PXS30 Datasheet, PDF (73/139 Pages) Freescale Semiconductor, Inc – PXS30 Microcontroller

Electrical characteristics
3.4 Thermal characteristics
Table 13. Thermal characteristics for package options¹
No. Symbol
Parameter
Conditions
Value
BGA BGA ^Unit
257 473
1 R_JA CC Thermal resistance junction-to-ambient Single layer board – 1s
natural convection²
 40  34 °C/W
2 R_JA CC Thermal resistance junction-to-ambient Four layer board – 2s2p
natural convection²
 22  20 °C/W
3 R_JMA CC Thermal resistance
junction-to-moving-air ambient²
@ 200 ft./min.,
single layer board – 1s
 32  26 °C/W
4 R_JMA CC Thermal resistance
junction-to-moving-air ambient²
@ 200 ft./min.,
four layer board – 2s2p
5 R_JB CC Thermal resistance junction-to-board³
—
6 R_JC CC Thermal resistance junction-to-case⁴
—
7 _JT CC Junction-to-package-top natural
—
convection⁵
 18  17 °C/W
 10  10 °C/W
 6  6 °C/W
 2  2 °C/W
NOTES:
1 _{Thermal characteristics are targets based on simulation that are subject to change per device characterization.}
2 _{Junction-to-Ambient thermal resistance determined per JEDEC JESD51-3 and JESD51-6. Thermal test board}
meets JEDEC specification for this package.
3 _{Junction-to-Board thermal resistance determined per JEDEC JESD51-8. Thermal test board meets JEDEC}
specification for the specified package.
4 _{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.
5 _{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.
3.4.1 General notes for specifications at maximum junction temperature
An estimation 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 (^oC)
R_JA = junction to ambient thermal resistance (^oC/W)
P_D = 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
PXS30 Microcontroller Data Sheet, Rev. 1
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
73