Datasheet

LTC3642
9
3642fc
OPERATION
(Refer to Block Diagram)
inductor current from 25mA 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 115mA. 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 LTC3642 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 LTC3642 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.