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

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LTC1778EGN-1

Wide Operating Range, No RSENSE™ Step-Down Controller

Linear Technology 

LTC1778/LTC1778-1

Wide Operating Range,

No RSENSETM Step-Down Controller

FEATURES

■ No Sense Resistor Required

■ True Current Mode Control

■ Optimized for High Step-Down Ratios

■ tON(MIN) ≤ 100ns

■ Extremely Fast Transient Response

■ Stable with Ceramic COUT

■ Dual N-Channel MOSFET Synchronous Drive

■ Power Good Output Voltage Monitor (LTC1778)

■ Adjustable On-Time (LTC1778-1)

■ Wide VIN Range: 4V to 36V

■ ±1% 0.8V Voltage Reference

■ Adjustable Current Limit

■ Adjustable Switching Frequency

■ Programmable Soft-Start

■ Output Overvoltage Protection

■ Optional Short-Circuit Shutdown Timer

■ Micropower Shutdown: IQ < 30µA

■ Available in a 16-Pin Narrow SSOP Package

U

APPLICATIO S

■ Notebook and Palmtop Computers

■ 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.

All other trademarks are the property of their respective owners.

Protected by U.S. Patents, including 5481178, 6100678, 6580258, 5847554, 6304066

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

1778fb

1

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