LTC3413

6

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

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

a reduction in the feedback voltage relative to the refer-

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

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

–

+

–

+

16

10

9

3

6

1

8

SGND

4

PGOOD

SLOPE

COMPENSATION

RECOVERY

SLOPE

COMPENSATION

PMOS CURRENT

COMPARATOR

NMOS CURRENT

COMPARATOR

OSCILLATOR

ERROR

AMPLIFIER

LOGIC

RUN

RUN/SS

11

14

15

SW

SW

SW

SW

13

7

5

PGND

3413 BD

12 PGND

2

2

2

FUNCTIONAL DIAGRAM

OPERATION