECTION

A low ESR output capacitor should be utilized at the buck-

boost converter output in order to minimize output voltage

ripple. Multilayer ceramic capacitors are an excellent choice

as they have low ESR and are available in small footprints.

The capacitor should be chosen large enough to reduce the

output voltage ripple to acceptable levels. Neglecting the

capacitor ESR and ESL, the peak-to-peak output voltage

ripple can be calculated by the following formulas, where

f is the frequency in MHz, COUT is the capacitance in μF, L

is the inductance in μH, VIN is the input voltage in volts,

VOUT is the output voltage in volts. ∆VP-P is the output

ripple in volts and ILOAD is the output current in amps.

OUT ≥

ΔV

P-P,BUCK •8 •L• f

•

IN –VOUT

()•V

OUT

µF

()

OUT ≥

LOAD VOUT –VIN

()

ΔV

P-P,BOOST •VOUT •f

µF

()

Given that the output current is discontinuous in boost

mode, the ripple in this mode will generally be much larger

than the magnitude of the ripple in buck mode.

INPUT CAPACITOR SELECTION

It is recommended that a low ESR ceramic capacitor with a

value of at least 47μF be located as close to VIN as possible.

In addition, the return trace from the pin to the ground

plane should be made as short as possible. It is important

to minimize any stray resistance from the converter to the

battery or other power sources. If cabling is required to

connect the LTC3113 to the battery or power supply, a higher

ESR capacitor or a series resistor with low ESR capacitor

in parallel with the low ESR capacitor may be needed to

damp out ringing caused by the cable inductance.

CAPACITOR VENDOR INFORMATION

Both the input bypass capacitors and output capacitors

used with the LTC3113 must be low ESR and designed

to handle the large AC currents generated by switching

converters. This is important to maintain proper functioning

of the IC and to reduce output ripple. Many modern low

voltage ceramic capacitors experience signiﬁcant loss in

capacitance from their rated value with increased DC bias

voltages. For example, it is not uncommon for a small

surface mount ceramic capacitor to lose 50% or more

of its rated capacitance when operated near its rated

voltage. As a result, it is sometimes necessary to use

a larger value capacitance or a capacitor with a higher

voltage rating than required in order to actually realize

the intended capacitance at the full operating voltage. For

details, consult the capacitor vendor’s curve of capacitance

versus DC bias voltage.

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