PXD10 Datasheet, PDF (63/130 Pages) Lumins Inc. – 4” Dia.X 6” extruded aluminum step poles

Electrical characteristics
3 _{Junction-to-case at the top of the package determined using MIL-STD 883 Method 1012.1. The cold plate}
temperature is used for the case temperature. Reported value includes the thermal resistance of the interface layer.
4 _{Thermal characterization parameter indicating the temperature difference between the package top and the}
junction temperature per JEDEC JESD51-2. When Greek letters are not available, the thermal characterization
parameter is written as Psi-JT.
3.5.1 General notes for specifications at maximum junction temperature
An estimate of the chip junction temperature, T_J, can be obtained from Equation 1:
T_J = T_A + (R_JA  P_D)
Eqn. 1
where:
T_A = ambient temperature for the package (°C)
R_JA = junction to ambient thermal resistance (°C/W)
P_D = power dissipation in the package (W)
The thermal resistance values used are based on the JEDEC JESD51 series of standards to provide
consistent values for estimations and comparisons. The difference between the values determined for the
single-layer (1s) board compared to a four-layer board that has two signal layers, a power and a ground
plane (2s2p), demonstrate that the effective thermal resistance is not a constant. The thermal resistance
depends on the:
• Construction of the application board (number of planes)
• Effective size of the board which cools the component
• Quality of the thermal and electrical connections to the planes
• Power dissipated by adjacent components
Connect all the ground and power balls to the respective planes with one via per ball. Using fewer vias to
connect the package to the planes reduces the thermal performance. Thinner planes also reduce the thermal
performance. When the clearance between the vias leave the planes virtually disconnected, the thermal
performance is also greatly reduced.
As a general rule, the value obtained on a single-layer board is within the normal range for the tightly
packed printed circuit board. The value obtained on a board with the internal planes is usually within the
normal range if the application board has:
• One oz. (35 micron nominal thickness) internal planes
• Components are well separated
• Overall power dissipation on the board is less than 0.02 W/cm²
The thermal performance of any component depends on the power dissipation of the surrounding
components. In addition, the ambient temperature varies widely within the application. For many natural
convection and especially closed box applications, the board temperature at the perimeter (edge) of the
package is approximately the same as the local air temperature near the device. Specifying the local
ambient conditions explicitly as the board temperature provides a more precise description of the local
ambient conditions that determine the temperature of the device.
PXD10 Microcontroller Data Sheet, Rev. 1
Freescale Semiconductor
63