LTC3412 datasheet(7/22 Pages) AD

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LTC3412

3412fc

For more information www.linear.com/LTC3412

FUNCTIONAL BLOCK DIAGRAM

–

0.74V

ERROR

AMPLIFIER

SYNC/MODE

BURST

COMPARATOR

BCLAMP

NMOS

CURRENT

COMPARATOR

PMOS CURRENT

COMPARATOR

REVERSE

CURRENT

COMPARATOR

0.86V

RUN

RUN/SS

P-CH

N-CH

PGOOD

ITH

VFB

0.8V

SYNC/MODE

3412 FBD

PVIN

SGND

SVIN

SLOPE

COMPENSATION

VOLTAGE

REFERENCE

OSCILLATOR

LOGIC

SLOPE

COMPENSATION

RECOVERY

–

PGND

+–

OPERATION

Main Control Loop

The LTC3412 is a monolithic, constant-frequency, current

mode step-down DC/DC converter. During normal opera-

tion, the internal top power switch (P-channel MOSFET) is

turned on at the beginning of each clock cycle. Current in

the inductor increases until the current comparator trips

and turns off the top power MOSFET. The peak inductor

current at which the current comparator shuts off the top

power switch is controlled by the voltage on the ITH pin.

The error amplifier adjusts the voltage on the ITH pin by

comparing the feedback signal from a resistor divider on

the VFB pin with an internal 0.8V reference. When the load

current increases, it causes a reduction in the feedback

voltage relative to the reference. The error amplifier raises

the ITH voltage until the average inductor current matches

the new load current. When the top power MOSFET shuts

off, the synchronous power switch (N-channel MOSFET)

turns on until either the bottom current limit is reached or

the beginning of the next clock cycle. The bottom current

limit is set at –2A for forced continuous mode and 0A for

Burst Mode operation.

The operating frequency is set by an external resistor

connected between the RT pin and ground. The practical

switching frequency can range from 300kHz to 4MHz.

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