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LTM4649

4649fc

For more information www.linear.com/LTM4649

OPERATION

Power Module Description

The LTM4649 is a high performance single output stand-

alone nonisolated switching mode DC/DC power supply.

It can provide up to 10A output current with few exter-

nal input and output capacitors. This module provides

precisely regulated output voltage programmable via

an external resistor from 0.6VDC to 3.3VDC over a 4.5V

to 16V input range. The typical application schematic is

shown in Figure 17.

The LTM4649 has an integrated constant-frequency cur-

rent mode regulator, power MOSFETs, inductor, and other

supporting discrete components. The typical switching

frequency is 450kHz. For switching noise-sensitive ap-

plications, it can be externally synchronized from 400kHz

to 800kHz. See the Applications Information section.

With current mode control and internal feedback loop

compensation, the LTM4649 module has sufficient stabil-

ity margins and good transient performance with a wide

range of output capacitors, especially with all ceramic

output capacitors.

Current mode control provides cycle-by-cycle fast current

limit in an overcurrent condition. An internal overvoltage

monitor protects the output voltage in the event of an

overvoltage >10%. The top MOSFET is turned off and the

bottom MOSFET is turned on until the output is cleared.

Pulling the RUN pin below 1.1V forces the regulator into a

shutdown state. The TRACK/SS pin is used for program-

ming the output voltage ramp and voltage tracking during

start-up. See the Application Information section.

The LTM4649 is internally compensated to be stable over

all operating conditions. Table 3 provides a guideline for

input and output capacitances for several operating condi-

tions. LTpowerCAD™ is available for transient and stability

analysis. The VFBpinisusedtoprogramtheoutputvoltage

with a single external resistor to ground.

A remote sense amplifier is provided in the LTM4649 for

accuratelysensingoutputvoltages≤3.3Vattheloadpoint.

Multiphase operation can be easily employed with the

synchronization inputs using an external clock source.

See application examples.

High efficiency at light loads can be accomplished with

selectableBurstModeoperationusingtheMODEpin.These

light load features will accommodate battery operation.

Efficiency graphs are provided for light load operation in

the Typical Performance Characteristics section.

A TEMP pin is provided to allow the internal device tem-

peraturetobemonitoredusinganonboarddiodeconnected

PNP transistor. This diode connected PNP transistor is

grounded in the module and can be used as a general

temperature monitor using a device that is designed to

monitor the single-ended connection.

The switching node pin is available for functional opera-

tion monitoring. A resistor-capacitor snubber circuit can

be carefully placed from the switching node pin to ground

to dampen any high frequency ringing on the transition

edges.SeetheApplicationsInformationsectionfordetails.

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