LTM8026 LINER [Linear Technology], LTM8026 Datasheet - Page 21

• Manufacturer Part Number: LTM8026
• Description: 36VIN, 5A, 2-Quadrant CVCC Step-Down
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
θ
almost all of the heat flows through the bottom of the
µModule regulator and into the board, and is really the
sum of the θ
bottom of the part through the solder joints and through a
portion of the board. The board temperature is measured
a specified distance from the package, using a 2-sided,
2-layer board. This board is described in JESD 51-9.
Given these definitions, it should now be apparent that none
of these thermal coefficients reflects an actual physical
operating condition of a µModule regulator. 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 vs load graphs given
in the product’s data sheet. The only appropriate way to
use the coefficients is when running a detailed thermal
JB
is the junction-to-board thermal resistance where
JCbottom
JUNCTION
µMODULE DEVICE
and the thermal resistance of the
Figure 7. Thermal Resistances Among µModule Device,
(BOTTOM) RESISTANCE
JUNCTION-TO-CASE
JUNCTION-TO-AMBIENT RESISTANCE (JESD 51-9 DEFINED BOARD)
JUNCTION-TO-BOARD RESISTANCE
Printed Circuit Board and Environment
JUNCTION-TO-CASE (TOP)
RESISTANCE
CASE (BOTTOM)-TO-BOARD
RESISTANCE
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
device, and the green are outside.
The die temperature of the LTM8052 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
LTM8052. The bulk of the heat flow out of the LTM8052
is through the bottom of the module and the LGA pads
into the printed circuit board. Consequently a poor printed
circuit board design can cause excessive heating, result-
ing in impaired performance or reliability. Please refer to
the PCB Layout section for printed circuit board design
suggestions.
CASE (TOP)-TO-AMBIENT
BOARD-TO-AMBIENT
RESISTANCE
RESISTANCE
8052 F07
AMBIENT
LTM8052
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8052fa