LTC3832 datasheet(7/24 Pages) LINER

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LTC3832/LTC3832-1

sn3832 3832fs

PI FU CTIO S

FREQSET (Pin 11/NA): Frequency Set. Use this pin to

adjust the free-running frequency of the internal oscillator.

With the pin floating, the oscillator runs at about 300kHz.

A resistor from FREQSET to ground speeds up the oscil-

lator; a resistor to VCC slows it down.

IMAX (Pin 12/NA): Current Limit Threshold Set. IMAX sets

the threshold for the internal current limit comparator. If

IFB drops below IMAX with G1 on, the LTC3832 goes into

current limit. IMAX has an internal 12µA pull-down to GND.

Connect this pin to the main VIN supply at the drain of Q1,

through an external resistor to set the current limit thresh-

old. Connect a 0.1

µF decoupling capacitor across this

resistor to filter switching noise.

IFB (Pin 13/NA): Current Limit Sense. Connect this pin to

the switching node at the source of Q1 and the drain of Q2

through a 1k resistor. The 1k resistor is required to prevent

voltage transients from damaging IFB.This pin is used for

sensing the voltage drop across the upper N-channel

MOSFET, Q1.

VCC (Pin 14/Pin 7): Power Supply Input. All low power

internal circuits draw their supply from this pin. Connect

this pin to a clean power supply, separate from the main

VIN supply at the drain of Q1. This pin requires a 4.7µF

bypass capacitor. The LTC3832-1has VCC and PVCC2 tied

together at Pin 7 and requires a 10

µF bypass capacitor to

GND.

PVCC2 (Pin 15/Pin 7): Power Supply Input for G2. Connect

this pin to the main high power supply.

G2 (Pin 16/Pin 8): Bottom Gate Driver Output. Connect

this pin to the gate of the lower N-channel MOSFET, Q2.

This output swings from PGND to PVCC2. It remains low

when G1 is high or during shutdown mode. To prevent

output undershoot during a soft-start cycle, G2 is held low

until G1 first goes high (FFBG in the Block Diagram).

BLOCK DIAGRA

–

PVCC1

PVCC2

PGND

SENSE+

VREF

VREF + 10%

18k

5.7k

SENSE–

3832 BD

POR

FFBG

ENABLE

PWM

QSS

VREF

VREF + 10%

MAX

ERR

µA

INTERNAL

OSCILLATOR

100

µs DELAY

SHDN

FREQSET

COMP

POWER DOWN

DISABLE GATE DRIVE

LOGIC AND

THERMAL SHUTDOWN

–

2.2V

1.2V

PVCC1

VCC + 2.5V

µA

DISABLE

ILIM

IMAX

IFB

VCC

GND

–

(LTC3832)

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