Datasheet
LTM8052/LTM8052A
22
8052fc
For more information www.linear.com/LTM8052
Figure 7. Thermal Resistances Among µModule Device,
Printed Circuit Board and Environment
8052 F07
µMODULE DEVICE
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
θ
JB
is the junction-to-board thermal resistance where
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
JCbottom
and the thermal resistance of the
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
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/LTM8052A 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/LTM8052A. The bulk of the
heat flow out of the LTM8052/LTM8052A 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, resulting in impaired
performance or reliability. Please refer to the PCB Layout
section for printed circuit board design suggestions.
applicaTions inForMaTion