LTC3414MPFE datasheet(6/16 Pages) LINER

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LTC3414

3414fb

Main Control Loop

The LTC3414 is a monolithic, constant-frequency, cur-

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

operation, the internal top power switch (P-channel MOS-

FET) is turned on at the beginning of each clock cycle.

Current in the inductor increases until the current com-

parator 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 –5A for

forced continuous mode and 0A for Burst Mode operation.

The operating frequency is externally set by an external

resistor connected between the RT pin and ground. The

practical switching frequency can range from 300kHz to

4MHz.

Overvoltage and undervoltage comparators will pull the

PGOOD output low if the output voltage comes out of

regulation by

±7.5%. In an overvoltage condition, the top

power MOSFET is turned off and the bottom power MOS-

FET is switched on until either the overvoltage condition

clears or the bottom MOSFET’s current limit is reached.

Forced Continuous Mode

Connecting the SYNC/MODE pin to SVIN will disable Burst

Mode operation and force continuous current operation.

At light loads, forced continuous mode operation is less

efficient than Burst Mode operation, but may be desirable

in some applications where it is necessary to keep switch-

OPERATIO

BLOCK DIAGRA

–

SLOPE

COMPENSATION

RECOVERY

SLOPE

COMPENSATION

VOLTAGE

REFERENCE

OSCILLATOR

LOGIC

0.74V

0.86V

RUN

SVIN

SGND

EXPOSED PAD

ITH

PVIN

PMOS CURRENT

COMPARATOR

BCLAMP

VFB

RUN/SS

PGOOD

SYNC/MODE

PGND

CURRENT

REVERSAL

COMPARTOR

NMOS CURRENT

COMPARATOR

BURST

COMPARATOR

ERROR

AMPLIFIER

3414 BD

SYNC/MODE

0.8V

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