LTC3778 查看數據表（PDF） - Linear Technology

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LTC3778

Wide Operating Range, No RSENSE™ Step-Down Controller

Linear Technology 

FEATURES

s Wide VIN Range: 4V to 36V

s Sense Resistor Optional

s True Current Mode Control

s 2% to 90% Duty Cycle at 200kHz

s tON(MIN) ≤ 100ns

s Stable with Ceramic COUT

s Dual N-Channel MOSFET Synchronous Drive

s Power Good Output Voltage Monitor

s ±1% 0.6V Reference

s Adjustable Current Limit

s Adjustable Switching Frequency

s Programmable Soft-Start

s Output Overvoltage Protection

s Optional Short-Circuit Shutdown Timer

s Micropower Shutdown: IQ ≤ 30µA

s Available in a 1mm 20-Lead TSSOP Package

U

APPLICATIO S

s Notebook and Palmtop Computers, PDAs

s Battery Chargers

s Distributed Power Systems

s DDR Memory Power Supply

s Automobile DC Power Supply

LTC3778

Wide Operating Range,

No RSENSETM Step-Down Controller

DESCRIPTIO

The LTC®3778 is a synchronous step-down switching

regulator controller for computer memory, automobile

and other DC/DC power supplies. The controller uses a

valley current control architecture to deliver very low duty

cycles without requiring a sense resistor. Operating fre-

quency is selected by an external resistor and is compen-

sated for variations in VIN and VOUT.

Discontinuous mode operation provides high efficiency

operation at light loads. A forced continuous control pin

reduces noise and RF interference, and can assist second-

ary winding regulation when the main output is lightly

loaded. SENSE+ and SENSE– pins provide true Kelvin

sensing across the optional sense resistor or the

sychronous MOSFET.

Fault protection is provided by internal foldback current

limiting, an output overvoltage comparator, optional short-

circuit shutdown timer and input undervoltage lockout.

Soft-start capability for supply sequencing is accom-

plished using an external timing capacitor. The regulator

current limit level is user programmable. Wide supply

range allows operation from 4V to 36V at the input and

from 0.6V up to (0.9)VIN at the output.

, LTC and LT are registered trademarks of Linear Technology Corporation.

No RSENSE is a trademark of Linear Technology Corporation.

TYPICAL APPLICATIO

CC

500pF

CSS

0.1µF

RC

20k

ION

VIN

RUN/SS TG

SW

ITH

BOOST

LTC3778

SGND

INTVCC

DRVCC

BG

SENSE+

SENSE–

PGOOD PGND

RON

1.4M

CB 0.22µF

DB

CMDSH-3

+ CVCC

4.7µF

M1

Si4884 L1

1.8µH

M2

Si4874

D1

B340A

VFB

VIN

CIN 5V TO 28V

10µF

35V

×3 VOUT

2.5V

+ COUT 10A

180µF

4V

×2

R2

40.2k

R1

12.7k

3778 F01a

Figure 1. High Efficiency Step-Down Converter

Efficiency vs Load Current

100

VIN = 5V

90

VIN = 25V

80

70

60

0.01

0.1

1

LOAD CURRENT (A)

10

3778 F01b

3778f

1

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