10

LTC3403

3403f

Table 1. Representative Surface Mount Inductors

Part

Value

DCR

MAX DC

Size

Number

(

µH)

(

ΩMAX)

Current (A)

Sumida

1.5

0.068

0.90

3.2 x 3.2 x 1.2

CDRH2D11

2.2

0.098

0.78

3.3

0.123

0.60

Sumida

2.2

0.041

0.85

3.2 x 3.2 x 2.0

CDRH2D18/LD

3.3

0.054

0.75

4.7

0.078

0.63

Sumida

2.2

0.116

0.95

3.5 x 4.1 x 0.8

CMD4D06

3.3

0.174

0.77

4.7

0.216

0.75

Murata

1.0

0.060

1.00

2.5 x 3.2 x 2.0

LQH32C

2.2

0.097

0.79

4.7

0.150

0.65

Taiyo Yuden

1.0

0.080

0.78

1.8 x 2.5 x 1.8

LQLBC2518

1.5

0.110

0.66

2.2

0.130

0.60

Toko

2.2

0.14

1.14

4.6 x 4.6 x 1.2

D412F

3.3

0.20

0.90

4.7

0.22

0.80

In continuous mode, the source current of the top MOSFET

voltage transients, a low ESR input capacitor sized for the

maximum RMS current must be used. The maximum

RMS capacitor current is given by:

C

required I

I

VV

V

V

IN

RMS

OMAX

OUT

IN

OUT

IN

≅

[(

–

12

used for design because even significant deviations do not

offer much relief. Note that the capacitor manufacturer’s

ripple current ratings are often based on 2000 hours of life.

This makes it advisable to further derate the capacitor, or

choose a capacitor rated at a higher temperature than

required. Always consult the manufacturer if there is any

question.

series resistance (ESR). Typically, once the ESR require-

∆≅ ∆

+









V

I ESR

fC

OUT

L

OUT

1

8

voltage, the output ripple is highest at maximum input

Aluminum electrolytic and dry tantalum capacitors are

both available in surface mount configurations. In the case

of tantalum, it is critical that the capacitors are surge tested

for use in switching power supplies. An excellent choice is

the AVX TPS series of surface mount tantalum. These are

specially constructed and tested for low ESR so they give

the lowest ESR for a given volume. Other capacitor types

include Sanyo POSCAP, Kemet T510 and T495 series, and

Sprague 593D and 595D series. Consult the manufacturer

for other specific recommendations.

which the output voltage is expected to slew quickly

according to the needs of the power amplifier. Holding the

output capacitor to 4.7

µF facilitates rapid charging and

discharging. When the output voltage descends quickly in

forced continuous mode, the LTC3403 will actually pull

satisfied. On alternate half cyles, this current actually exits

forcing current into the battery. To prevent deterioration

of the battery, use sufficient bulk capacitance with low

ESR; at least 10

µF is recommended.

APPLICATIO S I FOR ATIO