Datasheet

LTC3605
16
3605fc
OPERATION
Design Example
As a design example, consider using the LTC3605 in an
application with the following specifications:
V
IN
= 10.8V to 13.2V, V
OUT
= 1.8V, I
OUT(MAX)
= 5A,
I
OUT(MIN)
= 500mA, f = 2MHz
Because efficiency is important at both high and low load
current, discontinuous mode operation will be utilized.
First select from the characteristic curves the correct R
T
resistor value for 2MHz switching frequency. Based on that
R
T
should be 80.6k. Then calculate the inductor value for
about 50% ripple current at maximum V
IN
:
L =
1.8V
2MHz• 2.5A






1–
1.8V
13.2V






= 0.31µH
The nearest standard value inductor would be 0.33µH.
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, two
47µF ceramic capacitors will be used.
C
IN
should be sized for a maximum current rating of:
I
RMS
= 5A
1.8V
13.2V






13.2V
1.8V
– 1






1/2
= 1.7A
Decoupling the PV
IN
pins with two 22µF ceramic capacitors
is adequate for most applications.