LTG4 datasheet(7/32 Pages) LINER

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LTC1871-7

18717fc

PIN FUNCTIONS

MODE/SYNC (Pin 5): This input controls the operating

mode of the converter and allows for synchronizing the

operating frequency to an external clock. If the MODE/

SYNC pin is connected to ground, Burst Mode operation

is enabled. If the MODE/SYNC pin is connected to INTVCC,

or if an external logic-level synchronization signal is ap-

plied to this input, Burst Mode operation is disabled and

the IC operates in a continuous mode.

GND (Pin 6): Ground Pin.

GATE (Pin 7): Gate Driver Output.

INTVCC (Pin 8): The Internal 7V Regulator Output. The

gate driver and control circuits are powered from this

voltage. Decouple this pin locally to the IC ground with

a minimum of 4.7μF low ESR tantalum or ceramic ca-

pacitor. This 7V regulator has an undervoltage lockout

circuit with 5.6V and 4.6V rising and falling thresholds,

respectively.

VIN (Pin 9): Main Supply Pin. Must be closely decoupled

to ground.

SENSE (Pin 10): The Current Sense Input for the Control

Loop. Connect this pin to a resistor in the source of the

power MOSFET. Alternatively, the SENSE pin may be con-

nected to the drain of the power MOSFET, in applications

where the maximum VDS is less than 36V. Internal leading

edge blanking is provided for both sensing methods.

BLOCK DIAGRAM

1.230V

85mV

50k

START-UP

CONTROL

BURST

COMPARATOR

LOGIC

PWM LATCH

CURRENT

COMPARATOR

0.30V

1.230V

5.6V UP

4.6V DOWN

1.230V

SLOPE

1.230V

ILOOP

ITH

MODE/SYNC

FREQ

INTVCC

LDO

V-TO-I

OSC

V-TO-I

SLOPE

COMPENSATION

BIAS AND

START-UP

CONTROL

VIN

BIAS

VREF

IOSC

RLOOP

–

SENSE

GND

18717 BD

GATE

INTVCC

GND

VIN

1.248V

RUN

0.6V

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