LTC1778EGN-1(RevA) 查看數據表（PDF） - Linear Technology

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LTC1778EGN-1
(Rev.:RevA)

Wide Operating Range, No RSENSE™ Step-Down Controller

Linear Technology 

LTC1778/LTC1778-1

Wide Operating Range,

No RSENSETM Step-Down Controller

FEATURES

s No Sense Resistor Required

s True Current Mode Control

s Optimized for High Step-Down Ratios

s tON(MIN) ≤ 100ns

s Extremely Fast Transient Response

s Stable with Ceramic COUT

s Dual N-Channel MOSFET Synchronous Drive

s Power Good Output Voltage Monitor (LTC1778)

s Adjustable On-Time (LTC1778-1)

s Wide VIN Range: 4V to 36V

s ±1% 0.8V Voltage 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 16-Pin Narrow SSOP Package

U

APPLICATIO S

s Notebook and Palmtop Computers

s Distributed Power Systems

DESCRIPTIO

The LTC®1778 is a synchronous step-down switching

regulator controller optimized for CPU power. The con-

troller uses a valley current control architecture to deliver

very low duty cycles with excellent transient response

without requiring a sense resistor. Operating frequency is

selected by an external resistor and is compensated for

variations in VIN.

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 by disabling discontinuous opera-

tion when the main output is lightly loaded.

Fault protection is provided by internal foldback current

limiting, an output overvoltage comparator and optional

short-circuit shutdown timer. Soft-start capability for sup-

ply sequencing is accomplished using an external timing

capacitor. The regulator current limit level is user program-

mable. Wide supply range allows operation from 4V to 36V

at the input and from 0.8V 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

CSS

0.1µF

CC

500pF

RC

20k

ION

VIN

RUN/SS TG

SW

ITH

BOOST

LTC1778

SGND INTVCC

BG

PGOOD PGND

RON

1.4MΩ

CB 0.22µF

DB

CMDSH-3

+ CVCC

4.7µF

M1

Si4884 L1

1.8µH

M2

Si4874

D1

B340A

CIN

10µF

VIN

5V TO 28V

50V

×3

VOUT

2.5V

+ COUT 10A

180µF

4V

×2

R2

30.1k

VFB

R1

14k

1778 F01a

Figure 1. High Efficiency Step-Down Converter

Efficiency vs Load Current

100

VOUT = 2.5V

VIN = 5V

90

VIN = 25V

80

70

60

0.01

0.1

1

LOAD CURRENT (A)

10

1778 F01b

1778fa

1

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