LTC1627CS8 datasheet(5/16 Pages) LINER

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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).

FUNCTIONAL DIAGRA

VFB

VIN

0.12V

SWITCHING

LOGIC

AND

BLANKING

CIRCUIT

0.6V

ITH

RUN/SS

0.8V

0.4V

0.86V

SYNC/FCB

Y = “0” ONLY WHEN X IS A CONSTANT “1”

SHUTDOWN

SLEEP

Ω

1.5

µA

2.25

µA

VIN

VDR

GND

1627 BD

VIN

0.8V

BURST

OSC

FREQ

SHIFT

0.8V

REF

UVLO

TRIP = 2.5V

BURST

DEFEAT

SLOPE

COMP

–

OVDET

–

ICOMP

–

IRCMP

RUN/SOFT

START

FCB

ANTI-

SHOOT-THRU

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