LT1612EMS8 Просмотр технического описания (PDF) - Linear Technology

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LT1612EMS8

Synchronous, Step-Down 800kHz PWM DC/DC Converter

Linear Technology 

LT1612

PIN FUNCTIONS

VC (Pin 1): Compensation Pin. This is the current sink/

source output of the error amplifier. By connecting an RC

network from this pin to ground, frequency response can

be tuned for a wide range of circuit configurations. The

voltage at this pin also sets the current limit, and if

grounded, the switch will remain in the OFF state.

FB (Pin 2): Feedback Pin. This pin is the negative input to

the error amplifier. Connect the resistor divider tap to this

point which sets VOUT according to:

VOUT = 0.62V (1 + R1/R2)

VIN (Pin 3): Supply Pin. Bypass capacitor C1 must be right

next to this pin.

GND (Pin 4): Ground Pin. Connect directly to local ground

plane.

SW (Pin 5): Switch Pin. Connect inductor and boost

capacitor here. Minimize trace area at this pin to keep EMI

down.

BOOST (Pin 6): This is the supply pin for the switch driver

and must be above VIN by 1.5V for proper switch opera-

tion. Connect the boost capacitor to this pin.

MODE (Pin 7): Burst Mode Operation Disable Pin. For

continuous switching operation (low noise), pull this pin

above 2V. For Burst Mode operation which gives better

light load efficiency, tie to ground. Output ripple voltage in

Burst Mode operation is typically 30mVP-P. See applica-

tions section for more information about this function.

SHDN (Pin 8): Shutdown Pin. Pull this pin low for shut-

down mode. Tie to a voltage between 2V and 5.5V for

normal operation.

BLOCK DIAGRA

VIN 3

VC 1

FB 2

MODE 7

SHDN 8

RSENSE

0.08Ω

–

A1

V/I

+

0.62V

–+

A3

0.7V

ENABLE

SHUTDOWN

OSCILLATOR

SLOPE

A2

COMPENSATION

FLIP-FLOP

R

Q

S

SWITCH

DRIVER

RECTIFIER

DRIVE

BOOST DIODE

6 BOOST

SWITCH

5 SW

RECTIFIER

4 GND

1612 BD

sn1612 1612fs

5

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