LTC1700EMS 查看數據表（PDF） - Linear Technology

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LTC1700EMS

No RSENSE Synchronous Step-Up DC/DC Controller

Linear Technology 

LTC1700

W

FUNCTIONAL DIAGRA

SYNC/

MODE

5

ITH 2

BURST

INHIBIT

X

Y Y = “0” ONLY WHEN X IS A CONSTANT “1”, OTHERWISE Y = “1”

SLOPE

COMP

MAIN

OSC

–

90% DUTY

CYCLE LIMIT

VFB 3

–

EA

1.205V +

gm = 0.9m

VOUT 7

RUN/SS 4

SGND 1

1.205V

REFERENCE

SC

+

RUN/

SOFT-START

0.12V

VOUT

–

BURST

+

3.8µA

VREF + 58mV

VFB

SLEEP

–

OV

+

VCC

0.36V

VOUT

SWITCHING

LOGIC

AND

BLANKING

CIRCUIT

VOUT

6 TG

8 BG

9 PGND

= “1” WHEN VOUT < 2.3V

START-UP

OSCILLATOR

S QB

L1

RQ

SHDN

ICMP

SW 10

VOUT

9mV

+

IRCMP

–

M1

+

VDS

–

1Ω

60mV

1700 • FD

U

OPERATIO (Refer to Functional Diagram)

Main Control Loop

The LTC1700 is a constant frequency, current mode

controller for DC/DC step-up converters. In normal opera-

tion, the main external N-channel power MOSFET is turned

on when the oscillator sets a latch and turned off either

when the VDS sense amplifier (VDS) resets the latch or the

duty cycle has reached 90%. When the main MOSFET is

turned off, the synchronous rectifier P-channel MOSFET is

6

turned on until either the inductor current is about to

reverse, as determined by the current reversal comparator

(IRCMP), or the next cycle begins. Inductor current is

measured by sensing the VDS potential across the con-

ducting MOSFET. The peak inductor current is controlled

by the voltage on the ITH pin, which is the output of the

error amplifier (EA). An external resistive divider con-

nected between VOUT and GND allows EA to receive an

1700fa

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