LTC3788 Linear Technology, LTC3788 Datasheet - Page 27

• Manufacturer Part Number: LTC3788
• Description: Dual Output Synchronous Boost Controller
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
Reduce V
high duty cycle. Check the operation of the undervoltage
lockout circuit by further lowering V
the outputs to verify operation.
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
IN
from its nominal level to verify operation with
f
IN
Figure 7. Recommended Printed Circuit Layout Diagram
IN
SENSE1
SENSE1
SS1
ITH1
VFB1
FREQ
PHSMD
CLKOUT
PLLIN/MODE
SGND
RUN1
RUN2
VFB2
ITH2
SS2
SENSE2
SENSE2
while monitoring
LTC3788
–
+
+
–
PGOOD2
PGOOD1
BOOST2
BOOST1
EXTV
INTV
VBIAS
PGND
SW2
ILIM
SW1
BG2
TG2
TG1
BG1
CC
CC
effects of differential noise injection due to high frequency
capacitive coupling.
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.
V
V
PULL-UP
PULL-UP
C
C
B1
B2
M2
M3
GND
M1
M4
L1
L2
+
R
R
SENSE1
SENSE2
+
3788 F07
V
V
V
OUT1
IN
OUT2
LTC3788
27
3788f