LTC3129 datasheet(22/34 Pages) AD

22 / 34 page

LTC3114-1

Rev. D

For more information www.analog.com

APPLICATIONS INFORMATION

the series resistance of the output capacitor and all other

terms as previously defined.

ΔVP-P(BUCK) =

ILOADRESR

1– tLOWf

≅ ILOADRESR Volts

ΔVP-P(BOOST) =

ILOADRESRVOUT

VIN 1– tLOWf

(

)

≅ ILOADRESR

VOUT

VIN

⎛

⎝⎜

⎞

⎠⎟

Volts

In most LTC3114-1 applications, an output capacitor

between 10µF and 22µF will work well.

Input Capacitor Selection

The PVIN pin carries the full inductor current and provides

power to internal control circuits in the IC. To minimize

input voltage ripple and ensure proper operation of the IC,

a low ESR bypass capacitor with a value of at least 6.8µF

should be located as close to the pin as possible. The

traces connecting this capacitor to PVIN and the ground

plane should be made as short as possible. The VIN pin

provides power to the LDO regulator and other internal

circuitry. If the PCB trace connecting PVIN to VIN is long, it

is recommended to add an additional small 0.1µF bypass

capacitor near the VIN pin.

When powered through long leads or from a high ESR

power source, a larger value bulk input capacitor may

be required. In such applications, a 47µF to 100µF elec-

trolytic capacitor in parallel with a 1µF ceramic capacitor

generally yields a high performance, low cost solution.

Recommended Input and Output Capacitors

The capacitors used to filter the input and output of the

LTC3114-1 must have low ESR and must be rated to han-

dle the large AC currents generated by the switching con-

verters. This is important to maintain proper functioning of

the IC and to reduce output voltage ripple. There are many

capacitor types that are well suited to these applications

including multilayer ceramic, low ESR tantalum, OS-CON

and POSCAP technologies. In addition, there are certain

types of electrolytic capacitors such as solid aluminum

organic polymer capacitors that are designed for low ESR

and high AC currents and these are also well suited to some

LTC3114-1 applications. Table 2 provides a partial listing

of appropriate capacitors to use with the LTC3114-1. The

choice of capacitor technology is primarily dictated by a

trade-off between size, leakage current and cost. In backup

power applications, the input or output capacitor might be

a super or ultra capacitor with a capacitance value mea-

suring in the Farad range. The selection criteria in these

Table 2. Representative Bypass and Output Capacitors

MANUFACTURER,

PART NUMBER

VALUE

(µF)

VOLTAGE

(V)

SIZE L × W × H (mm),

TYPE, ESR

AVX

12103D226MAT2A

3.2 × 2.5 × 2.79

X5R Ceramic

TPME226K050R0075

7.3 × 4.3 × 4.1

Tantalum, 75mΩ

Kemet

C2220X226K3RACTU

5.7 × 5.0 × 2.4

X7R Ceramic

A700D226M016ATE030

7.3 × 4.3 × 2.8

Alum. Polymer, 30mΩ

Murata

GRM32ER71E226KE15L

3.2 × 2.5 × 2.5

X7R Ceramic

Nichicon

PLV1E121MDL1

8 × 8 × 12

Alum. Polymer, 25mΩ

Panasonic

ECJ-4YB1E226M

3.2 × 2.5 × 2.5

X5R Ceramic

Sanyo

25TQC22MV

7.3 × 4.3 × 3.1

POSCAP, 50mΩ

16TQC100M

100

7.3 × 4.3 × 1.9

POSCAP, 45mΩ

25SVPF47M

6.6 × 6.6 × 5.9

OS-CON, 30mΩ

Taiyo Yuden

UMK325BJ106MM-T

3.2 × 2.5 × 2.5

X5R Ceramic

TMK325BJ226MM-T

3.2 × 2.5 × 2.5

X5R Ceramic

TDK

KTJ500B226M55BFT00

6.0 × 5.3 × 5.5

X7R Ceramic

C5750X7R1H106M

5.7 × 5.0 × 2.0

X7R Ceramic

CKG57NX5R1E476M

6.5 × 5.5 × 5.5

X5R Ceramic

Vishay

94SVPD476X0035F12

10.3 × 10.3 × 12.6

OS-CON, 30mΩ

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