LTM4613 Просмотр технического описания (PDF) - Linear Technology
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LTM4613 Datasheet PDF : 30 Pages
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LTM4613
APPLICATIONS INFORMATION
application 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 of thermal performance.
Instead, the derating curves provided in the data sheet
can be used in a manner that yields insight and guidance
pertaining 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:
• θJA, the thermal resistance from junction to ambient, is
the natural convection junction-to-ambient air thermal
resistance measured in a one cubic foot sealed enclo-
sure. 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 95mm × 76mm PCB with 4 layers.
• θJCbottom, the thermal resistance from the junction
to the bottom of the product case, is determined
with all of the component power dissipation flowing
through the bottom of the package. In the typical
µModule regulator, the bulk of the heat flows out of
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
packages, but the test conditions do not generally
match the user’s application.
• θJCtop, the thermal resistance from the junction to the
top of the product case, is determined with nearly all of
the component power dissipation flowing through the
top of the package. As the electrical connections of the
µModule regulator are on the bottom of the package, 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 θJCbottom, this value may be useful
for comparing packages, but the test conditions do not
generally match the user’s application.
• θJB, the thermal resistance from the junction to the
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.
It is really the sum of the θJCbottom 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.
A graphical representation of the aforementioned thermal
resistances is given in Figure 8. Blue resistances are
contained within the µModule package, whereas green
resistances are external to the µModule package.
JUNCTION-TO-AMBIENT THERMAL RESISTANCE COMPONENTS
JUNCTION-TO-CASE (TOP)
RESISTANCE
CASE (TOP)-TO-AMBIENT
RESISTANCE
JUNCTION
JUNCTION-TO-BOARD RESISTANCE
JUNCTION-TO-CASE (BOTTOM) CASE (BOTTOM)-TO-BOARD
RESISTANCE
RESISTANCE
BOARD-TO-AMBIENT
RESISTANCE
AMBIENT
µModule REGULATOR
4613 F08
Figure 8. Graphical Representation of JESD51-12 Thermal Coefficients
For more information www.linear.com/LTM4613
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