LTM4630A datasheet(21/38 Pages) LINER

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LTM4630A

4630afb

For more information www.linear.com/LTM4630A

operating conditions in the software model, a thorough

laboratory evaluation replicates the simulated conditions

with thermocouples within a controlled-environment

chamberwhileoperatingthedeviceatthesamepowerloss

as that which was simulated. An outcome of this process

and due-diligence yields a set of derating curves provided

in other sections of this data sheet. After these laboratory

test have been performed and correlated to the µModule

model, then the θJB and θBA are summed together to cor-

relate quite well with the µModule model with no airflow or

heat sinking in a properly define chamber. This θJB + θBA

value is shown in the Pin Configuration section and should

accurately equal the θJA value because approximately

100% of power loss flows from the junction through the

board into ambient with no airflow or top mounted heat

sink. Each system has its own thermal characteristics,

therefore thermal analysis must be performed by the user

in a particular system.

The LTM4630A module has been designed to effectively

remove heat from both the top and bottom of the pack-

age. The bottom substrate material has very low thermal

resistance to the printed circuit board. An external heat

sink can be applied to the top of the device for excellent

heat sinking with airflow.

Figures10and11showtemperatureplotsoftheLTM4630A

with no heat sink and 200LFM airflow.

These plots equate to a paralleled 12V to 1.0V at 36A

design operating at 86.5% efficiency, and 12V to 3.3V at

36A design operating at 93.7% efficiency.

APPLICATIONS INFORMATION

Safety Considerations

The LTM4630A modules do not provide isolation from

VIN to VOUT. There is no internal fuse. If required, a slow

blow fuse with a rating twice the maximum input current

needstobeprovidedtoprotecteachunitfromcatastrophic

failure. The device does support over current protection.

A temperature diode is provided for monitoring internal

temperature,andcanbeusedtodetecttheneedforthermal

shutdown that can be done by controlling the RUN pin.

Power Derating

The 1.0V, 1.8V, 3.3V, 5V and 8V power loss curves in

Figures 13 to 17 can be used in coordination with the load

current derating curves in Figures 18 to 33 for calculating

an approximate ΘJA thermal resistance for the LTM4630A

with various heat sinking and airflow conditions. The

power loss curves are taken at room temperature, and are

increased with a 1.35 to 1.4 multiplicative factor at 125°C.

These factors come from the fact that the power loss of the

regulator increases about 45% from 25°C to 150°C, thus a

50% spread over 125°C delta equates to ~0.35%/°C loss

increase. A 125°C maximum junction minus 25°C room

temperature equates to a 100°C increase. This 100°C

increase multiplied by 0.35%/°C equals a 35% power loss

increase at the 125°C junction, thus the 1.35 multiplier.

The derating curves are plotted with CH1 and CH2 in

parallel single output operation starting at 36A of load

with low ambient temperature. The output voltages are

1.0V, 1.8V, 3.3V, 5V and 8V. These are chosen to include

the lower and higher output voltage ranges for correlating

the thermal resistance. Thermal models are derived from

several temperature measurements in a controlled tem-

perature chamber along with thermal modeling analysis.

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