LT3580EDD-TRPBF Ver la hoja de datos (PDF) - Linear Technology

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LT3580EDD-TRPBF

Boost/Inverting DC/DC Converter with 2A Switch, Soft-Start, and Synchronization

Linear Technology 

LT3580

BLOCK DIAGRAM

RC

CSS

CC

VIN

CIN

SHDN

7

SS

2

VC

5

–

1.3V +

DISCHARGE

DETECT

L1

UVLO

VIN

3

1.215V

REFERENCE

SR2

R

Q

S

275k

SOFT-

START

Q2

VC

ILIMIT

SW

D1

4

COMPARATOR

–

SR1

DRIVER

C1

A3

R

Q

Q1

+

S

+

14.6k

A1

∑

A4

0.01Ω

–

FB

1

+

14.6k

A2

RAMP

GENERATOR

FREQUENCY ÷N ADJUSTABLE

FOLDBACK

OSCILLATOR

GND

9

–

SYNC

BLOCK

SYNC

8

RT

6

RT

VOUT

RFB

3580 BD

OPERATION

The LT3580 uses a constant-frequency, current mode con-

trol scheme to provide excellent line and load regulation.

Refer to the Block Diagram which shows the LT3580 in a

boost configuration. At the start of each oscillator cycle,

the SR latch (SR1) is set, which turns on the power switch,

Q1. The switch current flows through the internal current

sense resistor generating a voltage proportional to the

switch current. This voltage (amplified by A4) is added

to a stabilizing ramp and the resulting sum is fed into the

positive terminal of the PWM comparator A3. When this

voltage exceeds the level at the negative input of A3, the SR

latch is reset, turning off the power switch. The level at the

negative input of A3 (VC pin) is set by the error amplifier A1

(or A2) and is simply an amplified version of the difference

between the feedback voltage (FB pin) and the reference

voltage (1.215V or 5mV depending on the configuration).

In this manner, the error amplifier sets the correct peak

current level to keep the output in regulation.

The LT3580 has a novel FB pin architecture that can be

used for either boost or inverting configurations. When

configured as a boost converter, the FB pin is pulled up

to the internal bias voltage of 1.215V by the RFB resistor

connected from VOUT to FB. Comparator A2 becomes

inactive and comparator A1 performs the inverting

amplification from FB to VC. When the LT3580 is in an

inverting configuration, the FB pin is pulled down to 5mV

by the RFB resistor connected from VOUT to FB. Comparator

A1 becomes inactive and comparator A2 performs the

noninverting amplification from FB to VC.

3580fg

6

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