LTC1627 Просмотр технического описания (PDF) - Linear Technology

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LTC1627

Monolithic Synchronous Step-Down Switching Regulator

Linear Technology 

LTC1627

PIN FUNCTIONS

ITH (Pin 1): Error Amplifier Compensation Point. The

current comparator threshold increases with this control

voltage. Nominal voltage range for this pin is 0V to 1.2V.

RUN/SS (Pin 2): Combination of Soft-Start and Run

Control Inputs. A capacitor to ground at this pin sets the

ramp time to full current output. The time is approximately

0.5s/µF. Forcing this pin below 0.4V shuts down all the

circuitry.

VFB (Pin 3): Feedback Pin. Receives the feedback voltage

from an external resistive divider across the output.

GND (Pin 4): Ground Pin.

SW (Pin 5): Switch Node Connection to Inductor. This pin

connects to the drains of the internal main and synchro-

nous power MOSFET switches.

VIN (Pin 6): Main Supply Pin. Must be closely decoupled

to GND, Pin 4.

VDR (Pin 7): Top Driver Return Pin. This pin can be

bootstrapped to go below ground to improve efficiency at

low VIN (see Applications Information).

SYNC/FCB (Pin 8): Multifunction Pin. This pin performs

three functions: 1) secondary winding feedback input, 2)

external clock synchronization and 3) Burst Mode opera-

tion or forced continuous mode select. For secondary

winding applications connect a resistive divider from the

secondary output. To synchronize with an external clock

apply a TTL/CMOS compatible clock with a frequency

between 385kHz and 525kHz. To select Burst Mode opera-

tion, float the pin or tie it to VIN. Grounding Pin 8 forces

continuous operation (see Applications Information).

W

FUNCTIONAL DIAGRA

BURST

Y = “0” ONLY WHEN X IS A CONSTANT “1”

DEFEAT Y

VIN

X

1.5µA

VIN

VIN

SYNC/FCB

SLOPE

8

COMP

OSC

0.4V

0.6V –

VFB

3

+

VIN

0.8V

REF

UVLO

TRIP = 2.5V

SHUTDOWN

FREQ

SHIFT

0.8V

2.25µA

VIN

RUN/SS 2

+

EA

–

ITH 1

RUN/SOFT

START

0.86V

+

OVDET

–

–

0.8V

+ FCB

0.12V

– EN

+

BURST

SLEEP

–+

ICOMP

SQ

RQ

SWITCHING

LOGIC

AND

BLANKING

CIRCUIT

ANTI-

SHOOT-THRU

IRCMP

6 VIN

6Ω

7 VDR

5 SW

4 GND

1627 BD

5

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