12

LTC1707

OUTPUT CURRENT (mA)

1

100

1000

1707 F08b

10

100

90

80

70

60

50

L = 15

µH

Burst Mode OPERATION

0.1

µF

†

100

µF

6.3V

††

22

µF

16V

22

µH*

* SUMIDA CD54-220

R2

169k

1%

R1

80.6k

1%

47pF

1

2

3

4

8

7

6

5

SYNC/MODE

SW

RUN/SS

GND

LTC1707

2.85V TO

4.5V

2.5V

0.3A

1707 F08a

+

+

Figure 8. Single Lithium-Ion to 2.5V/0.3A Regulator from Design Example

Design Example

As a design example, assume the LTC1707 is used in a

single lithium-ion battery-powered cellular phone applica-

down to about 2.85V. The load current requirement is a

maximum of 0.3A 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 2.5V. With

this information we can calculate L using equation (1),

L

fI

V

V

V

L

OUT

OUT

IN

−









1

1

∆

(3)

f = 350kHz in equation (3) gives:

L

V

kHz

mA

V

V

H

)

−









=

25

350

120

1

25

42

24 1

..

.

.

µ

A 22

µH inductor works well for this application. For best

efficiency choose a 1A inductor with less than 0.25

Ω

series resistance.

0.25

Ω. In most applications, the requirements for these

capacitors are fairly similar.

For the feedback resistors, choose R1 = 80.6k. R2 can then

be calculated from equation (2) to be:

R

V

Rk

OUT

2

08

1

1 171

=−









=

.

; use 169k

Figure 8 shows the complete circuit along with its effi-

ciency curve.

APPLICATIO S I FOR ATIO