LTC3788 Datasheet, PDF (27/32 Pages) Linear Technology – 2-Phase, Dual Output Synchronous Boost Controller

LTC3788
APPLICATIONS INFORMATION
Reduce V_IN from its nominal level to verify operation with
high duty cycle. Check the operation of the undervoltage
lockout circuit by further lowering V_IN while monitoring
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
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.
SENSE1^–
SENSE1⁺
ILIM
PGOOD1
SS1
SW1
TG1
LTC3788
BOOST1
ITH1
BG1
VFB1
VBIAS
FREQ
PHSMD
PGND
CLKOUT
EXTV_CC
f_IN
PLLIN/MODE INTV_CC
SGND
RUN1
RUN2
BG2
VFB2
BOOST2
ITH2
TG2
SW2
SS2
SENSE2⁺
SENSE2^–
PGOOD2
V_PULL-UP
C_B1
C_B2
V_PULL-UP
L1 ^RSENSE1
M1
+
M2
V_OUT1
GND
V_IN
M3
+
M4
L2 ^RSENSE2
V_OUT2
3788 F07
Figure 7. Recommended Printed Circuit Layout Diagram
3788f
27