Datasheet

where:
R
ΘJA
= junction-to-ambient thermal resistance (°C/W)
R
ΘJC
= junction-to-case thermal resistance (°C/W)
R
ΘCA
= case to ambient thermal resistance (°C/W)
R
ΘJC
is device related and is not affected by other factors. The thermal environment can
be controlled to change the case-to-ambient thermal resistance, R
ΘCA
. For example,
change the air flow around the device, add a heat sink, change the mounting arrangement
on the printed circuit board, or change the thermal dissipation on the printed circuit board
surrounding the device. This description is most useful for packages with heat sinks
where 90% of the heat flow is through the case to heat sink to ambient. For most
packages, a better model is required.
A more accurate two-resistor thermal model can be constructed from the junction-to-
board thermal resistance and the junction-to-case thermal resistance. The junction-to-case
thermal resistance describes when using a heat sink or where a substantial amount of heat
is dissipated from the top of the package. The junction-to-board thermal resistance
describes the thermal performance when most of the heat is conducted to the printed
circuit board. This model can be used to generate simple estimations and for
computational fluid dynamics (CFD) thermal models. More accurate compact Flotherm
models can be generated upon request.
To determine the junction temperature of the device in the application on a prototype
board, use the thermal characterization parameter (Ψ
JT
) to determine the junction
temperature by measuring the temperature at the top center of the package case using the
following equation:
where:
T
T
= thermocouple temperature on top of the package (°C)
Ψ
JT
= thermal characterization parameter (°C/W)
P
D
= power dissipation in the package (W)
The thermal characterization parameter is measured in compliance with the JESD51-2
specification using a 40-gauge type T thermocouple epoxied to the top center of the
package case. Position the thermocouple so that the thermocouple junction rests on the
package. Place a small amount of epoxy on the thermocouple junction and approximately
Package information
MPC5777C Microcontroller Data Sheet Data Sheet, Rev. 13, 08/2018.
86 NXP Semiconductors