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LTM4650-2

Rev. 0

For more information www.analog.com

OPERATION

POWER MODULE DESCRIPTION

The LTM4650-2 is a dual-output standalone nonisolated

switching mode DC/DC power supply with ±1.5% total DC

output error over line, load and temperature variation. It

can provide two 25A outputs with few external input and

output capacitors and setup components. This module

provides precisely regulated output voltages program-

mable via external resistors from 0.6VDC to 1.8VDC over

4.5V to 15V input voltages. The typical application sche-

matic is shown in Figure 24.

The LTM4650-2 has dual integrated constant-frequency

current mode regulators and built-in power MOSFET

devices with fast switching speed. The typical switching

frequency is from 400kHz to 600kHz, depending on the

output voltage. For switching-noise sensitive applications,

it can be externally synchronized from 400kHz to 750kHz.

A resistor can be used to program a free run frequency

on the fSET pin. See the Applications Information section.

With current mode control, the LTM4650-2 module has

sufficient stability margins and good transient perfor-

mance with a wide range of output capacitors, even with

all ceramic output capacitors.

Current mode control provides cycle-by-cycle fast current

limit and foldback current limit in an overcurrent condi-

tion. Internal overvoltage and undervoltage comparators

pull the open-drain PGOOD outputs low if the output

feedback voltage exits a ±10% window around the regu-

lation point. As the output voltage exceeds 10% above

regulation, the bottom MOSFET will turn on to clamp the

output voltage. The top MOSFET will be turned off. This

overvoltage protect is feedback voltage referred.

Pulling the RUN pins below 1.1V forces the regulators

into a shutdown state by turning off both MOSFETs. The

TRACK pins are used for programming the output voltage

ramp and voltage tracking during start-up or for soft-

starting the regulator. See the Applications Information

section.

An external RC filtering circuit is required to achieve fast

Type II control loop compensation. Table 4 provides a

guideline for input, output capacitances and RC COMP

values for several operating conditions. The Analog

Devices µModule power design tool (LTpowerCAD) will be

provided for transient and stability analysis. The VFB pin is

used to program the output voltage with a single external

resistor to ground. A differential remote sense amplifier

is available for sensing the output voltage accurately on

one of the outputs at the load point or in parallel operation

sensing the output voltage at the load point.

The multiphase operation can be easily employed with

the MODE_PLLIN, PHASMD, and CLKOUT pins. Up to

12 phases can be cascaded to run simultaneously with

respect to each other by programming the PHASMD pin to

different levels. See the Applications Information section.

High efficiency at light loads can be accomplished with

selectable Burst Mode operation or pulse-skipping

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. See the Applications

Information section for details.

A general-purpose temperature diode is included inside

the module to monitor the temperature of the module. See

the Applications Information section for details.

The switch pins are available for functional operation

monitoring, and a resistor-capacitor snubber circuit can

be carefully placed on the switch pin to ground to dampen

any high-frequency ringing on the transition edges. See

the Applications Information section for details.

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