LTC3601_15 Datasheet, PDF (20/26 Pages) Linear Technology – 1.5A, 15V Monolithic Synchronous Step-Down Regulator

LTC3601
APPLICATIONS INFORMATION
Design Example
As a design example, consider using the LTC3601 in an
application with the following specifications:
V_IN = 12V, V_OUT = 1.8V, I_OUT(MAX) = 1.5A, I_OUT(MIN) =
10mA, f = 1MHz
Because efficiency 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
=




1MHz1•.86V00mA ^{
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.
V_IN
4V TO 15V
C_IN
22μF
2.2μF
V_IN
BOOST
RUN
MODE/SYNC
SW
INTV_CC
V_ON
LTC3601
100k
FB
PGOOD
ITH
TRACK
RT
324k _SGND
PGND
3601 F05
C1
0.1μF L1
2.2μH
R3
C_FWD
80k
10pF
R4
40k
C_IN: TDK C3225X5R1C226M
C_OUT: TDK C3225X5R0J476M
L1: VISHAY IHLP2020BZER2R2M01
Figure 7. 1.8V, 1.5A Regulator at 1MHz
V_OUT
1.8V
C_OUT 1.5A
47μF
3601fb
20