P9242-R datasheet(24/31 Pages) IDT

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P9242-R Datasheet

December 16, 2016

11. Application Information

11.1 Power Dissipation and Thermal Requirements

The P9242-R is offered in a 48-VFQFN package that has a maximum power dissipation capability of about 1.47W. The maximum power

dissipation of the package is determined by the number of thermal vias between the package and the printed circuit board (PCB). The

maximum power dissipation of the package is defined by the die’s specified maximum operating junction temperature, TJ(MAX) of 125°C. The

junction temperature rises when the heat generated by the device’s power dissipation flow is impeded by the package-to-PCB thermal

resistance.

The VFQFN package offers a typical thermal resistance, junction to ambient (θJA), of 27.2°C/W when the PCB layout design is optimized as

described in the P9242-R Layout Guide document. The techniques noted in the PCB layout section must be followed when designing the

printed circuit board layout. Attention to the placement of the P9242-R and bridge FET packages in proximity to other heat-generating devices

in a given application design should also be considered. The ambient temperature around the power IC will also have an effect on the thermal

limits of an application. The main factors influencing θJA (in the order of decreasing influence) are PCB characteristics, die/package attached

thermal pad size (VFQFN) and thermal vias, and the final system hardware construction. Board designers should keep in mind that the

package thermal metric θJA is impacted by the characteristics of the PCB. Changing the design or configuration of the PCB changes the

overall thermal resistivity and the board’s heat-sinking efficiency.

Three basic approaches for enhancing thermal performance are listed below:



Improving the power dissipation capability of the PCB design.



Improving the thermal coupling of the component to the PCB.



Introducing airflow into the system.

First, the maximum power dissipation for a given situation should be calculated using Equation 2:

PD(MAX) =

(TJ(MAX) − TA)

θJA

Equation 2

Where

PD(MAX) = Maximum power dissipation

θJA = Package thermal resistance (°C/W)

TJ(MAX) = Maximum device junction temperature (°C)

TA = Ambient temperature (°C)

The maximum recommended operating junction temperature (TJ(MAX)) for the P9242-R is 125°C. The thermal resistance of the 48-pin VFQFN

package (NDG48) is optimally θJA=27.2°C/W. Operation is specified to a maximum steady-state ambient temperature (TA) of 85°C. Therefore,

the maximum recommended power dissipation is given by the following equation:

PD(Max) = (125°C - 85°C) / 27.2°C/W ≅ 1.47 Watt

All the previously mentioned thermal resistances are the values found when the P9242-R is mounted on a standard board of the dimensions

and characteristics specified by the JEDEC 51 standard.

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