LT1767EMS8E-1.8-TRPBF Просмотр технического описания (PDF) - Linear Technology

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Компоненты Описание

производитель

LT1767EMS8E-1.8-TRPBF

Monolithic 1.5A, 1.25MHz Step-Down Switching Regulators

Linear Technology 

LT1767/LT1767-1.8/

LT1767-2.5/LT1767-3.3/LT1767-5

APPLICATIONS INFORMATION

VIN

12V C3

2.2µF

CERAMIC

D2

CMDSH-3

OPEN

OR

HIGH

= ON

C2

0.1µF

BOOST

VIN

VSW

LT1767-2.5

SHDN

FB

SYNC GND VC

CC

1.5nF

RC

4.7k

L1

5µH

D1

UPS120

OUTPUT

2.5V

1.2A

C1

10µF

CERAMIC

1767 F06a

C3

VIN

MINIMIZE LT1767,

C3, D1 LOOP

D2

C2

GND

PLACE FEEDTHROUGHS

AROUND GROUND PIN

AND UNDER GROUND PAD

FOR GOOD THERMAL

CONDUCTIVITY

SYNC

SHDN

KEEP FB AND VC

COMPONENTS

AWAY FROM

HIGH INPUT

COMPONENTS

D1

CC

L1

RC

VOUT

C1 GND

CONNECT TO

GROUND PLANE

KELVIN SENSE

VOUT

1767 F06

Figure 6. Typical Application and Suggested Layout (Topside Only Shown)

THERMAL CALCULATIONS

Power dissipation in the LT1767 chip comes from four

sources: switch DC loss, switch AC loss, boost circuit

current, and input quiescent current. The following

formulas show how to calculate each of these losses.

These formulas assume continuous mode operation, so

they should not be used for calculating efficiency at light

load currents.

Switch loss:

PSW

= RSW

(IOUT )2

VIN

(VOUT )

+ 17ns

(IOUT) (VIN) (f)

Boost current loss for VBOOST = VOUT:

( ) PBOOST

=

VOUT 2

IOUT

VIN

/ 50

Quiescent current loss:

PQ =VIN (0.001)

RSW = Switch resistance (≈ 0.27Ω when hot)

17ns = Equivalent switch current/voltage overlap time

f = Switch frequency

1767fb

For more information www.linear.com/LT1767

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