Datasheet

MPC8250 Hardware Specifications, Rev. 2
10 Freescale Semiconductor
Electrical and Thermal Characteristics
2.2 Thermal Characteristics
Table 4 describes thermal characteristics.
2.3 Power Considerations
The average chip-junction temperature, T
J
, in °C can be obtained from the following:
T
J
= T
A
+ (P
D
x
θ
JA
) (1)
where
T
A
= ambient temperature °C
θ
JA
= package thermal resistance, junction to ambient, °C/W
P
D
= P
INT
+ P
I/O
P
INT
= I
DD
x V
DD
Watts (chip internal power)
P
I/O
= power dissipation on input and output pins (determined by user)
For most applications P
I/O
< 0.3 x P
INT
. If P
I/O
is neglected, an approximate relationship between P
D
and
T
J
is the following:
P
D
= K/(T
J
+ 273° C) (2)
Solving equations (1) and (2) for K gives:
K = P
D
x (T
A
+ 273° C) +
θ
JA
x P
D
2
(3)
1
The default configuration of the CPM pins (PA[0–31], PB[4–31], PC[0–31], PD[4–31]) is input. To prevent excessive
DC current, it is recommended to either pull unused pins to GND or VDDH, or to configure them as outputs.
2
The leakage current is measured for nominal VDD, VCCSYN, and VDD.
Table 4. Thermal Characteristics
Characteristic Symbol
Value
Unit Air Flow
480 TBGA 516 PBGA
Junction to ambient—
single-layer board
1
1
Assumes no thermal vias
θ
JA
13 24
°C/W
Natural convection
10 18 1 m/s
Junction to ambient—
four-layer board
11 16 Natural convection
813 1 m/s
Junction to board
2
2
Thermal 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.
θ
JB
48°C/W —
Junction to case
3
3
Thermal resistance between the die and the case top surface as measured by the cold plate method (MIL SPEC-883
Method 1012.1).
θ
JC
1.1 6 °C/W —