Datasheet

LTC3600
17
3600fc
Design Example
As a design example, consider using the LTC3600 in an
application with the following specifications:
V
IN
= 10.8V to 13.2V
V
OUT
= 1.8V
I
OUT(MAX)
= 1.5A
I
OUT(MIN)
= 500mA
f
SW
= 2MHz
First, R
SET
is selected based on:
R
SET
=
V
OUT
50µA
=
1.8V
50µA
= 36kΩ
For best accuracy, a 0.1% 36.1k resistor is selected.
Because efficiency is important at both high and low load
current, discontinuous mode operation will be utilized.
Select from the characteristic curves the correct R
T
resis-
tor value for 2MHz switching frequency. Based on that,
R
T
should be 18.2k. Then calculate the inductor value for
about 40% ripple current at maximum V
IN
:
L = =
1.8V
2MHz
• 0.6A






1−
1.8V
13.2V






1.3µH
The nearest standard value inductor would be 1.2µH.
C
OUT
will be selected based on the ESR that is required to
satisfy the output voltage ripple requirement and the bulk
capacitance needed for loop stability. For this design, one
47µF ceramic capacitor will be used.
C
IN
should be sized for a maximum current rating of:
I
RMS
= 1.5A
1.8V
13.2V






13.2V
1.8V
− 1






1/2
= 0.51A
Decoupling the V
IN
pin with one 22µF ceramic capacitor
is adequate for most applications.
applicaTions inForMaTion