LTC1872 datasheet(7/36 Pages) LINER

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LTC1871

1871fe

PIN FUNCTIONS

RUN (Pin 1): The RUN pin provides the user with an

accurate means for sensing the input voltage and pro-

gramming the start-up threshold for the converter. The

falling RUN pin threshold is nominally 1.248V and the

comparator has 100mV of hysteresis for noise immunity.

When the RUN pin is below this input threshold, the IC

is shut down and the VIN supply current is kept to a low

value (typ 10μA). The Absolute Maximum Rating for the

voltage on this pin is 7V.

ITH (Pin 2): Error Ampliﬁer Compensation Pin. The

current comparator input threshold increases with this

control voltage. Nominal voltage range for this pin is 0V

to 1.40V.

FB (Pin 3): Receives the feedback voltage from the external

resistor divider across the output. Nominal voltage for

this pin in regulation is 1.230V.

FREQ (Pin 4): A resistor from the FREQ pin to ground

programs the operating frequency of the chip. The nominal

voltage at the FREQ pin is 0.6V.

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 5.20V 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

capacitor.

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 the drain of the power MOSFET

for VDS sensing and highest efﬁciency. Alternatively, the

SENSE pin may be connected to a resistor in the source

of the power MOSFET. Internal leading edge blanking is

provided for both sensing methods.

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