Analog Devices LTM4683 Manual page 68

LTM4683
APPLICATIONS INFORMATION
performed on a µModule package mounted to a hardware
test board defined by JESD51-9 ("Test Boards for Area
Array Surface Mount Package Thermal Measurements").
The motivation for providing these thermal coefficients is
found in JESD51-12 ("Guidelines for Reporting and Using
Electronic Package Thermal Information").
Many designers may opt to use laboratory equipment
and a test vehicle, such as the demo board, to predict the
µModule regulator's thermal performance in their appli-
cation at various electrical and environmental operating
conditions to compliment any FEA activities. Without
FEA software, the thermal resistances reported in the Pin
Configuration section are in-and-of themselves not relevant
to providing guidance on thermal performance; instead,
the derating curves provided later in this data sheet can
be used in a manner that yields insight and guidance per-
taining to one's application-usage, and can be adapted to
correlate thermal performance to one's own application.
The Pin Configuration section gives four thermal coeffi-
cients explicitly defined in JESD51-12; these coefficients
are quoted or paraphrased below.
1. θ , the thermal resistance from the junction to ambi-
JA
ent, is the natural convection junction-to-ambient air
thermal resistance measured in one cubic foot sealed
enclosure. This environment is sometimes referred to
as "still air", although natural convection causes the
air to move. This value is determined with the part
mounted to a JESD51-9 defined test board, which
does not reflect an actual application or viable operat-
ing condition.
JUNCTION
µModule DEVICE
68
JUNCTION-TO-AMBIENT THERMAL RESISTANCE COMPONENTS
JUNCTION-TO-CASE (TOP)
RESISTANCE
JUNCTION-TO-BOARD RESISTANCE
JUNCTION-TO-CASE CASE (BOTTOM)-TO-BOARD
(BOTTOM) RESISTANCE
Figure 34. Graphical Representation of JESD51-12 Thermal Coefficients
For more information
2. θ , the thermal resistance from the junction to
JCbottom
the bottom of the product case, is determined with all
of the component power dissipation flowing through
the bottom of the package. In a typical µModule regu-
lator, the bulk of the heat flows out the bottom of
the package, but there is always heat flow out into
the ambient environment. As a result, this thermal
resistance value may be useful for comparing pack-
ages, but the test conditions don't generally match
the user's application.
3. θ
, the thermal resistance from the junction to the
JCtop
top of the product case, is determined with nearly all
component power dissipation flowing through the top
of the package. As the electrical connections of a typi-
cal µModule regulator are on the bottom of the pack-
age, it is rare for an application to operate such that
most of the heat flows from the junction to the top of
the part. As in the case of θ
useful for comparing packages, but the test conditions
don't generally match the user's application.
4. θ
, the thermal resistance from the junction to the
JB
printed circuit board, 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 the sum of the θ
mal resistance of the bottom of the part through the
solder joints and through a portion of the board. The
board temperature is measured at a specified distance
from the package, using a two-sided, two-layer board.
This board is described in JESD51-9.
CASE (TOP)-TO-AMBIENT
RESISTANCE
BOARD-TO-AMBIENT
RESISTANCE RESISTANCE
www.analog.com
, this value may be
JCbottom
and the ther-
JCbottom
AMBIENT
4683 F33
Rev. 0