LTM4644MPY datasheet(9/36 Pages) LINER

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LTM4644/LTM4644-1

4644fe

For more information www.linear.com/LTM4644

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

CIN

External Input Capacitor Requirement

(VIN = 4V to 14V, VOUT = 1.5V)

IOUT = 4A

4.7

µF

COUT

External Output Capacitor Requirement

(VIN = 4V to 14V, VOUT = 1.5V)

IOUT = 4A

µF

DECOUPLING REQUIREMENTS

OPERATION

The LTM4644 is a quad output standalone non-isolated

switch mode DC/DC power supply. It has four separate

regulator channels with each of them capable of delivering

up to 4A continuous output current with few external input

and output capacitors. Each regulator provides precisely

regulated output voltage programmable from 0.6V to 5.5V

viaasingleexternalresistor(tworesistorsforLTM4644-1)

over 4V to 14V input voltage range. With an external bias

voltage, this module can operate from an input voltage

as low as 2.375V. The typical application schematic is

shown in Figure 33.

TheLTM4644integratesfourseparateconstantfrequency

controlled on-time valley current mode regulators, power

MOSFETs, inductors, and other supporting discrete com-

ponents. The typical switching frequency is set to 1MHz.

For switching noise-sensitive applications, the µModule

regulator can be externally synchronized to a clock from

700kHz to 1.3MHz. See the Applications Information

section.

With current mode control and internal feedback loop

compensation, the LTM4644 module has sufficient stabil-

ity margins and good transient performance with a wide

range of output capacitors, even with all ceramic output

capacitors.

Current mode control provides the flexibility of paralleling

any of the separate regulator channels with accurate cur-

rent sharing. With a built-in clock interleaving between

each two regulator channels, the LTM4644 could easily

employ a 2+2, 3+1 or 4 channels parallel operation which

is more than flexible in a multirail POL application like

FPGA. Furthermore, the LTM4644 has CLKIN and CLK-

OUT pins for frequency synchronization or polyphasing

multiple devices which allow up to 8 phases cascaded to

run simultaneously.

Current mode control also provides cycle-by-cycle fast

current monitoring. Foldback current limiting is provided

in an overcurrent condition to reduce the inductor valley

current to approximately 40% of the original value when

VFB drops. An internal overvoltage and undervoltage

comparators pull the open-drain PGOOD output low if

the output feedback voltage exits a ±10% window around

the regulation point. Continuous conduction mode (CCM)

operation is forced during OV and UV conditions except

during start-up when the TRACK pin is ramping up to 0.6V.

Pulling the RUN pin below 1.1V forces the controller into

its shutdown state, turning off both power MOSFETs and

most of the internal control circuitry. At light load cur-

rents, discontinuous conduction mode (DCM) operation

can be enabled to achieve higher efficiency compared to

continuous conduction mode (CCM) by setting the MODE

pin to SGND. The TRACK/SS pin is used for power supply

trackingandsoft-startprogramming.SeetheApplications

Information section.

Atemperaturediodeisincludedinsidethemoduletomoni-

tor the temperature of the module. See the Applications

Information section for details.

(per Channel)

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