Datasheet

LTC3827
27
3827ff
APPLICATIONS INFORMATION
C
IN
is chosen for an RMS current rating of at least 3A at
temperature assuming only this channel is on. C
OUT
is
chosen with an ESR of 0.02 for low output ripple. The
output ripple in continuous mode will be highest at the
maximum input voltage. The output voltage ripple due to
ESR is approximately:
V
ORIPPLE
= R
ESR
(ΔI
L
) = 0.02(1.67A) = 33mV
P-P
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the IC. These items are also illustrated graphically in the
layout diagram of Figure 11. Figure 12 illustrates the current
waveforms present in the various branches of the 2-phase
synchronous regulators operating in the continuous mode.
Check the following in your layout:
1. Are the top N-channel MOSFETs M1 and M3 located
within 1cm of each other with a common drain connec-
tion at C
IN
? Do not attempt to split the input decoupling
for the two channels as it can cause a large resonant
loop.
Figure 11. Recommended Printed Circuit Layout Diagram
C
B2
C
B1
R
PU1
PGOOD1
V
PULL-UP
(<8.5V)
C
INTVCC
+
C
IN
D1
1µF
CERAMIC
M1 M2
M3
M4
D2
C
VIN
V
IN
R
IN
L1
L2
C
OUT1
V
OUT1
GND
V
OUT2
3827 F11
C
OUT2
R
SENSE
R
SENSE
R
PU2
PGOOD2
V
PULL-UP
(<8.5V)
f
IN
1µF
CERAMIC
I
TH1
V
FB1
SENSE1
+
SENSE1
–
PLLLPF
SENSE2
–
SENSE2
+
V
FB2
I
TH2
TRACK/SS2
TRACK/SS1
PGOOD2
PGOOD1
TG1
SW1
BOOST1
BG1
V
IN
PGND
EXTV
CC
INTV
CC
BG2
BOOST2
SW2
TG2
FOLDIS
PHASMD
CLKOUT
PLLIN/MODE
RUN1
RUN2
SGND
+
+
+