FS32R274VBK2MMM datasheet(71/78 Pages) NXP

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The junction to ambient thermal resistance is an industry standard parameter that

provides a quick and easy estimation of thermal performance. However, junction to board

thermal resistance is more appropriate for tight enclosure spaces where board temperature

should be used as reference temperature. Using 2s2p board with natural convection

conditions, junction temperature is found to be less than 150°C . There are two

parameters in common usage: the value determined on a single layer board and the value

obtained on a board with two inner planes. For packages such as PBGA, these values can

significantly differ. For customer board design with different number of layers and

copper percentage content, these values must be appropriately interpolated in order to

evaluate junction temperature. In general, the value obtained on a single layer board is

appropriate for the tightly packed printed circuit board. The value obtained on the board

with the internal planes is usually appropriate if the board has low power dissipation and

the components are well separated.

When a heat sink is used, the thermal resistance is expressed in the following equation as

the sum of a junction-to-case thermal resistance and a case-to-ambient thermal resistance:

RθJA = RθJC + RθCA

where:

• RθJA = junction to ambient thermal resistance (°C/W)

• RθJC = junction to case thermal resistance (°C/W)

• RθCA = case to ambient thermal resistance (°C/W)

RθJC is device related and cannot be influenced by the user. The user controls the thermal

environment to change the case to ambient thermal resistance, RθCA. For instance, the

user can change the size of the heat sink, the air flow around the device, the interface

material, the mounting arrangement on printed circuit board, or change the thermal

dissipation on the printed circuit board surrounding the device.

To determine the junction temperature of the device in the application when heat sinks

are not used, the Thermal Characterization Parameter (

ΨJT) can be used to determine the

junction temperature with a measurement of the temperature at the top center of the

package case using this equation:

TJ = TT + (ΨJT × PD)

where:

• TT = thermocouple temperature on top of the package (°C)

•

ΨJT = thermal characterization parameter (°C/W)

• PD = power dissipation in the package (W)

The thermal characterization parameter is measured per JESD51-2 specification using a

40 gauge type T thermocouple epoxied to the top center of the package case. The

thermocouple should be positioned so that the thermocouple junction rests on the

Thermal Specifications

S32R274/S32R264 Series Data Sheet, Rev. 6, 06/2021

NXP Semiconductors

FS32R274VBK2MMM Datasheet(PDF) 71 Page - NXP Semiconductors

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