LTM4631 datasheet(22/34 Pages) LINER

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LTM4631

4631fb

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simulated various operating conditions in the software

model, a thorough laboratory evaluation replicates the

simulated conditions with thermocouples within a con-

trolled-environment chamber while operating the device

at the same power loss 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 correlate quite well with the

µModule model with no airflow or heat sinking in a prop-

erly 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 LTM4631 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.

Figures 10 and 11 show temperature plots of the LTM4631

doing a paralleled 12V to 1.0V at 20A design with no air-

flow and 12V to 1.8V at 20A design with 200LFM airflow.

applicaTions inForMaTion

Safety Considerations

The LTM4631 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 needs

to be provided to protect each unit from catastrophic fail-

ure. The device does support over current protection. A

temperature diode is provided for monitoring internal

temperature, and can be used to detect the need for ther-

mal shutdown that can be done by controlling the RUN

pin.

Power Derating

The 1.0V and 1.5V power loss curves in Figures 13 and 14

can be used in coordination with the load current derating

curves in Figures 15 to 22 for calculating an approximate

ΘJA thermal resistance for the LTM4631 with various heat

sinking and airflow conditions. The power loss curves are

taken at room temperature, and are increased with a 1.20

multiplicative factor at 125°C.

The derating curves are plotted with CH1 and CH2 in

parallel single output operation starting at 20A of load

with low ambient temperature. The output voltages are

1.0V and 1.5V. These are chosen to include the lower

and higher output voltage ranges for correlating the ther-

mal resistance. Thermal models are derived from several

temperature measurements in a controlled temperature

chamber along with thermal modeling analysis.

Figure 10. Thermal Image 12V to 1.0V,

20A with No Air Flow and No Heat Sink

Figure 11. Thermal Image 12V to 1.8V,

20A with 200LFM and No Heat Sink

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