LTC3544B

13

3544bfa

APPLICATIONS INFORMATION

Design Example

As a design example, consider using the LTC3544B as

a portable application with a Li-Ion battery. The battery

2.5V is 250mA necessitating the use of the 300mA output

for this requirement.

Beginning with this channel, first calculate the inductor

value for about 35% ripple current (100mA in this example)

L

V

MHz

mA

V

V

µH

4

25

2 25

100

1

25

42

45

=

⎛

⎝⎜

⎞

⎠⎟

=

.

.•

–

.

.

.

For the inductor, use the closest standard value of 4.7μH.

A 4.7μF capacitor should be sufficient for the output ca-

pacitor. A larger output capacitor will attenuate the load

transient response, but increase the settling time. A value

a Li-Ion battery is very low.

The feedback resistors program the output voltage.

Minimizing the current in these resistors will maximize

efficiency at very light loads, but totals on the order of

200k are a good compromise between efficiency and im-

munity to any adverse effects of PCB parasitic capacitance

on the feedback pins. Choosing 10μA with 0.8V feedback

voltage makes R7 = 80k. A close standard 1% resistor is

76.8k. Using:

R

V

Rk

OUT

8

08

1

7

163 2

= ⎛

⎝⎜

⎞

⎠⎟

=

.

–•

.

The closest standard 1% resistor is 162k. An optional

20pF feedback capacitor may be used to improve transient

response. The component values for the other channels

are chosen in a similar fashion.

Figure 5 shows the complete schematic for this example,

along with the efficiency curve and transient response for

the 300mA channel.

Figure 4

C1

C9

C10

GND

L1

L4

L2

L3

PGND

3544B F04

C4

C3

C2