Datasheet

LTC3601
20
3601fb
Design Example
As a design example, consider using the LTC3601 in an
application with the following specifi cations:
V
IN
= 12V, V
OUT
= 1.8V, I
OUT(MAX)
= 1.5A, I
OUT(MIN)
=
10mA, f = 1MHz
Because effi ciency is important at both high and low load
currents, Burst Mode operation is selected.
First, the correct R
RT
resistor value for 1MHz switching
frequency must be chosen. Based on the equation dis-
cussed earlier, R
RT
should be 324k.
Next, determine the inductor value for approximately 40%
ripple current using:
L =
1.8V
1M H z • 6 0 0 m A






1–
1.8V
12V






= 2.55μH
A standard value 2.2µH inductor will work well for this
application.
Next, C
OUT
is selected based on the required output
transient performance and the required ESR to satisfy
the output voltage ripple. For this design, a 22µF ceramic
capacitor will be used.
C
IN
should be sized for a maximum current rating of:
I
RMS
= 1.5A
1.8V 12V – 1.8V
()
12V








= 0.54A
Decoupling the V
IN
pins with a 22µF ceramic capacitor
should be adequate for most applications. A 0.1µF boost
capacitor should also work for most applications.
To save board space the I
TH
pin is connected to the INTV
CC
pin to select an internal compensation network.
The PGOOD pin is connected to V
IN
through a 100k resistor.
Figure 7. 1.8V, 1.5A Regulator at 1MHz
APPLICATIONS INFORMATION
V
IN
MODE/SYNC
RUN
INTV
CC
PGOOD
ITH
RT
LTC3601
PGNDSGND
BOOST
SW
V
ON
FB
TRACK
2.2μF
C
FWD
10pF
C1
0.1μF
C
OUT
47μF
V
OUT
1.8V
1.5A
R3
80k
R4
40k
100k
324k
C
IN
: TDK C3225X5R1C226M
C
OUT
: TDK C3225X5R0J476M
L1: VISHAY IHLP2020BZER2R2M01
3601 F05
L1
2.2μH
C
IN
22μF
V
IN
4V TO 15V