LTM4622EY datasheet(16/28 Pages) LINER

16 / 28 page

LTM4622

Rev F

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APPLICATIONS INFORMATION

A graphical representation of the aforementioned ther-

mal resistances is given in Figure 7; blue resistances are

contained within the μModule regulator, whereas green

resistances are external to the µModule.

As a practical matter, it should be clear to the reader that

no individual or sub-group of the four thermal resistance

parameters defined by JESD 51-12 or provided in the

Pin Configuration section replicates or conveys normal

operating conditions of a μModule. For example, in nor-

mal board-mounted applications, never does 100% of

the device’s total power loss (heat) thermally conduct

exclusively through the top or exclusively through bottom

of the µModule—as the standard defines for θJCtop and

θJCbottom, respectively. In practice, power loss is ther-

mally dissipated in both directions away from the pack-

age—granted, in the absence of a heat sink and airflow,

a majority of the heat flow is into the board.

Within a SIP (system-in-package) module, be aware there

are multiple power devices and components dissipating

power, with a consequence that the thermal resistances

relative to different junctions of components or die are not

exactly linear with respect to total package power loss. To

reconcile this complication without sacrificing modeling

simplicity—but also, not ignoring practical realities—an

approach has been taken using FEA software modeling

along with laboratory testing in a controlled-environment

chamber to reasonably define and correlate the thermal

resistance values supplied in this data sheet: (1) Initially,

FEA software is used to accurately build the mechanical

geometry of the µModule and the specified PCB with all

of the correct material coefficients along with accurate

power loss source definitions; (2) this model simulates

a software-defined JEDEC environment consistent with

JSED51-12 to predict power loss heat flow and tempera-

ture readings at different interfaces that enable the cal-

culation of the JEDEC-defined thermal resistance values;

(3) the model and FEA software is used to evaluate the

µModule with heat sink and airflow; (4) having solved

for and analyzed these thermal resistance values and

simulated various operating conditions in the software

model, a thorough laboratory evaluation replicates the

simulated conditions with thermo-couples within a con-

trolled-environment chamber while operating the device

at the same power loss as that which was simulated. An

outcome of this process and due-diligence yields a set

of derating curves provided in other sections of this data

sheet. After these laboratory test have been performed

and correlated to the µModule model, then the θJB and

θBA are summed together to correlate quite well with the

µModule model with no airflow or heat sinking in a prop-

erly define chamber. This θJB + θBA value is shown in the

Pin Configuration section and should accurately equal

the θJA value because approximately 100% of power loss

Figure 8. 1V Output Power Loss

Figure 9. 1.5V Output Power Loss

Figure 10. 2.5V Output Power Loss

OUTPUT CURRENT (A)

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

4622 F08

12VIN

5VIN

OUTPUT CURRENT (A)

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

4622 F09

12VIN

5VIN

OUTPUT CURRENT (A)

2.5

2.0

1.5

1.0

0.5

4622 F10

12VIN

5VIN

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