LTC3413 datasheet(6/16 Pages) LINER

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LTC3413

3413fc

Main Control Loop

The LTC3413 is a monolithic, constant frequency, current

mode step-down DC/DC converter that is capable of sourc-

ing and sinking current at the output. 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 on the VFB pin with a ref-

erence voltage that is equal to one-half of the voltage on

the VREF pin. When the load current increases, it causes

a reduction in the feedback voltage relative to the refer-

ence. 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 –7A.

The operating frequency is set by an external resistor

connected between the RT pin and ground. The switching

frequency can range from 300kHz to 2MHz.

Overvoltage and undervoltage comparators will pull the

PGOOD output low if the output voltage comes out of

regulation by ±10%. In an overvoltage condition, the top

power MOSFET is turned off and the bottom power MOSFET

is switched on until either the overvoltage condition clears

or the bottom MOSFET’s current limit is reached.

Dropout Operation

When the input supply voltage decreases toward the output

voltage, the duty cycle increases toward the maximum

on-time. Further reduction of the supply voltage forces the

–

PVIN

ITH

VREF

SVIN

SGND

VFB

PGOOD

SVIN

PVIN

SLOPE

COMPENSATION

RECOVERY

SLOPE

COMPENSATION

PMOS CURRENT

COMPARATOR

NMOS CURRENT

COMPARATOR

OSCILLATOR

ERROR

AMPLIFIER

LOGIC

RUN

RUN/SS

PGND

3413 BD

12 PGND

1.1VREF

0.9VREF

FUNCTIONAL DIAGRAM

OPERATION

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