LTC3633
22
3633fd
For more information www.linear.com/LTC3633
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
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.
Figure 8. Design Example Circuit
RUN1
RUN2
RT
TRACKSS2
PGOOD2
LTC3633
BOOST2
0.1µF
L2
1µH
R4
54.9k
R3
12.1k
SW2
V
ON2
V
IN2
V
IN1
V
FB2
PHMODE
TRACKSS1
PGOOD1
BOOST1
SW1
V
ON1
V
FB1
C
OUT2
22µF
V
OUT2
0.1µF
L1
0.68µH
R2
24.3k
R1
12.1k
C
OUT1
47µF
V
OUT1
IN
12V
C
IN
47µF
×2
R5
162k
MODE/SYNC
ITH1
ITH2
V2P5
INTV
CC
C2
2.2µF
PGNDSGND
