Datasheet

LTM8055/LTM8055-1
18
Rev C
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APPLICATIONS INFORMATION
Given these definitions, it should now be apparent that none
of these thermal coefficients reflects an actual physical
operating condition of a µModule converter. Thus, none
of them can be individually used to accurately predict the
thermal performance of the product. Likewise, it would
be inappropriate to attempt to use any one coefficient to
correlate to the junction temperature versus load graphs
given in the product’s data sheet. The only appropriate way
to use the coefficients is when running a detailed thermal
analysis, such as FEA, which considers all of the thermal
resistances simultaneously.
A graphical representation of these thermal resistances
is given in Figure 7.
The blue resistances are contained within the µModule
converter, and the green are outside.
The die temperature of the LTM8055/LTM8055-1 must be
lower than the maximum rating of 125°C, so care should
be taken in the layout of the circuit to ensure good heat
sinking of the LTM8055/LTM8055-1. The bulk of the heat
flow out of the LTM8055/LTM8055-1 is through the bottom
of the μModule converter and the BGA pads into the printed
circuit board. Consequently a poor printed circuit board
design can cause excessive heating
, resulting
in impaired
performance or reliability. Please refer to the PCB Layout
section for printed circuit board design suggestions.
Figure 7
8055 F07
µMODULE CONVERTER
JUNCTION-TO-CASE (TOP)
RESISTANCE
JUNCTION-TO-BOARD RESISTANCE
JUNCTION-TO-AMBIENT RESISTANCE (JESD 51-9 DEFINED BOARD)
CASE (TOP)-TO-AMBIENT
RESISTANCE
BOARD-TO-AMBIENT
RESISTANCE
JUNCTION-TO-CASE
(BOTTOM) RESISTANCE
JUNCTION AMBIENT
CASE (BOTTOM)-TO-BOARD
RESISTANCE
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