LTC1700_ 查看數據表（PDF） - Linear Technology

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LTC1700_

High Input Voltage, Current Mode Boost, Flyback and SEPIC Controller

Linear Technology 

LTC1871-7

PI FU CTIO S

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 cur-

rent 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 regulaton is 1.230V.

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

programs the operating frequency of the chip. The nomi-

nal 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

applied 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

capacitor. 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 connected 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 sens-

ing methods.

18717f

6

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