LTC3602 datasheet(10/36 Pages) LINER

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LTC3613

3613fa

FUNCTIONAL DIAGRAM

ICMP

(gm(EA) = 1.7mS)

0.645V

0.555V

0.6V

1μA

IREV

LOGIC

CONTROL

PLL

SYSTEM

ONE-SHOT

TIMER

CLOCK

DETECT

OSCILLATOR

LDO

OUT

SVIN

4.2V

TIME

ADJUST

STOP

START

1.2V

0.75V

–

(A = 1)

RPGD

PGOOD

MODE/PLLIN

VRNG

ITH

VOSNS

–

VOSNS

TRACK/SS

SENSE–

SENSE+

PGND

EXTVCC

BO0ST

INPUT SUPPLY

COUT

RFB2

RFB1

RSENSE

PVIN

INTVCC

SGND

RITH

CITH1

INTVCC

3.65V

UVLO

4.6V

VOUT

RUN

1.3μA

CVCC

VIN

CIN

VOUT

CIN

CSS

3613 FD

–

TG DRV

BG DRV

CLOCK

OPERATION

Main Control Loop

The LTC3613 uses valley current mode control to regulate

the output voltage in a monolithic, all N-channel MOSFET

DC/DC step-down converter. Current control is achieved by

sensing the inductor current across SENSE+ and SENSE–,

either by using an explicit resistor connected in series with

the inductor or by implicitly sensing the inductor’s resis-

tive (DCR) voltage drop through an RC filter connected

across the inductor.

In normal steady-state operation, the top MOSFET is turned

on for a fixed time interval proportional to the delay in the

one-shot timer. The PLL system adjusts the delay in the

one-shot timer until the top MOSFET turn-on is synchro-

nized either to the internal oscillator or the external clock

input if provided. As the top MOSFET turns off, the bottom

MOSFET turns on with a small time delay (dead time) to

avoid shoot-through current. The next switching cycle is

initiated when the current comparator, ICMP, senses that

inductor current has reached the valley threshold point

(Refer to Functional Diagram)

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