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LTM4647

4647fb

For more information www.linear.com/LTM4647

OPERATION

Power Module Description

The LTM4647 is a high performance single output stand-

alone nonisolated switching mode DC/DC power supply.

It can provide a 30A output with few external input and

output capacitors. This module provides precisely regu-

lated output voltages programmable via external resistors

from 0.6V DC to 1.8V DC over a 4.7V to 15V input range.

The typical application schematic is shown in Figure 23

and Figure 24.

The LTM4647 has an integrated constant-frequency cur-

rent mode regulator, power MOSFETs, inductor,and other

supportingdiscretecomponents.Theswitchingfrequency

range is optimized from 400kHz to 700kHz, depending on

outputvoltage.Forswitchingnoise-sensitiveapplications,

it can externally program to or be synchronized to a clock

from 400kHz to 800kHz subject to minimum on-time and

inductor ripple current limitations. See the Applications

Information section.

The LTM4647 is designed to use either external or internal

controlloopcompensationbyshortingCOMPbandCOMPa

pins together. With current mode control, the internal

loop compensation has sufficient stability margins and

good transient performance with a wide range of output

capacitors, even with all ceramic output capacitors. Table

5 provides a guideline for input and output capacitances

for several different output conditions using the internal

loop compensation. The LTpowerCAD® design tool is

available to download for optimizing the loop stability and

transient response.

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 1.35V forces the regulator into

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

gramming the output voltage ramp and voltage tracking

during start-up. See the Application Information section.

Multiphase operation can be easily employed by cascad-

ing the MODE/PLLIN input to the CLKOUT output. See the

ApplicationsInformationsectionandFigure25forexample.

For high reliability environment, N+1 phase redundancy

can be easily implemented in LTM4647 together with a hot

swap controller, such as the LTC®4226, for extra system

protection. By connecting the HIZB pin to the gate of the

hot swap switch, any fault channel can be disconnected

while the rest of the system is not affected. See Applica-

tions Information section and Figure 27 for example.

High efficiency at light loads can be accomplished with

phase shedding in multiphase operation or with selectable

pulse-skipping mode or Burst Mode operation in single

phase operation. Efficiency graphs are provided for light

load operation in the Typical Performance Characteristics

section.

Aremotesenseamplifierisprovidedforaccuratelysensing

output voltages at the load point.

A TEMP+ and TEMP– pins are provided to allow the internal

device temperature to be monitored using an onboard

diode connected PNP transistor.

DECOUPLING REQUIREMENTS

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

CIN

External Input Capacitor Requirement

(VIN = 4.7V to 15V, VOUT = 1V)

IOUT = 30A

µF

COUT

External Output Capacitor Requirement

(VIN = 4.7V to 15V, VOUT = 1V)

IOUT = 30A

440

µF

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