P9242-R3/RB Datasheet

© 2019 Integrated Device Technology, Inc.

35

May 17, 2019

12. Application Information

12.1 Power Dissipation and Thermal Requirements

The P9242-R3 is offered in a 48-VFQFPN 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 VFQFPN 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-R3 Layout Guide document. The techniques noted in the PCB layout section must be followed when designing the

printed circuit board layout. Take into consideration possible proximity to other heat-generating devices when placing the P9242-R3 and the

bridge FET packages in a given application design. 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 (VFQFPN), 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)−TAMB�

θJA

Equation 2

Where:

PD(MAX) = Maximum power dissipation

θJA = Package thermal resistance (°C/W)

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

TAMB = Ambient temperature (°C)

The maximum recommended operating junction temperature (TJ(MAX)) for the P9242-R3 is 125°C. The thermal resistance of the 48-pin VFQFPN

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

the maximum recommended power dissipation is given by Equation 3:

PD(MAX) =

(125°C−85°C)

27.2°C/W

≅1.47Watt

Equation 3

All the above-mentioned thermal resistances were determined with the P9242-R3 mounted on a standard board of the dimensions and

characteristics specified by the JEDEC 51 standard.