LTC3631 Datasheet, PDF (9/22 Pages) Linear Technology – High Effi ciency, High Voltage 100mA Synchronous Step-Down Converter

LTC3631
OPERATION (Refer to Block Diagram)
then the output voltage will be limited by the ramp rate
on the SS pin instead. The internal and external soft-start
functions are reset on start-up and after an undervoltage
or overvoltage event on the input supply.
In order to ensure a smooth start-up transition in any
application, the internal soft-start also ramps the peak
inductor current from 50mA during its 1ms ramp time to
the set peak current threshold. The external ramp on the
SS pin does not limit the peak inductor current during
start-up; however, placing a capacitor from the I_SET pin
to ground does provide this capability.
Peak Inductor Current Programming
The offset of the peak current comparator nominally
provides a peak inductor current of 225mA. This peak
inductor current can be adjusted by placing a resistor
from the I_SET pin to ground. The 1μA current sourced out
of this pin through the resistor generates a voltage that is
translated into an offset in the peak current comparator,
which limits the peak inductor current.
Input Undervoltage and Overvoltage Lockout
The LTC3631 implements a protection feature which dis-
ables switching when the input voltage is not within the
4.5V to 45V operating range. If V_IN falls below 4V typical
(4.35V maximum), an undervoltage detector disables
switching. Similarly, if V_IN rises above 50V typical (47V
minimum), an overvoltage detector disables switching.
When switching is disabled, the LTC3631 can safely sustain
input voltages up to the absolute maximum rating of 60V.
Switching is enabled when the input voltage returns to the
4.5V to 45V operating range.
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