MPXD2005VMM80R datasheet(76/119 Pages) FREESCALE

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PXS20 Microcontroller Data Sheet, Rev. 1

Preliminary—Subject to Change Without Notice

Electrical characteristics

Freescale Semiconductor

3.4.1

General notes for specifications at maximum junction temperature

An estimation of the chip junction temperature, TJ, can be obtained from Equation 1:

TJ =TA +(RJA ×PD)

Eqn. 1

where:

= ambient temperature for the package (oC)

RJA

= junction to ambient thermal resistance (oC/W)

= 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 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)

Table 11. Thermal characteristics for 257 MAPBGA package1

1 Thermal characteristics are targets based on simulation that are subject to change per device characterization.

Symbol

Parameter

Conditions

Value Unit

RJA

Thermal resistance junction-to-ambient natural

convection2

2 Junction-to-Ambient thermal resistance determined per JEDEC JESD51-3 and JESD51-6. Thermal test board

meets JEDEC specification for this package.

Single layer board – 1s

°C/W

Four layer board – 2s2p

RJMA

Thermal resistance, junction-to-ambient forced

convection at 200 ft/min

Single layer board – 1s

°C/W

Four layer board – 2s2p

RJB

Thermal resistance junction-to-board3

3 Junction-to-Board thermal resistance determined per JEDEC JESD51-8. Thermal test board meets JEDEC

specification for the specified package.

—13

°C/W

RJC

Thermal resistance junction-to-case4

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.

—8

°C/W



Junction-to-package-top natural convection5

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.

—2

°C/W

MPXD2005VMM80R Datasheet(PDF) 76 Page - Freescale Semiconductor, Inc

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