LTC3858-1 Linear Technology Corporation, LTC3858-1 Datasheet - Page 29

• Manufacturer Part Number: LTC3858-1
• Description: Dual 2-Phase Synchronous Step-Down Controller
• Manufacturer: Linear Technology Corporation

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APPLICATIONS INFORMATION
to the phasing of the internal clocks and may cause minor
duty cycle jitter.
Reduce V
of the regulator in dropout. Check the operation of the
undervoltage lockout circuit by further lowering V
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. If problems are encountered with
IN
from its nominal level to verify operation
IN
while
high current output loading at lower input voltages, look
for inductive coupling between C
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 hookup 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.
IN
, Schottky and the top
LTC3858-1
29
38581f