Motorola MCF5281, MCF5282 user manual Thermal Characteristics, 2lists thermal resistance values

Thermal Characteristics

33.2 Thermal Characteristics

Table 33-2lists thermal resistance values.

Table 33-2. Thermal Characteristics

Characteristic		Symbol	Value	Unit
Junction to ambient, natural convection	Four layer board (2s2p)	θJMA	261,2	°C/W
Junction to ambient (@200 ft/min)	Four layer board (2s2p)	θJMA	231,2	°C/W
Junction to board		θJB	153	°C/W
Junction to case		θJC	104	°C/W
Junction to top of package	Natural convection	Ψjt	21,5	°C/W

1θJMA and Ψjt parameters are simulated in accordance with EIA/JESD Standard 51-2 for natural convection. Motorola recommends the use of θJA and power dissipation specifications in the system design to prevent device junction temperatures from exceeding the rated specification. System designers should be aware that device junction temperatures can be significantly influenced by board layout and surrounding devices. Conformance to the device junction temperature specification can be verified by physical measurement in the customer’s system using the Ψjt parameter, the device power dissipation, and the method described in EIA/JESD Standard 51-2.

2Per JEDEC JESD51-6 with the board horizontal.

3Thermal resistance between the die and the printed circuit board per JEDEC JESD51-8. Board temperature is measured on the top surface of the board near the package.

4Thermal resistance between the die and the case top surface as measured by the cold plate method (MIL SPEC-883 Method 1012.1).

5Thermal characterization parameter indicating the temperature difference between 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.

The average chip-junction temperature (TJ) in °C can be obtained from:

TJ = TA + (PD ⋅ ΘJMA)(1)

Where:

TA= Ambient Temperature, ×C

QJMA= Package Thermal Resistance, Junction-to-Ambient, ×C/W

PD= PINT + PI/O

PINT= IDD ¥ VDD, Watts - Chip Internal Power

PI/O= Power Dissipation on Input and Output Pins — User Determined

For most applications PI/O < PINT and can be neglected. An approximate relationship between PD and TJ (if PI/O is neglected) is:

MOTOROLA Chapter 33. Electrical Characteristics 33-3