LTC3633A Datasheet, PDF (22/28 Pages) Linear Technology – Dual Channel 3A, 20V Monolithic Synchronous Step-Down Regulator

LTC3633A/LTC3633A-1
APPLICATIONS INFORMATION
A 47μF ceramic capacitor should be sufficient for channel 1.
Solving the same equation for channel 2 (using 5% of
V_OUT for V_DROOP) results in 27μF of capacitance (22μF is
the closest standard value).
C_IN should be sized for a maximum current rating of:
I_RMS = 3A
1.8V₍13.2V − 1.8V_{) = 1A}
13.2V
Solving this equation for channel 2 results in an RMS
input current of 1.3A. Decoupling each V_IN input with
a 47μF ceramic capacitor should be adequate for most
applications.
Lastly, the feedback resistors must be chosen. Picking R1
and R3 to be 12.1k, R2 and R4 are calculated to be:
R2
=
(12.1k)
•
⎛ _1.8V
⎝⎜ 0.6V
– 1^{⎞⎠⎟}=
24.2k
R4
=
(12.1k)
•
⎛ _3.3V
⎝⎜ 0.6V
– 1^{⎞⎠⎟}
=
54.5k
The final circuit is shown in Figure 8.
V_IN
12V
C_IN
47μF
×2
R5
162k
V_OUT2
3.3V AT 3A
C_OUT2
22μF
L2
1μH ^0.1μF
R4
R3
54.9k _12.1k
RUN1
RUN2
V_IN2 V_{IN1 INTVCC}
ITH1
LTC3633A
ITH2
V2P5
RT
TRACKSS2
PGOOD2
BOOST2
MODE/SYNC
PHMODE
TRACKSS1
PGOOD1
BOOST1
SW2
V_ON2
V_{FB2 SGND PGND}
SW1
V_ON1
V_FB1
CV_CC
2.2μF
L1
0.1μF _0.68μH
R1
R2
12.1k ^24.3k
Figure 8. Design Example Circuit
V_OUT1
1.8V AT 3A
C_OUT1
47μF
3633a F08
3633a1f
22