LT1616 데이터 시트보기 (PDF) - Linear Technology

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LT1616

600mA, 1.4MHz Step-Down Switching Regulator in SOT-23

Linear Technology 

BLOCK DIAGRA

VIN 5

SHDN 4

INT REG

AND

UVLO

Σ

SLOPE

COMP

OSC

FREQUENCY

FOLDBACK

VC

RQ

SQ

gm

1.25V

LT1616

1 BOOST

DRIVER

Q1

6 SW

2

GND

3

1616BD

FB

U

OPERATIO (Refer to Block Diagram)

The LT1616 is a constant frequency, current mode Buck

regulator. The 1.4MHz oscillator enables an RS flip-flop,

turning on the internal 600mA power switch Q1. An ampli-

fier and comparator monitor the current flowing between

the VIN and SW pins, turning the switch off when this current

reaches a level determined by the voltage at VC. An error

amplifier measures the output voltage through an external

resistor divider tied to the FB pin. This amplifier servos the

switch current to regulate the FB pin voltage to 1.25V. An

active clamp on the VC node provides current limit.

An internal regulator provides power to the control cir-

cuitry. This regulator includes an undervoltage lockout to

prevent switching when VIN is less than ~ 3.5V. The

SHDN pin is used to place the LT1616 in shutdown,

disconnecting the output and reducing the input current

to less than 1µA.

The switch driver operates from either the input or from

the BOOST pin. An external capacitor and diode are used

to generate a voltage at the BOOST pin that is higher than

the input supply. This allows the driver to fully saturate the

internal bipolar NPN power switch for efficient operation.

The oscillator reduces the LT1616’s operating frequency

when the voltage at the FB pin is low. This frequency

foldback helps to control the output current during start-

up and overload.

5

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