PXS30 Datasheet, PDF (74/139 Pages) Freescale Semiconductor, Inc – PXS30 Microcontroller

Electrical characteristics
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 Equation 2 as the sum of a junction to case
thermal resistance and a case to ambient thermal resistance:
R_JA = R_JC + R_CA
Eqn. 2
where:
R_JA = junction to ambient thermal resistance (°C/W)
R_JC = junction to case thermal resistance (°C/W)
R_CA = case to ambient thermal resistance (°C/W)
R_JC is device related and cannot be influenced by the user. The user controls the thermal environment to
change the case to ambient thermal resistance, R_CA. 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 (_JT) can be used to determine the junction temperature with a
measurement of the temperature at the top center of the package case using Equation 3:
T_J = T_T + (_JT × P_D)
Eqn. 3
where:
T_T = thermocouple temperature on top of the package (°C)
_JT = thermal characterization parameter (°C/W)
P_D = 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 package. A small amount of epoxy is placed over the
thermocouple junction and over about 1 mm of wire extending from the junction. The thermocouple wire
is placed flat against the package case to avoid measurement errors caused by cooling effects of the
thermocouple wire.
See [6] to [10] in Section 6, Reference documents, for more information.
3.5 Electromagnetic interference (EMI) characteristics
3.5.1 Test Setup
Electromagnetic emission tests are performed by TEM cell [2] and via direct coupling [3] (150 Ohm)
measurements.
Electromagnetic immunity are measured by DPI [4].
PXS30 Microcontroller Data Sheet, Rev. 1
74
Preliminary—Subject to Change Without Notice
Freescale Semiconductor