MPC870 FREESCALE [Freescale Semiconductor, Inc], MPC870 Datasheet - Page 11

• Manufacturer Part Number: MPC870
• Description: Hardware Specifications
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Freescale Semiconductor
4
5
6
7 Thermal Calculation and Measurement
For the following discussions, P
drivers.
7.1 Estimation with Junction-to-Ambient Thermal Resistance
An estimation of the chip junction temperature, T
where:
The junction-to-ambient thermal resistance is an industry standard value that provides a quick and easy
estimation of thermal performance. However, the answer is only an estimate; test cases have demonstrated
that errors of a factor of two (in the quantity T
7.2 Estimation with Junction-to-Case Thermal Resistance
Historically, thermal resistance has frequently been expressed as the sum of a junction-to-case thermal
resistance and a case-to-ambient thermal resistance:
where:
R
affect the case-to-ambient thermal resistance, R
the device, add a heat sink, change the mounting arrangement on the printed circuit board, or change the
thermal dissipation on the printed circuit board surrounding the device. This thermal model is most useful
for ceramic packages with heat sinks where some 90% of the heat flows through the case and the heat sink
to the ambient environment. For most packages, a better model is required.
Input capacitance is periodically sampled.
A(0:31), TSIZ0/REG, TSIZ1, D(0:31), IRQ(2:4), IRQ6, RD/WR, BURST, IP_B(0:1), PA(0:4), PA(6:7), PA(10:11), PA15,
BDIP/GPL_B(5), BR, BG, FRZ/IRQ6, CS(0:7), WE(0:3), BS_A(0:3), GPL_A0/GPL_B0, OE/GPL_A1/GPL_B1,
θJC
PB19, PB(23:31), PC(6:7), PC(10:13), PC15, PD8, PE(14:31), MII1_CRS, MII_MDIO, MII1_TXEN, MII1_COL.
GPL_A(2:3)/GPL_B(2:3)/CS(2:3), UPWAITA/GPL_A4, UPWAITB/GPL_B4, GPL_A5, ALE_A, CE1_A, CE2_A,
OP(0:3) BADDR(28:30
is device-related and cannot be influenced by the user. The user adjusts the thermal environment to
T
T
R
P
R
R
R
R
A
D
J
θJA
θJA
θJA
θJC
θCA
= T
= ambient temperature ºC
= power dissipation in package
= junction-to-case thermal resistance (ºC/W)
= package junction-to-ambient thermal resistance (ºC/W)
= R
= junction-to-ambient thermal resistance (ºC/W)
= case-to-ambient thermal resistance (ºC/W)
A
The V
+ (R
θJC
θJA
+ R
DDSYN
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
× P
θCA
D
MPC875/MPC870 Hardware Specifications, Rev. 3.0
)
power dissipation is negligible.
D
= (V
DDL
×
I
J
DDL
–T
θCA
J
A
NOTE
, in °C can be obtained from the following equation:
) + P
) are possible.
. For instance, the user can change the airflow around
I/O
, where P
I/O
is the power dissipation of the I/O
Thermal Calculation and Measurement
11