Datasheet

LTC3788-1
24
37881fc
APPLICATIONS INFORMATION
Figure 7. Recommended Printed Circuit Layout Diagram
SENSE1
+
SENSE1
–
SENSE2
+
SENSE2
–
VFB1
ITH1
SGND
EXTV
CC
RUN1
RUN2
FREQ
SS2
VFB2
SS1
PLLIN/MODE
PGOOD1
TG1
SW1
BOOST1
BG1
VBIAS
INTV
CC
PGND
BG2
TG2
BOOST2
SW2
C
B1
C
B2
V
IN
V
OUT1
V
OUT2
LTC3788-1
L2
L1
M2
M3
37881 F07
V
PULL-UP
R
SENSE1
R
SENSE2
M1
M4
GND
ITH2
+
+
+
f
IN
Investigate whether any problems exist only at higher out-
put currents or only at higher input voltages. If problems
coincide with high input voltages and low output currents,
look for capacitive coupling between the BOOST, SW, TG,
and possibly BG connections and the sensitive voltage
and current pins. The capacitor placed across the current
sensing pins needs to be placed immediately adjacent to
the pins of the IC. This capacitor helps to minimize the
effects of differential noise injection due to high frequency
capacitive coupling. If problems are encountered with
high current output loading at lower input voltages, look
for inductive coupling between C
IN
, Schottky and the top
MOSFET components to the sensitive current and voltage
sensing traces. In addition, investigate common ground
path voltage pickup between these components and the
SGND pin of the IC.
An embarrassing problem, which can be missed in an
otherwise properly working switching regulator results
when the current sensing leads are hooked up backwards.
The output voltage under this improper hook-up will still
be maintained, but the advantages of current mode control
will not be realized. Compensation of the voltage loop will
be much more sensitive to component selection. This
behavior can be investigated by temporarily shorting out
the current sensing resistor—don’t worry, the regulator
will still maintain control of the output voltage.