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LTC3100

3100fa

APPLICATIONS INFORMATION

COMPONENT SELECTION

Boost Output Voltage Programming

The boost output voltage is set by a resistive divider ac-

cording to the following formula:

OUT =+

⎛

⎝⎜

⎞

⎠⎟

1 200

.•

The external divider is connected to the output as shown

in the Block Diagram. A feedforward capacitor may be

placed in parallel with resistor R2 to improve the noise

immunity of the feedback node, improve transient response

and reduce output ripple in Burst Mode operation. A value

of 33pF will generally sufﬁce.

Boost Inductor Selection

The LTC3100 boost converter can utilize small surface

mount and chip inductors due to the fast 1.5MHz switch-

ing frequency. Inductor values between 2.2μH and 4.7μH

are suitable for most applications. Larger values of induc-

tance will allow slightly greater output current capability

by reducing the inductor ripple current. Increasing the

inductance above 10μH will increase size while providing

little improvement in output current capability.

The minimum boost inductance value is given by:

RIPPLE V

IN MIN

OUT MAX

IN MIN

−

()

(

)

()

•

.•

•

OUT MAX

()

Where:

RIPPLE = Allowable Inductor Current Ripple (Amps Peak-

to-Peak)

VIN(MIN) = Minimum Input Voltage

VOUT(MAX) = Maximum Output Voltage

The inductor current ripple is typically set for 20% to

40% of the maximum inductor current. High frequency

ferrite core inductor materials reduce frequency dependent

power losses compared to cheaper powdered iron types,

improving efﬁciency. The inductor should have low DCR

(series resistance of the winding) to reduce the I2R power

losses, and must not saturate at peak inductor current

levels. Molded chokes and some chip inductors usually

do not have enough core area to support the peak induc-

tor currents of 800mA seen on the LTC3100. To minimize

radiated noise, use a shielded inductor. See Table 1 for

suggested components and suppliers.

Table 1. Recommended Boost Inductors

VENDOR

PART/STYLE

Coilcraft

(847) 639-6400

www.coilcraft.com

LPS4012, LPS4018

MSS4020, MSS5131

Coiltronics

SD14, SD3814, SD3118

FDK

MIPSA2520

MIPW3226

Murata

www.murata.com

LQH43C

Sumida

(847) 956-0666

www.sumida.com

CDRH2D18, CDRH2D16

CDRH3D14, CDRH3D16

CDRH4D14, CDRH4D16

Taiyo-Yuden

www.t-yuden.com

NR3015

NP03SB

TDK

www.tdk.com

VLP

VLF, VLCF

Toko

(408) 432-8282

www.tokoam.com

D518LC

D52LC

DP418C

Würth

(201) 785-8800

www.we-online.com

WE-TPC Type S, M

Boost Input and Output Capacitor Selection

The internal loop compensation of the LTC3100 boost con-

verter is designed to be stable with output capacitor values

of 4.7μF or greater. Low ESR (equivalent series resistance)

capacitors should be used to minimize the output voltage

ripple. Multilayer ceramic capacitors are an excellent choice

as they have extremely low ESR and are available in small

footprints. A 4.7μF to 10μF output capacitor is sufﬁcient

for most ﬁxed frequency applications. For applications

where Burst Mode operation is enabled, a minimum value

of 20μF is recommended. Larger values may be used to

obtain very low output ripple and to improve transient

response. X5R and X7R dielectric materials are preferred

for their ability to maintain capacitance over wide voltage

and temperature ranges. Y5V types should not be used.

Case sizes smaller than 0805 are not recommended due

to their increased DC bias effect.

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