LTM4613 datasheet(17/30 Pages) LINER

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LTM4613

4613fd

For more information www.linear.com/LTM4613

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,

notrelevanttoprovidingguidanceofthermalperformance.

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

tocorrelatethermalperformancetoone’sownapplication.

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.

Figure 8. Graphical Representation of JESD51-12 Thermal Coefficients

APPLICATIONS INFORMATION

µModule REGULATOR

4613 F08

JUNCTION

AMBIENT

JUNCTION-TO-CASE (TOP)

RESISTANCE

JUNCTION-TO-AMBIENT THERMAL RESISTANCE COMPONENTS

JUNCTION-TO-BOARD RESISTANCE

CASE (TOP)-TO-AMBIENT

RESISTANCE

BOARD-TO-AMBIENT

RESISTANCE

CASE (BOTTOM)-TO-BOARD

RESISTANCE

JUNCTION-TO-CASE (BOTTOM)

RESISTANCE

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