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LTM4639

4639f

For more information www.linear.com/LTM4639

DECOUPLING REQUIREMENTS

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

CIN

External Input Capacitor Requirement

(VIN = 2.375V to 7V, VOUT = 1.5V),

CPWR ≥ 4.5V

IOUT = 20A, 4× 22µF Ceramic X7R Capacitors

(See Table 5)

µF

COUT

External Output Capacitor Requirement

(VIN = 2.375V to 7V, VOUT = 1.5V),

CPWR ≥ 4.5V

IOUT = 20A (See Table 5)

400

µF

TA = 25°C. Use Figure 1 configuration.

Power Module Description

The LTM4639 is a low input voltage,high performance

single output standalone nonisolated switching mode DC/

DC power supply. It can provide a 20A output with few

externalinputandoutputcapacitors.Thismoduleprovides

precisely regulated output voltages programmable via

external resistors from 0.6VDC to 5.5VDC over a 2.375V

to 7V input range. The typical application schematic is

shown in Figure 22.

TheLTM4639hasanintegratedconstant-frequencycurrent

mode regulator, power MOSFETs, 0.3µH inductor, and

other supporting discrete components. The switching

frequency range is from 250kHz to 770kHz, and the typical

operating frequency is shown in Table 5 for each VOUT. For

switching noise-sensitive applications, it can be externally

synchronizedfrom250kHzto800kHz,subjecttominimum

on-time limitations. A single resistor is used to program

the frequency. See the Applications Information section.

With current mode control and internal feedback loop

compensation, the LTM4639 module has sufficient

stability margins and good transient performance with

a wide range of output capacitors, even 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.

Overtemperature protection will turn off the regulator’s

RUNpinat~130°Cto137°C.SeeApplicationsInformation.

OPERATION

Pulling the RUN pin below 1.1V forces the regulator

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

programmingtheoutputvoltagerampandvoltagetracking

during start-up. See the Application Information section.

The LTM4639 is internally compensated to be stable over

all operating conditions with COMPA tied to COMPB. Table

5 provides a guideline for input and output capacitances

forseveraloperatingconditions.LTpowerCAD™isavailable

for transient and stability analysis. Custom compensation

can be used with the COMPA pin using the LTpowerCAD

and an external compensation network. The VFB pin is

used to program the output voltage with a single external

resistor to ground.

Aremotesenseamplifierisprovidedforaccuratelysensing

output voltages ≤3.3V at the load point.

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

selectable Burst Mode operation using the MODE_PLLIN

pin. These light load features will accommodate battery

operation. Efficiency graphs are provided for light load

operation in the Typical Performance Characteristics

section.

A TEMP+ and TEMP– pin is provided to allow the internal

device temperature to be monitored using an onboard

diode connected PNP transistor. This diode connected

PNP transistor can be used with TEMP monitor devices

like the LTC2990, LTC2997, LTC2974 and LTC2978.

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