LTM8062EVPBF datasheet(16/20 Pages) LINER

16 / 20 page

LTM8062

8062f

APPLICATIONS INFORMATION

to add an electrolytic bulk capacitor to the VIN net. This

capacitor’s relatively high equivalent series resistance

damps the circuit and eliminates the voltage overshoot.

The extra capacitor improves low frequency ripple filter-

ing and can slightly improve the efficiency of the circuit,

though it is physically large.

Thermal Considerations

The thermal performance of the LTM8062 is given in the

Typical Performance Characteristics section. These curves

were generated by the LTM8062 mounted to a 58cm2

4-layer FR4 printed circuit board. Boards of other sizes

and layer count can exhibit different thermal behavior, so

it is incumbent upon the user to verify proper operation

over the intended system’s line, load and environmental

operating conditions.

For increased accuracy and fidelity to the actual application,

many designers use FEA to predict thermal performance.

To that end, the Pin Configuration section of the data sheet

typically gives four thermal coefficients:

θJA: Thermal resistance from junction to ambient.

θJCbottom: Thermal resistance from junction to the bot-

tom of the product case.

θJCtop: Thermal resistance from junction to top of the

product case.

θJB: Thermal resistance from junction to the printed

circuit board.

While the meaning of each of these coefficients may seem

to be intuitive, JEDEC has defined each to avoid confusion

and inconsistency. These definitions are given in JESD

51-12, 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 JESD 51-9 defined test board, which does not reflect

an actual application or viable operating condition.

θJCbottom 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, 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 re-

sistance value may be useful for comparing packages

but the test conditions don’t generally match the user’s

application.

θJCtop is determined with nearly all of the component

power dissipation flowing through the top of the pack-

age. As the electrical connections of the typical μModule

are on the bottom of the package, it is rare for an ap-

plication to operate such that most of the heat flows

from the junction to the top of the part. As in the case

θJCbottom, this value may be useful for comparing

packages but the test conditions don’t generally match

the user’s application.

θJB is the junction-to-board thermal resistance where

almost all of the heat flows through the bottom of the

μModule and into the board, and is really the sum of the

θJCbottomandthethermalresistanceofthebottomofthe

part through the solder joints and through a portion of

the board. The board temperature is measured a speci-

fied distance from the package, using a two sided, two

layer board. This board is described in JESD 51-9.

The most appropriate way to use the coefficients is when

running a detailed thermal analysis, such as FEA, which

considers all of the thermal resistances simultaneously.

None of them can be individually used to accurately pre-

dict the thermal performance of the product, so it would

be inappropriate to attempt to use any one coefficient to

correlate to the junction temperature versus load graphs

given in the LTM8033 data sheet.

A graphical representation of these thermal resistances

is given in Figure 8.

The blue resistances are contained within the μModule,

and the green are outside.

The die temperature of the LTM8062 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

LTM8062. The bulk of the heat flow out of the LTM8062

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, result-

ing in impaired performance or reliability. Please refer to

the PCB Layout section for printed circuit board design

suggestions.

LTM8062EVPBF Datasheet(PDF) 16 Page - Linear Technology

LTM8062EVPBF Datasheet(HTML) 16 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL