MWCT1004AFVLLPR datasheet(59/65 Pages) NXP

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7.3 General notes for specifications at maximum junction

temperature

An estimation of the chip junction temperature, TJ, can be obtained from this equation:

where:

• TA = ambient temperature for the package (°C)

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

• PD = power dissipation in the package (W)

The junction to ambient thermal resistance is an industry standard value that provides a

quick and easy estimation of thermal performance. Unfortunately, there are two values in

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

board with two planes. For packages such as the PBGA, these values can be different by

a factor of two. Which value is closer to the application depends on the power dissipated

by other components on the board. 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:

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.

Thermal attributes

MWCT101XS Data Sheet, Rev. 3, 12/2019

NXP Semiconductors

MWCT1004AFVLLPR Datasheet(PDF) 59 Page - NXP Semiconductors