參數(shù)資料
型號: MPC8248CZQP
廠商: Motorola, Inc.
英文描述: MPC8272 PowerQUICC II Family Hardware Specifications
中文描述: MPC8272的PowerQUICC II系列硬件規(guī)格
文件頁數(shù): 13/56頁
文件大?。?/td> 539K
代理商: MPC8248CZQP
MOTOROLA
MPC8272 PowerQUICC II Family Hardware Specifications
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
For More Information On This Product,
Go to: www.freescale.com
13
Thermal Characteristics
4.5
Experimental Determination
To determine the junction temperature of the device in the application after prototypes are available, the
thermal characterization parameter (
Ψ
JT
) can be used to determine the junction temperature with a
measurement of the temperature at the top center of the package case using the following equation:
T
J
= T
T
+ (
Ψ
JT
×
P
D
)
where:
Ψ
JT
= thermal characterization parameter
T
T
= thermocouple temperature on top of package
P
D
= power dissipation in package
The thermal characterization parameter is measured per JEDEC JESD51-2 specification using a 40 gauge
type T thermocouple epoxied to the top center of the package case. The thermocouple should be positioned
so that the thermocouple junction rests on the package. A small amount of epoxy is placed over the
thermocouple junction and over 1 mm of wire extending from the junction. The thermocouple wire is placed
flat against the case to avoid measurement errors caused by cooling effects of the thermocouple wire.
4.6
Layout Practices
Each V
CC
pin should be provided with a low-impedance path to the board’s power supply. Each ground pin
should likewise be provided with a low-impedance path to ground. The power supply pins drive distinct
groups of logic on chip. The V
CC
power supply should be bypassed to ground using at least four 0.1 μF
bypass capacitors located as close as possible to the four sides of the package. The capacitor leads and
associated printed circuit traces connecting to chip V
CC
and ground should be kept to less than half an inch
per capacitor lead. A four-layer board employing two inner layers as V
CC
and GND planes is recommended.
All output pins on the MPC8272 have fast rise and fall times. Printed circuit (PC) trace interconnection
length should be minimized in order to minimize overdamped conditions and reflections caused by these
fast output switching times. This recommendation particularly applies to the address and data buses.
Maximum PC trace lengths of six inches are recommended. Capacitance calculations should consider all
device loads as well as parasitic capacitances due to the PC traces. Attention to proper PCB layout and
bypassing becomes especially critical in systems with higher capacitive loads because these loads create
higher transient currents in the V
CC
and GND circuits. Pull up all unused inputs or signals that will be inputs
during reset. Special care should be taken to minimize the noise levels on the PLL supply pins.
4.7
References
Semiconductor Equipment and Materials International
805 East Middlefield Rd.
Mountain View, CA 94043
MIL-SPEC and EIA/JESD (JEDEC) Specifications
(Available from Global Engineering Documents)
JEDEC Specifications
1. C.E. Triplett and B. Joiner, “An Experimental Characterization of a 272 PBGA Within an
Automotive Engine Controller Module,” Proceedings of SemiTherm, San Diego, 1998, pp. 47
54.
2. B. Joiner and V. Adams, “Measurement and Simulation of Junction to Board Thermal Resistance
and Its Application in Thermal Modeling,” Proceedings of SemiTherm, San Diego, 1999, pp.
212
220.
(415) 964-5111
800-854-7179 or
303-397-7956
http://www.jedec.org
F
Freescale Semiconductor, Inc.
n
.
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