LTM8080 datasheet(22/32 Pages) AD

22 / 32 page

LTM4703

Rev. 0

For more information www.analog.com

confusion and inconsistency. These definitions are given

in JESD51S-12, and are quoted or paraphrased below.

θJA is the natural convection junction-to-ambient

air thermal resistance measured in a 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

operating condition.

θJCbot is the junction-to-board thermal resistance with

all of the component power dissipation flowing through

the bottom of the package. In the typical μModule reg-

ulator, the bulk of the heat flows out the bottom of the

package, but there is always heat flow out into the ambi-

ent environment. As a result, this thermal resistance

value may be useful for comparing packages, but the

test conditions don’t generally match your application.

θJCtop is determined with nearly all of the compo-

nent power dissipation flowing through the top of the

package. As the electrical connections of the typical

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

θJCbot, this value may be useful

for comparing packages, but the test conditions don’t

generally match your application.

Given these definitions, it is clear that none of these

thermal coefficients reflect an actual physical operating

condition of the μModule regulator. Thus, none of them

can be individually used to accurately predict the thermal

performance of the product. Likewise, it would be inap-

propriate 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 the thermal resistances

simultaneously.

A graphical representation of these thermal resistances

is shown in Figure 8. Some thermal resistance elements,

such as heat flow out the side of the package, are not

defined by the JEDEC standard, and are not shown. The

blue resistances are contained within the µModule regu-

lator, and the green are outside.

The die temperature of the LTM4703 must be lower than

the maximum rating, so care must be taken in the layout

of the circuit to ensure good heat sinking of the LTM4703.

The bulk of the heat flow out of the LTM4703 is through

the bottom of the package and the pads into the printed

circuit board. Consequently, a poor printed circuit board

design can cause excessive heating, resulting in impaired

performance or reliability. See the PCB Layout section for

a printed circuit board design suggestion.

4703 F08

µModule DEVICE

θJCtop JUNCTION-TO-CASE

(TOP) RESISTANCE

θJA JUNCTION-TO-AMBIENT RESISTANCE

CASE (TOP)-TO-AMBIENT

RESISTANCE

BOARD-TO-AMBIENT

RESISTANCE

θJCbot JUNCTION-TO-CASE

(BOTTOM) RESISTANCE

JUNCTION

AMBIENT

CASE (BOTTOM)-TO-BOARD

RESISTANCE

Figure 8. Graphical Representation of Thermal Coefficients, Including JESD51-12 Terms

APPLICATIONS INFORMATION

LTM8080 Datasheet(PDF) 22 Page - Analog Devices

LTM8080 Datasheet(HTML) 22 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Download

Link URL