LTC3409 datasheet(14/16 Pages) LINER

14 / 16 page

LTC3409

3409f

APPLICATIO S I FOR ATIO

Design Example

As a design example, assume the LTC3409 is used in a

2-alkaline cell battery-powered application. The VIN will be

operating from a maximum of 3.2V down to about 1.8V.

The load current requirement is a maximum of 600mA but

most of the time it will be in standby mode, requiring only

2mA. Efficiency at both low and high load currents is

important. Output voltage is 1.5V. With this information

we can calculate L using Equation 2:

OUT

∆

⎛

⎝

⎜

⎞

⎠

⎟

•

–

(2)

Substituting VOUT = 1.5V, VIN = 3.2V, ∆IL = 240mA and

f = 1.7MHz in Equation 2 gives:

MHz

⎛

⎝

⎜

⎞

⎠

⎟ ≅

1 7

240

15 1

.•

.–

For best efficiency choose a 750mA or greater inductor

with less than 0.3Ω series resistance. CIN will require an

RMS current rating of at least 0.3A ≅ ILOAD(MAX)/2 at

temperature.

For the feedback resistors, choose R2 = 133k. R1 can then

be calculated from Equation 2 at 191K. Figure 4 shows the

complete circuit along with its efficiency curve.

Table 2 below gives 1% resistor values for selected output

voltages.

VOUT

0.85V

51.1k

133k

1.2V

127k

133k

1.5V

191k

133k

1.8V

255k

133k

VFB

GND

VIN

SYNC

RUN

MODE

LTC3409

2.2µH

191k

10pF

CIN

4.7µF

VIN

1.6V TO 5.5V

133k

3409 F04

VOUT

1.5V

0.6A

COUT

10µF

CER

L1: SUMIDA CDRH2D18/LD

Figure 4

LOAD CURRENT (mA)

100

0.1

100

1000

3409 F04b

1.8VIN

3.2VIN

2.5VIN

Burst Mode Efficiency, 1.5VOUT

LTC3409 Datasheet(PDF) 14 Page - Linear Technology

LTC3409 Datasheet(HTML) 14 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Download

Link URL