LTM4650 datasheet(13/38 Pages) AD

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LTM4652

Rev. 0

For more information www.analog.com

OPERATION

Power Module Description

The LTM4652 is a bidirectional 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 or single ±50A

output with few external input and output capacitors and

setup components. This module provides precisely regu-

lated output voltages programmable via external resistors

from 0.6VDC to 7.5VDC over 4.5V to 18V input voltages.

The typical application schematic is shown in Figure 31.

The LTM4652 has dual integrated constant-frequency

current mode regulators and built-in power MOSFET

devices with fast switching speed. The typical switching

frequency is 300kHz* to 780kHz depending on different

input and output conditions. For switching-noise sensi-

tive applications, it can be externally synchronized from

300kHz* to 780kHz. A resistor can be used to program a

free run frequency on the fSET pin. See the Applications

Information section.

With current mode control, multiple LTM4652s can be

easily paralleled to provide up to ±300A current with

excellent current sharing. Also, with current mode control,

the LTM4652 module is able to achieve sufficient stability

margins and a very fast ±3% output transient response

with a minimum number of output capacitors, even with

all ceramic output capacitors. This makes LTM4652 the

best candidate when powering FPGAs, ASICs and pro-

cessors in terms of DC accuracy, AC transient response,

high output current and accuracy current sharing. See

Applications Information section.

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 reg-

ulation 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 protection is feedback voltage referred.

If desired, latch-off input overvoltage protection can

be implemented by connecting an appropriate resistor,

*Note that synchronization below 400kHz is not tested in ATE.

RVINOVP, from VIN to VINOVP. When the VINOVP pin

exceeds 1.22V, switching action ceases, i.e., both the top

MOSFET and bottom MOSFET are latched off. The module

can be restarted by cycling the RUN pins below their RUN

thresholds, or by cycling the TRACK pins to SGND or by

cycling VIN altogether.

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

used for soft-starting the regulator. See the Applications

Information section.

The LTM4652 has a built-in 10pF high frequency filter

cap from COMP to SGND for each channel. An exter-

nal RC filtering circuit is required to achieve fast Type II

control loop compensation. Table 6 provides a guide line

for input, output capacitances and R-C values on COMP

pin for several operating conditions. The Analog Devices

µModule Power Design Tool (LTpowerCAD®) provides for

transient and stability analysis. The VFB pin is used to pro-

gram 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.

High efficiency at light loads can be accomplished with

selectable pulse-skipping operation using the MODE_

PLLIN pin. This light load feature will accommodate bat-

tery operation. Efficiency graphs are provided for light load

operation in the Typical Performance Characteristics sec-

tion. See the Applications Information section for details.

A general purpose diode-configured PNP temperature

sensor is included inside the module to monitor the tem-

perature of the module. See the Applications Information

section for details.

The switch pins, SW1 and SW2, are available for func-

tional operation monitoring and a resistor-capacitor

snubber circuit can be careful 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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