LTC3632 datasheet(9/22 Pages) LINER

9 / 22 page

LTC3632

3632fb

OPERATION (Refer to Block Diagram)

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 10mA during its 0.75ms 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 ISET pin to

ground does provide this capability.

Peak Inductor Current Programming

The offset of the peak current comparator nominally pro-

vides a peak inductor current of 50mA. This peak inductor

current can be adjusted by placing a resistor from the ISET

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 LTC3632 implements a protection feature which dis-

ables switching when the input voltage is not within the

4.5V to 50V operating range. If VIN falls below 4V typical

(4.35V maximum), an undervoltage detector disables

switching. Similarly, if VIN rises above 55V typical (53V

minimum), an overvoltage detector disables switching.

When switching is disabled, the LTC3632 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 50V operating range.

LTC3632 Arkusz danych(PDF) 9 Page - Linear Technology