LTC3604 Datasheet, PDF (19/24 Pages) Linear Technology – 2.5A, 15V Monolithic Synchronous Step-Down Regulator

LTC3604
APPLICATIONS INFORMATION
Design Example
As a design example, consider using the LTC3604 in an
application with the following specifications:
V_IN = 12V, V_OUT = 1.8V, I_OUT(MAX) = 2.5A, 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 (ΔI_L(MAX) = 1A) using:
L
=
⎛
⎝⎜
1.8V ⎞
1MHz •1A⎠⎟
⎛
⎝⎜
1–
1.8V
12V
⎞
⎠⎟
=
1.53μH
C_IN should be sized for a maximum current rating of:
⎛ _{1.8V(12V – 1.8V)} ⎞
I_RMS
=
2.5A
⎜
⎝⎜
12V
⎟ _{= 0.89A}
⎠⎟
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.
A standard value 1.5μH 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 47μF ceramic
capacitor will be used.
V_IN
12V
C_IN
22μF
2.2μF
V_IN
BOOST
RUN
MODE/SYNC
SW
INTV_CC
V_ON
100k
LTC3604
FB
PGOOD
ITH
TRACK/SS
RT
324k _{SGND PGND}
3604 F08
C1
0.1μF L1
1.5μH
R3
C_F
80k
22pF
R4
40k
C_IN: TDK C3225X5R1C226M
C_OUT: TDK C3225X5R0J476M
L1: VISHAY IHLP2525CZER1R5M01
Figure 8. 1.8V, 2.5A Regulator at 1MHz
V_OUT
1.8V
C_OUT 2.5A
47μF
3604f
19