LT1940 Ver la hoja de datos (PDF) - Linear Technology

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Fabricante

LT1940

Dual Monolithic 1.4A, 1.1MHz Step-Down Switching Regulator

Linear Technology 

LT1940/LT1940L

BLOCK DIAGRA

2µA

RUN/SS2

2µA

RUN/SS1

VIN

INT REG

AND REF

MASTER

OSC

CLK1

CLK2

0.75V

∑

SLOPE

R

SQ

C1

SLAVE

CLK

OSC

0.5V

VC

RC

CF

CC RUN/SS

PG

GND

–

+

ILIMIT

CLAMP

ERROR

AMP

VIN

IN

CIN

BOOST

D2

C3

SW

L1

OUT

D1

C1

FB

R1

R2

1.25V

125mV

1940 F02

Figure 2. Block Diagram of the LT1940 with Associated External Components (One of Two Switching Regulators Shown)

The LT1940 is a dual, constant frequency, current mode

buck regulator with internal 2A power switches. The two

regulators share common circuitry including input source,

voltage reference and oscillator, but are otherwise inde-

pendent. This section describes the operation of the

LT1940; refer to the Block Diagram.

If the RUN/SS (run/soft-start) pins are both tied to ground,

the LT1940 is shut down and draws 30µA from the input

source tied to VIN. Internal 2µA current sources charge

external soft-start capacitors, generating voltage ramps at

6

these pins. If either RUN/SS pin exceeds 0.6V, the internal

bias circuits turn on, including the internal regulator,

1.25V reference and 1.1MHz master oscillator. In this

state, the LT1940 draws 3.5mA from VIN, whether one or

both RUN/SS pins are high. Neither switching regulator

will begin to operate until its RUN/SS pin reaches ~0.8V.

The master oscillator generates two clock signals of

opposite phase.

The two switchers are current mode step-down regula-

tors. This means that instead of directly modulating the

1940fa

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