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LTM4634

4634f

For more information www.linear.com/LTM4634

operaTion

Power Module Description

The LTM4634 µModule regulator is a high performance

triple output nonisolated switching mode DC/DC power

supply. It can provide 5A/5A/4A outputs with a few ex-

ternal input and output capacitors. This module provides

precisely regulated output voltages programmable via

external resistors from 0.8V DC to 5.5V DC (VOUT1 and

VOUT2), and 0.8V DC to 13.5V DC (VOUT3). When apply-

ing control bias in the range from 4.75V to 5.8V, then

connect the bias to CNTL_PWR and INTVCC, otherwise

if >5.8V only the CNTL_PWR pin needs to be biased. The

typical application schematic is shown in Figure 22.

TheLTM4634hasthreeintegratedconstant-frequencycur-

rent mode regulators, power MOSFETs, power inductors,

and other supporting discrete components. The typical

switching frequency is 750kHz. For switching noise-

sensitive applications, it can be externally synchronized

from 250kHz to 750kHz. Operating frequency range will

be dependent upon specific VIN and VOUT requirements

as they pertain to minimum on-time and inductor ripple

current of less than 60% of the load current. See the Ap-

plications Information section.

With current mode control and internal feedback loop

compensation, the LTM4634 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 cycle-by-cycle fast current

limit in an overcurrent condition. An internal overvoltage

monitor protects the output voltages in the event of an

overvoltage >10%. The top MOSFET is turned off and the

bottom MOSFET is turned on until the output overvoltage

is cleared. There are two temperatures monitors in the

LTM4634. TEMP1 monitors the close relative tempera-

ture of channels 1 and 2, and TEMP2 monitors the close

relative temperature of channels 2 and 3. The two diode

connected PNP transistors are grounded in the module

and can be used as general purpose temperature monitors

usingadevicethatisdesignedtomonitorthesingle-ended

connection.

Pulling any of the RUN pins below 1.15V forces that

regulator channel into a shutdown state. The TK/SS pins

are used for programming the output voltage ramp and

voltage tracking during start-up for each of the channels.

See the Applications Information section.

TheLTM4634isinternallycompensatedtobestableoverall

operatingconditions.Table4providesaguidelineforinput

and output capacitances for several operating conditions.

The LTpowerCAD™ software tool is provided for transient

and stability analysis. The VFB pin is used to program the

output voltage with a single external resistor to ground.

Each of the channels, operate 120° phase shift for mul-

tiphase operation. VOUT1 and VOUT2 can be combined to

provide a single 10A output. The two channels will not be

operating180°phaseshift,but120°phasewhencombined

for a 10A design. So the input RMS current may be higher

than a 180° phase shifted design. See the Applications

Information section for details.

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 op-

erationintheTypicalPerformanceCharacteristicssection.

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